Anotherpower.com Forum
Renewable Energy Questions/Discussion => Automation, Controls, Inverters, MPPT, etc => Topic started by: Burnit0017 on January 08, 2012, 07:16:57 am
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Greetings, I am new to the forum. I recently constructed and tested a working PMA and VAWT. At 40 MPH it will produce 9 amps DC using a 12 volt deep cell for a test load.
I started a project for a very basic buck converter to determine if it will produce a higher output from my PMA at a lower wind speed.
As I understand the circuit charges the output inductor when the MOSFET is on.
When the MOSFET is off, the turbine will be allowed to maintain a higher RPM and the energy stored in the inductor will discharge current into the battery.
The output voltage will always be fixed to the battery voltage.
The input voltage will change as the turbine RPM changes.
The input voltage will be high with low current and the output voltage will be low with higher current because the energy stored in the large output inductor will discharge into the battery as the MOSFET turns on and off.
I have all the parts to fabricate a very basic low amp output buck converter.
I am trying to design the basic test circuit so a micro controller can be added if required.
This is a first attempt at designing a power circuit. I have a basic understanding of all the concepts involved and comments are welcome.
Mod Edit: Removed the You-Tube Clip as it promotes that Snake Oil guy
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Hi, I started fabrication of the output part of the circuit. There will be three separate circuit boards:
1. diode and output inductor
2. MOSFET and input capacitor
3. timing circuit
I have used the timing circuit on other project so I know it will work.
I am using this article as a guide to determine component valves.
Power Electronics Technology_ June 2006 “Buck-Converter Design Demystified”
http://my.ece.ucsb.edu/Bobsclass/194/References/NonIsolated/Buck/Buck%20Converter%20Design%20Demystified%20606PET25.pdf
I have to determine what switching frequency will work best for this application?
Comments welcome.
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Nice post, I think I will be watching that guys progress and yours.
This now gives me ideas for a project.
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http://www.aliexpress.com/product-fm/488055373-150W-500W-wind-controller-12v-24v-switched-auto-wholesalers.html
Hi, commercially availably MPPT.
-->Mod EDIT.
Generally we will wish for a certain number of posts before allowing links to outside sites.
This is to discourage, and control spammers and search engine loaders.
However there has not been a consensus among the mods and admins of what this number should be.
As such we have not posted that in any rules as of yet (early days).
All that aside, this IS the kind of link that IS RELEVANT, and fitting to the topic.
This link also does not appear its meant for any alternative agenda such as boosting a site ranking
A posting like this as per moderators discretion MAY be over looked for these reasons even if that
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Thank you for the good example Burnit0017
<--
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Hi, I am making progress. I purchased more binding posts so I can more easily change the cap and inductor with different values. I am working on the gate oscillator. The biggest challenge is finding away to connect the boards that will able to carry the increased current. The first test circuit will have a five amp maximum limit mainly because the only diodes I could find have a 3 amp rating. I am running two in parallel. What I find curious is the inductor I fabricated from the equation provided in the article would not fit in their case. I have no association with commercial item.
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Hi, project update.
Waiting for ordered parts.
I found a link that shows sensor to measure current if micro control is required.
http://scienceshareware.com/how-to-measure-AC-DC-current-with-a-hall-effect-clamp-.htm
I do not know if the switch frequency has to be adjustable for the circuit to function at different wind speeds.
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The switch frequency has no bearing on the function.... just the design difficulty.
Use a set frequency, and change your pulse width (duty cycle) to achieve whatever control parameters you are going to use via your controller.
For a first time go, I have these simple rules I have garnered from blowing up lots of fets.
Keep the frequency low (20khz).
Make a current limiting circuit part of your design
Drive the fets with a low impedance driver (transformer or dedicated driver or high current driver )
Separate the grounds so interference from the power stage does not leak into the signal stage
Dont saturate the core........ and....
Do it in the basement so no-one can hear the Fets scream before they toddle off into the afterlife.
A lot has been said to NOT breadboard these pwm things. It is mostly true, and a lot of design work is done to get the layout perfect.... to protect against stray leakage etc.
At lower frequencies, this is also true, but you can still do a whole lot of interesting things at the birdsnest stage, and get results to move on with. It is surprising what will actually work in a mess..... until you turn the current up that little bit more..... then it can be problematic.
Try hard to turn the fets fully on fast and fully off fast...... with a very square wave. This is where the dreaded heat can be bought down to an acceptable level from a otherwise cooking fet.
I would experiment with analogue devices first until you get the feel of control and how things work.... then you can confuse the issues further with programming, as by then you will know how varying the parameters actually change the workings of the switcher.
My experiences with PWM tells me an oscilloscope is virtually mandatory. Without it, your at a loss to fault find and correct poor performance when it is attached to wave form, and switching times, leakage, damping, peak switching voltages, spikes etc etc.
I found PWM switching is a minefield of things waiting to destroy your fets, but when you beat the problems one by one it is rewarding.
Just my take on it anyhow. Hope it helps
................oztules
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Hi, I received a recommendation to add a voltage comparator that would turn off the MOSFET when the input voltage is lower than the battery voltage. This will be the first circuit to determine what else will needed for buck converter. I should be able measure input current and compare it the output current. Because the controller circuit will be on a bread board it will be easy to make improvements after I have a working buck converter.
Thank you for the information. I ordered the O scope. If I can get this first test running than I can make improvements.
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Hi, the new used oscilloscope arrived. It displays the calibration wave form on each channel. What connections are needed to view the AC output of the PMA?
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Hi, the new used oscilloscope arrived. It displays the calibration wave form on each channel. What connections are needed to view the AC output of the PMA?
Ahh, posting on both.... thats fine, I'd far rather respond here anyway. We don't have so many argumentative ignoramuses :)
I've got a similar scope - couple of models up I think, the Tek 2445.
(http://tools.rossw.net/tek-2445a.jpg)
If you connect ONLY ONE CHANNEL with the input of that channel set to DC (not AC, reason later), and clip your input lead across any one coil (that's any two phase wires if they're in delta, or any phase and the star point in star/wye), you should see one phase (one of the three).
DO NOT CONNECT MORE THAN ONE CHANNEL AT THIS TIME, because you will find that all channels "ground" is the same. Putting more than one channel on, will very likely let out magic smoke. ALSO, CHECK FIRST that your 'scope ground doesn't have any potential to your generator output - star point or whichever phase you wish to use for the earth. If it does, you will need an isolating transformer for the scope.
In the absence of a suitable transformer, you MAY get away with using a suitable voltage, AC-rated capacitor in series with the ground lead of your scopes input. Around 2.2uF 630V would be a good place to start.
Edit: I forgot. The reason for DC not AC is that your input signal could be fairly low frequency, and the AC coupled input on the scope will affect how it displays your signal. It may not display it at all, whereas the DC coupling will show you exactly what's going on, including any DC offset.
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Hi, thank you for the help. Spinning the PMA by hand I am to confirm that the PMA does produce a sine wave output.
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Hi, I spent the last few days trying to get the nand gate oscillator to oscillate and show the output wave form on the O-scope. Step one complete, next is the voltage multiplier. I will post updates when available.
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Hi, 10 volts in, 20 volts out. Voltage multiplier is working. It is time to add a mosfet and the control circuit for input A.
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Nice waveform..... look at it long and hard...... coz thats the shape you want to see on the gate/s when the current starts to get going. Not always easy.
..............oztules
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Hi, The RC timing constant at the voltage multiplier output is not allowing a pulsed output. The output of the voltage multiplier has 1.5 volt ripple riding at 20 volts and is not discharging to zero, so the MOSFET will never turn off when point A is enabled. I am searching for alternatives. Ordering a gate driver is the obvious solution. Comments welcome.
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Oh dear, thats a fet cooking waveform you have there.
You will be well advised to use a dedicated PWM chip...... from any computer power supply, and start with something that will actually work.
Use the op amps in the chip for your multiplying (change the feedback gain) and switch off - function/current limiting, and the chip will do the house keeping better than discrete circuitry. You can also use the deadtime control for remote operation / micro control/ override/control.... or any combination of the above. They are very accommodating in this way.
Totem pole transistors will give you pretty good low impedance fet switching, but a dedicated driver will be even simpler, with even less problems to worry about.
I really don't think this circuit is worth the perseverance.... sorry :(
...............oztules
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Hi, there is nothing to be sorry for. The circuit worked for a small DC motor driver, but it is clearly not going to work as a MOSFET gate driver, so it time to move on and find a suitable MOSFET and gate driver IC. Thank you for the help I have been receiving. I will post updates when available. At some point it will work. Thanks again.
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The slopes are killing the fets.
A ghurd controller can have an output like this (but he is not able to entertain more thoughts about MPPT at this time),
G-
(http://i701.photobucket.com/albums/ww20/ghurd1/Ghurd%20Controller%20O-Scope/dump_current_hi_duty_cycle_640.jpg)
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The slopes are killing the fets.
A ghurd controller can have an output like this (but he is not able to entertain more thoughts about MPPT at this time),
G-
(http://i701.photobucket.com/albums/ww20/ghurd1/Ghurd%20Controller%20O-Scope/dump_current_hi_duty_cycle_640.jpg)
You say "5 amps per division" on the vertical axis.... you're obviously not referring to gate drive here then? (In which case it'd be 5 volts per division? And if it were 5V/div, that'd be close to 13V gate drive even at the low end of the slope - which should have been quite enough to saturate drain/source??)
So are you saying that the slope on the leading edge of the "high" part of the cycle - current starts high, then decays a bit, then holds steady? What do you attribute that to?
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Hi, a TC4420CPA has been recommended for the gate drive. I am just trying to get a basic buck converter to work at this time. It has been a number of years since I have thought about any circuit operation and all problems will find a solution.
Because I am using cmos nand gates and a 12 volt deep cell for Vdd, the output of just the nand oscillator may be enough to drive the mosfet gate. The data sheet for the IRF510 says Vgs at 10 volts has a continuous current at I drain of about 5 amps but I am not sure if I am reading the information correctly. I should know more soon, thank you for all the help I have been receiving.
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It's not just the voltage, it's the switch current.
If you must use cmos 4000 series chips, at least use a hex schmitt trigger, all paralleled, and you may achieve the drive necessary.
...............oztules
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I'm using an MC34151 dual driver chip because they are cheap and a stock item at the local emporium!! Works well driving four off IRF1405 75amp MOSFETS in my dump load controller.
You can check out the circuit and layout at http://gilks.ath.cx/~g8ecj/New_Turbine/new_controller.html (http://gilks.ath.cx/~g8ecj/New_Turbine/new_controller.html) which ensures low stray currents, proper decoupling of the driver chip, opto isolator drive and gate protection using high speed schottky diodes and damping resistors.
Not sure how fast it will run but my 50MHz scope can only just see the edges when switching at just under 1KHz
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Nice project Frackers.....
I've never ended up using opto isolators to actively drive the driver circuits before... i found switching time was laggy... but i didn't try 1khz either I guess....
If you get the wave you say, then maybe i didn't persevere enough with them.... although I try to keep above 20khz, and they didn't seem keen to keep up with a clean wave.
.............oztules
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Hi, is it possible to have a transistor configuration to oscillate Vgs?
When point “A” is enabled the voltage at point X will be 2 times the battery voltage.
MOSFET source is always at the plus value of the battery voltage and is consider ground with respect to Vgs.
The MOSFET requires 10 volts at the gate to turn on.
Use a resistive voltage divider to create a high and low side of the voltage at point X.
Configure a transistor circuit on the high side of the voltage divider to provide 10 volts to gate.
I do not have a lot of experience with transistor circuits, comments are welcome.
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Hi, update of basic buck converter circuit.
When voltage at point C is greater than the battery voltage
point A is enabled
point X is 24 volts
The top nand gate oscillator and inverter toggle the transistor switches
turning the MOSFET on and off.
I am ordering gate driver IC’s.
I will post test results when available. Comments welcome.
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You must reference the Vgs voltage to the source.... not ground.
..............oztules
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Hi, I am having a lot of confusion trying to determine what voltage is required to turn on the MOSFET.
I am using a IRF510. The data sheet info says Vgs is +- 20 volts and the gate(thershold) is 2 to 4 volts.
If the source is connected to +12 volts, what voltage value is needed at the gate to turn on the MOSFET?
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Try to drive it with a square wave. 0v for off and +13v saturated on.. this voltage is for the gate REFERENCED to the source.... nothing else matters to it, only the voltage between the source and the gate.
If you look at how a field effect device works you will see why this is.
Long story short. We have a NPN structure. We'll call the first N doped silicon the source, the P doped one next to it (is isolated for this story), and then the last N doped silicon is our drain.
If we put our source to ground, and our drain to a positive... the electrons can go from the left N into the doped P but get stopped at the next P-N barrier (reversed biased diode really).
So nothing happens.
Now we place an insulated layer on top of the NPN silicon matrix... then a conductor that sits on that.... thats the gate. It is not connected to anything else at this stage.... so still nothing happens.
Now if we place a potential between the insulated gate +, and the source, we create an electric field. This effects the P layer (pushes the positive carriers away, creating a N inversion layer), and basically turns it into a N substrate.... now we have a NNN from source to drain, acting as a single block of N type material... the more positive .....the more conductive the new "N" layer so the resistance is all gone... it's turned on.
If we now take away the gate charge and drive it back to the same potential as the source... it turns back into a reversed biased diode... and the channel no longer conducts.
Do you now see why you MUST reference the gate to the source. You cant generate the electric field above the matrix and turn the P into N unless it is with respect to the source.... nor can you turn it off again unless you bring it back to source potential.
Note the gate is insulated from the other substrate, which gives us a very high impedance input.
Beyond +-20v Vgs, will puncture the isolation to the gate, 3 volts is enough electric field to start turning the N channel on, and conduction begins. We need to turn it up to 12-15v to for enough electric field to make darn sure it is fully on.
You do not want a partially turned on source drain path. You want it off or on..... nothing in between.
At least thats how I remember it. There are probably a few more things to worry about (body diode, capacitance etc), But thats the gusts of it I think.
Someone else can correct any blues.
................oztules
Edit spelling
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I re labeled the voltage divider.
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Hi, waveform verifying function of nand oscillator and npn transistors switching circuit.
circuit update: all the parts of the control circuit are working, switching frequency @ 4 k.
Next I will try to piece them together and try to trigger the MOSFET.
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I re labeled the voltage divider.
I might be missing something here - but if that's an N-channel FET, and you have the drain to the supply, how do you ever plan to turn it on?
Somehow, you need to get the gate about 10V higher than the source - and without some extra supply, I just don't see how you can do it. When the FET is off, the source will be (close to) ground, and sure - you can easily make Vgs more than enough to turn it on... but as it starts to turn on, resistance Drain-Source lowers, and V(source) aproaches V(drain), so whatever you have on the gate is going to be not enough to keep the FET saturated, it'll turn itself off (or more correctly, stop turning itself on). It's a lot like an emitter resistor in a conventional BJT.
Or, am I missing something in your circuit??
Edit: Actually, it's even worse than I thought. In my mind, I saw the battery as a "load", not a 12V supply.
So the Source is never going to go "lower" than +12V, and your CMOS chip is driving the FET GATE - yet the CMOS is powered from the battery, so you can NEVER get the gate higher than the source, much less 10V higher.
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Exactly.... and the only way he can drive the gate 12v or more positive than the source will be with an isolated gate driver of some type. Simplest is the small torroid transformer coupling. Any other method that looks at ground and not just the gate source relationship, will get feedback from the changing value of the battery and the freewheel diode.
I was beginning to think it was just me.... but I'm not getting through... even explaining how the field effect was used for conduction... so all I can do is leave it to you and quote this from my last post
"Do you now see why you MUST reference the gate to the source. You cant generate the electric field above the matrix and turn the P into N unless it is with respect to the source.... nor can you turn it off again unless you bring it back to source potential."
It's that simple.
Pulls pin from grenade... holds between teeth... and slowly counts down :P
.................oztules
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Hi Burnit,
Mosfets,mosfets,mosfets.
It worries me when readers tackle probably the most difficult task, at the deep end [PWM]. Mosfets can lead users down a very steep and costly learning curve. I also wince when I see large air cored inductors used in power ccts. I also worry when I see Meg ohm resistors in mosfet gate drive ccts.
Mosfets can be used with high efficiency at switching frequencies above 500kHz, as I have indeed done in other applications.
Some good suggestions have been made by oztules and RossW, particularly re high side drivers and analogue PWM controllers. National instruments produced many books and technical notes, as have Maxim, etc etc.
BTW, the mosfet will turn ON, as a result of the charge pump feeding volts to the gate through the 100ohm resistor. I however see no way of turning the mosfet OFF. the propsed transistor with 1M resistors will not ever turn the mosfet OFF.
I am new to this forum, however I have a lot of experience elsewhere, and I am feeling my way a bit again after forced excile.
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Hi, this is a first attempt at this type of circuit. Funding to order gate driver IC’s will be available within the week.
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2041244_-1
Thank you to everyone for your time and efforts.
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Burnit,
Hi, this is a first attempt at this type of circuit. Funding to order gate driver IC’s will be available within the week.
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2041244_-1
I too have been looking for a way to high side drive a FET and thought this IC might provide a solution for the isolated drive voltage and fast switching required, but after looking at the spec. sheet it appears to only provide the switching. You will still have to have an isolated voltage source to supply the driver IC. Does anyone know of a IC that will do both? Good luck on your project!
Jim
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Hi Burnit,
I have just looked a bit more at the cct you posted, and if the back emf developed by the coil becomes sufficient, then this will push the mosfet source voltage higher. This will then reduce the effective gate to source voltage to a point where the mosfet will no longer be held fully on.
To have low tri-state and conduction losses, mosfets need to be switched fast and with authority. This opens another can of worms with RFI & EMI radiation from wiring etc.
The challenge will test your patience.
Gordon.
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Hi, I redrew the circuit hoping it will be easier for me to explain.
Starting at the bottom: the PMA charges to input capacitor. I have tested the PMA just charging a capacitor. The capacitor charges up very fast and reaches 50 volts in a very short period of time. Because I am just charging a battery I do not believe a capacitor is necessary at the output before the battery, but it can be added if required.
The inverting comparator at the top is needed to enable the system and will disable the system when Vin falls below Vref. Fan out of the comparator should be able to drive two gates.
When point A is high the nand gate oscillator and the voltage multiplier will generate 24 volts across the voltage divider and the second nand gate oscillator will toggle the transistors and create signal Vgs to turn the MOSFET on and off. ( This is the part of the circuit that needs improvement)
The buck converter will continue to function until Vin is below Vref.
I have tested all the parts of the circuit separately and they do function. I am currently constructing the two nand oscillators on the proto board to try to determine if they will generate Vgs. Once I have the Vgs signal then I can add the MOSFET and test with the PMA.
A micro controller can be added after I have a basic circuit working, it will make the algorithm easier to develop once I am able to observe the affect the buck converter has on the PMA.
Thank you for pointing out possible problem areas , it is good to have options. I am just working on one problem at a time. Thanks again.
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I still don't think you're "getting" a critical thing.
The voltage on the gate is actually irrelevant.
It's the voltage on the gate *WITH REFERENCE TO THE VOLTAGE AT THE SOURCE* that will turn the FET on.
So, if you have 50 volts at the rectifier output (point (C) on your diagram), the drain will be at 50V.
The source will be at (lets say) 12V, when the FET is off.
So your charge pump makes 24V. OK. Fine, you hit the gate with that 24V, and at that instant Vs=12, Vg=24, Vgs=12 and the fet starts to turn on.
AS it turns on, the 50V on the drain starts appearing on the source. So it is now ramping from 12V up "towards" 50V. In super-slow-motion... source starts getting power through, it's now at 13V. Still 24V on the gate, Vgs now 11V. FET still switching on, source now 14V, gate still 24V, Vgs now 10V, FET still switching on, source now 15V, gate still 24V, Vgs now 9V, FET may still switching on but not so hard... source now to 16V, Vgs only 8V.... at 20V on the source, Vgs is now only 4V - you see what's happening??
This is ALL because you're driving the gate with a ground-referenced signal, not a source-referenced signal.
The design is fundamentally flawed, and NO amount of fluffing about with it will make it work "properly"
Similarly, turning it "off", as has already been stated - a 1 megohm resistor will bleed charge off quite slowly. It certainly won't be DRIVING the FET off. There's a reason this type of circuit isn't used in production. It just doesn't work.
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Hi, thank you, I now understanding what you are saying. Does a gate driver IC solve the problem?
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2041244_-1
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Hi, on page 22 and 23 there seems to be a solution. Vcc would be replaced by the PMA?
Comments welcome.
http://www.irf.com/technical-info/appnotes/an-978.pdf
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Hi, on page 22 and 23 there seems to be a solution. Vcc would be replaced by the PMA?
Figure 24 looks pretty close to what you want.
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Hi, this is a first attempt at this type of circuit.
I did find a paper that does cover charger design.
http://www.ti.com/lit/ml/slyp089/slyp089.pdf
At the beginning it does explain why a p channel mosfet is preferred for this type of circuit.
Thank you for the help it is really appreciated.
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Hi, the circuit is from the .PDF file. I am not sure if it will address the problem that rossw has pointed out. Searching for circuit to create Vdr, maybe a charge pump can be used.
Comments welcome.
http://www.usna.edu/EE/ee320/Supplements/dcdc5_driver.pdf
I have ordered IR2117
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I am not sure if it will address the problem that rossw has pointed out.
It's still ground-referenced, and inherently will suffer a plethora of problems related to the difference between system ground and FET Source.
As you say, more-expensive and slower P-channel FET would overcome those problems but leave you a different bunch :)
Proper high-side driver is the real answer. Or, isolated supply and perhaps opto-isolated control of your oscillator.
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Or, isolated supply and perhaps opto-isolated control of your oscillator.
That is propably the easier way compared to the signal transformer. Isolating DC / DC converters of suitable power can be had for under 10$, for example digi-key has loads of those parts.
I actually ordered a few of those, when desperation dug into my own mppt project with signal transformer problems. But eventually I was able to get it to work before the converters arrived.
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Hi, the IR2117 have arrived and I completed all the high current connections of the buck converter. Using a Zener diode as Vcc to power just the nand gate oscillator I was able to illuminate a LED with a quarter turn of the PMA. Not great results but it is a start. I have to test the IR2117 with the oscilloscope to determine if HO is oscillating. I wired the test circuit and used a 12 volt halogen light as a test load and spun the PMA manually. The PMA was very easy to spin until the MOSFET turn on, then I was unable to spin the PMA. I believe the MOSFET is not turning off. My concerns are there is a lot energy stored in the input capacitor and I do not want to harm my oscilloscope. Are there any points I should avoid when testing the circuit????? The chassis ground and each channel ground are a the same common point, is there a safe method to use when testing the circuit with the scope? Comments welcome.
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Not a valid youtube URL
Hi, I changed the load to a watt 12 volt light. The video shows the LED on the right then the load lights up. The PMA is very hard to spin.
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Burnit, could you please make a bit higher resolution schematic so I can read the values and net names ?
Thanks,
boB
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http://web.mit.edu/6.131/www/datasheets/float_drive.pdf (pg. 16 and 17 show circuit)
Hi, I tried to increase the size of requested items. I use the key board control key and spin the center mouse wheel to magnify the image. I finally had time to test the circuit with a oscilloscope and found the oscillator is working but the gate driver is not firing and the MOSFET is passing current that is shown in the video with out being turned on. Today I am going try to get the gate drive to fire and replace the MOSFET. I did find the application sheet for the IR2117. I will report results when available. Thank you for the help I am receiving.
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Ahhhh... Much better !
Those IR21xx parts are very nice. My only problem with them is that they don't have a very high Vcc rating. i.e. usually around 20 volts or less.
Just have to be careful not to exceed their maximum ratings.
boB
PS, nice app note. I don't think I'd seen that particular one from IR before.
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Hi, I found one problem. The nand oscillator is only putting out a 5 volt timing signal. The IR2117 has a input low voltage lockout. I have to increase the voltage of the timing signal.
I guess not all 4000 series are the same, thing do change. The new used scope works well, it is fast, gives to much information and has to many buttons but I am happy to have it.
From the application notes it looks like the IR2125 is designed for a 12 volt battery charging circuit. The IR2117 is designed for resistive loads. I am proceeding with what I have. I will be happy if I can just get a MOSFET to trigger at this time and I will post results when available.
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Hi, I found one problem. The nand oscillator is only putting out a 5 volt timing signal. The IR2117 has a input low voltage lockout. I have to increase the voltage of the timing signal.
From the application notes it looks like the IR2125 is designed for a 12 volt battery charging circuit. The IR2117 is designed for resistive loads.
I haven't looked at the application notes for your driver - but it would seem "likely" to me that it has a degree of input waveform shaping, and doesn't require the super-fast rise and fall times you need for the fet itself.
Therefore, it MIGHT be simple and easy to either use a diode/resistor pair to generate a 0.9-12V approx waveform from the IC output to the driver chip, or a single-transistor as a open-collector buffer to give you a nearly 0-12V drive for your IR21xx chip. The relatively slow rise-time shouldn't be a problem to the fet, as the driver should square it up?
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Hi, photo shows input timing signal from 555 timer and output (HO) of IR2117. The MOSFET is not connected. I had to connect Vs to ground. Duty cycle is a little greater then 50%.
The application notes says that the logic ground and power ground should not be connected but their diagram shows they are connected, I find this very confusing. I am not sure where to generate Vcc? Comments welcome.
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Hi, I may have found a solution to provide an isolated Vcc. I may not sure if it work, comments welcome. I will post results when available.
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Might try a 7555?
G-
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Hi, The photo displays the Vs wave form on top and the IR2117 trigger input on the bottom. I am using switching diodes because I do not have any fast recovery diodes.
The only way I could get the MosFet to turn off is to connect Vs from the IR2117 to ground. Control signal is 10 kHz and I am using bench power supplies and a 12 volt light for a load.
I am making progress.
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I'm no expert at switching, but i've made one once, and i didn't get the signals stable before i added a ferrite bead after the gate resistor, close to the Gate of the fet, and a diode from the gate to the ground to protect the gate from reverse currents.
To get the fet to turn off properly, put a 100k resistor from the gate to ground. :)
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What does Vgs look like, and Vds. Is the bottom trace Vgs or is it the input to the driver.... what does the output at the driver look like compared to the Vgs trace.
It looks hot and scary that top trace.
..................oztules
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It looks hot and scary that top trace.
I don't think I ever saw anything quite like that before.
G-
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It looks hot and scary that top trace.
I don't think I ever saw anything quite like that before.
G-
I was thinking the same.. wow.
I am making progress.
I'll have to take your word on that.. What were you expecting there?
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It looks hot and scary that top trace.
I don't think I ever saw anything quite like that before.
Looks to me like a fair whack of AC on there. The CRO has been in AUTO trigger and it's a bunch of sweeps superimposed.
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Hi, I have been trying to find material on how to use the scope. The channel grounds are the same points and all the channel grounds are the same as chassis ground. It is the only way I could get the sweep to show on the display.
When I try to measure the circuit using a DC channel mode the power supply over current protect feature on the bench power supply kicks in and the power supply shuts down. What is the correct way to use the scope? It is a Tektronixs 2246. Any help will be greatly appreciated.
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Not sure if this helps but.
http://aries.ucsd.edu/najmabadi/CLASS/COMMON/XYZ-Scope.pdf (http://aries.ucsd.edu/najmabadi/CLASS/COMMON/XYZ-Scope.pdf)
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Hi, thank you. I have reviewed the material. The only thing I can think of is the ground of the scope is at a different potential than the ground of the power supply. I have one scope that lost the trace during testing and I am not sure if it was because of age and just happen to stop working at the same time I was testing the circuit or the testing of the circuit was the cause for failure. I am trying to avoid having a repeat of scope failure. Should I connect the scope chassis ground to the power supply chassis ground? Comments welcome
on page 45 it says the scope should have the same ground as the circuit being tested.
Is that the power supply chassis ground or the -V of the power supply? The power supply has three terminals, V+,chassis ground, and V-, maybe I am connecting the power supply wrong.
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photo of power supply
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Hard to tell from the pictures.
Take your multimeter.
Disconnect outputs from your power supply. Set it for about 10V.
Measure from + to - and tell us if it's 10V or 20V.
Measure from gnd (earth, the centre banana socket) to + and -.
Is there any voltage from ground to either? If so, how much?
If it's as I *SUSPECT* it is, you'll have 10V + to -, and nothing gnd to + or -.
If thats the case, you should jumper gnd to - in this case.
(Many of these power supplies had a solid jumper link installed between the banana sockets)
Now take your multimeter. Make sure the CRO and power supply are plugged in the same outlet.
Measure from power supply gnd/- to CRO ground. There should be no voltage.
Check from power supply + to CRO ground. There should be 10V.
Check ohms from gnd/- of the power supply to CRO probe ground. Should be under an ohm.
If that's all as indicated above, then you have a "normal" setup.
You CRO probes ground can go to the "ground" (0V) part of your circuit *ONLY*
If you're in doubt, you can connect a 10R in series with the cro probe ground to wherever you intended to put it.
10 ohms won't make any difference to the CRO readings - which should have a minimum input impeadance of 1M, and probably 10M. But if you try to "earth" to something that's 12V or more away, your 10R will smoke rather than the CRO.
(I once installed such 10R resistors in the little ground wire from the probe, when students kept blowing sh!t up)
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Hi, I found a manual for the power supply on line.
http://cp.literature.agilent.com/litweb/pdf/06284-90002.pdf
It has rear panel jumpers. I have to review the manual to determine what is the correct way to set the jumpers up. I did some measurements as instructed and found
Measurements from front panel, set for 10 volt output:
+ to - (10 volts)
+ to Gnd (0volts)
Gnd to - (-10volts)
It looks like the real panel jumpers affect the output of the front terminals.
Not sure how to set up jumpers on the rear panel, if anyone has experience with this type of power supply comments are welcome
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Hi, project update, thank you rossw, the power supplies are back on track.
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Hi, the power supplies have new rear panel terminal configuration. I am unable to increase the voltage at Vin of the buck converter. I may still have rear panel connections mis-wired.
The top wave form is Vin of IR2117 and the bottom is Vs after mosfet.
I still have to add the fast recovery diode, it should be here in a few days.
The wave form at Vs shows the mosfet is turning on and off. Comments are welcome.
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Hi, I managed to resolve most of the problems with the proto circuit when using the bench power supplies. They were mainly caused from the power supplies and I had the new oscilloscope probes set to x10.
I still have to resolve one problem. The output from the 555 oscillator has a severe ringing that is transferred to Vs of the mosfet. But the boot strap appears to be working with the Vs from the IR2117 connected to Vs of the mosfet and the mosfet is turning on and off.
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Hi, video shows manual operation of PMA and buck converter to a resistive load.
The mosfet is turning on during the off cycle of the IR2117. Is there a solution to this problem??? Comments welcome.
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Hi,
I found a reference to the problem on page 8 and 9.
http://www.nalanda.nitc.ac.in/industry/appnotes/IR/ASSETS/TECHDOCS/APPNOTES/An978.pdf
It recommends increasing the boot strap capacitor to a valve greater than 0.47 uf. I will post results when available.
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Greetings, I added the larger caps to the boot strap and the ringing is still there but only noticeable at lower RPM’s.
I am still using the 555 timer. I increased the duty cycle to 80% and inverted the output so the duty cycle at the input of the IR2117 is 20% high. I connect a 12 volt 50 watt light and spinning the PMA manually I was able to illuminate the 50 watt light with relative ease. Wow, a shorter duty cycle made all the different. The PMA was much easier to spin and even maintained momentum for a short period when I stopped spinning the PMA.
Without the buck converter I was unable to illuminate the 50 watt load under manual operation.
I am still using the bench power supply to power the IC’s.
Performance has definitely improved.
I still need away to control the duty cycle at different PMA RPM’s and find away to power the IC’s from the battery or PMA. Next step is to try charging the battery. It maybe time to start thinking about adding a micro controller. Thank you for all the suggestions.
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Greetings, I added the larger caps to the boot strap and the ringing is still there but only noticeable at lower RPM’s.
I am still using the 555 timer. I increased the duty cycle to 80% and inverted the output so the duty cycle at the input of the IR2117 is 20% high. I connect a 12 volt 50 watt light and spinning the PMA manually I was able to illuminate the 50 watt light with relative ease. Wow, a shorter duty cycle made all the different. The PMA was much easier to spin and even maintained momentum for a short period when I stopped spinning the PMA.
Without the buck converter I was unable to illuminate the 50 watt load under manual operation.
I am still using the bench power supply to power the IC’s.
Performance has definitely improved.
Hopefully, performance will improve ever time you play with this stuff. Expect to
blow it up from time to time while fooling with it though.
So, is the light changing brightness from you changing rotation speed ? It doesn't look
like the duty cycle is changing there but the voltage is changing. How about changing
the duty cycle and keeping the rotation constant with a motor or something ??
That's a cool thing to see working too.
I still need away to control the duty cycle at different PMA RPM’s and find away to power the IC’s from the battery or PMA. Next step is to try charging the battery. It maybe time to start thinking about adding a micro controller. Thank you for all the suggestions.
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Hi, The pulsing from the light is caused from manual method I am using to the spinning the turbine. It does not allow for continues rotation, I am forced to release the belt drive pulley after a half a revolution, but it does increase the RPM to illuminate the 50 watt load. I am searching for away to supply power to the IC’s from the battery bank or from Vin.
This turning into a real learning experience. Getting the Mosfet to turn on and off with a resistive load is just the first part of the project, the circuit does not operate using a battery for a load at this time.
Using a shorter duty cycle does require less torque to spin the PMA. I am still trying to understand the MPPT algorithm.
I am searching for a circuit that will adjust the duty cycle as the RPM increases.
Comments welcome.
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Hi, The circuit is working with a resistive load.
1. The mosfet source is connect to the high side of the load. The mosfet is a IRF510.
2. A IR2117 with bootstrap is being used and is referenced to Vs so the bootstrap capacitor voltage can be charged high enough to turn on the mosfet.
3. A 555 timer is used to control the IR2117 @ 10kHz with a Vcc of 12 volts.
4. A permanent magnet alternator is used to supply Vin and can range from 0 to over 200 volts depending on the permanent magnet alternators RPM.
5. A bench power supply is used to supply power to the IC’s. This will be changed later.
The problem is :
When the resistive load is replace with a 12 volt battery the circuit does not work.
I do not understand why the circuit will work for a resistive load and not with a 12 battery as a load. Any suggestion will be greatly appreciated.
http://www.ti.com/lit/ml/slup169/slup169.pdf
on page, 26 Figure 29 maybe the solution. What value should Dz be?
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"The problem is :
When the resistive load is replace with a 12 volt battery the circuit does not work.
I do not understand why the circuit will work for a resistive load and not with a 12 battery as a load. Any suggestion will be greatly appreciated."
What part does not work. Is the fet being pulsed but not turning on or is there no pulse, or have you not enough output voltage to drive the battery perhaps... ie if you have 50% pulse width and the input is not over 26v, youmay not have the output above 12v to charge the battery as a load?
..............oztules
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Hi, when was testing with the resistive load if there was any charge on the large input capacitor the MosFet would never turn on. The voltage of the input capacitor , Vin, would continue to increase as the PMA was rotated. The only way I could get the MosFet to turn on would be to completely discharge the input capacitor then the circuit would work, the circuit would turn and off as I manually operated the PMA.
When the battery is used for the load the MosFet never turns on and the large capacitor voltage, Vin, just increases. There is no output pulse from the IR2117.
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I have never used that kind of circuit before.... that said, you sound like the bootstrap is not working. I suspect that it is because the charge pump cannot work on smooth DC. By discharging the cap, the pulsed DC input gets it going, and once running the pulses come from the loaded open and close interaction. (D S open closed) or, CBST discharging into the gate via VB
With the battery connected, at start there is no pulsing voltage to get the vs vg voltage needed. VB must come from Vin being 12v ( or whatever uvlockout is) above b+
Dz could be 14v
What is the VB to VS differential when you cant get it to fire. Is it above lockout?
To test this, use an isolated supply to VB and VS on the high side driver, and see if that runs it. If so, your not getting pulses to the charge pump on at start, only stable DC< 25v or so.
Can't have a charge pump without voltage fluctuation.
With the charge pump not working, the pm will only keep charging the filter cap up.... until if vb is 12v or so above vs, it should get going.
I have never bothered with driver IC in high side only use, but you should be able to find where the voltage is not, and work from there.
If supplying isolated voltage from VB to VS, does not get the driver going... perhaps the driver chip is toast.
If you still can't get it going, try a toroid driver, just to get it a feel for a working circuit, and then work backwards to your exotic chip system.
Another alternative is to use ( when all else fails) some of the pm ac to drive a small transformer to make a truly isolated supply, and drive the fet directly with this.... silly but very stable.
..............oztules
Edit: and lets assume you have Dstart around the right way :)
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Hi, I exchanged the IRF510 with a IRF540 and I am unable replicate the results shown in the last video. It is a puzzling situation. It may require a different bootstrap capacitor or some other solution. I am unable to continue until a solution is found. The circuit will function with a lower load but does not work with 50 watt load. The oscilloscope shows the IRF540 starts to turn on then very quickly turns off, then the Vin gains magnitude and the 555 timing signal shuts down. Comments welcome.
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Hi, I was able to find all the needed parts to make all the required connections to interface the circuit to a 12 volt battery. I am using to bench power supplies, one to power IC’s and the other for Vin.
I had just a LED and 22kohm resistor from the mosfet Vs to ground and the mosfet was turning on and off.
With a capacitor at the output of the circuit no current would flow into the battery. I removed the capacitor and I was able to measure 0.14 amps flowing into the battery.
I had attached a variable resistor to the 555 to be able to test different duty cycle, I adjusted the variable resistor to low and the 555 fried, so I have to purchase some replacements before I can continue testing. I will post more test results after I replace the 555.
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Hi, I have verified that using a isolated power supply for the gate drive circuit will turn the N channel mosfet on and off in a Buck circuit configuration with a 12 volt battery as a load. I configured the gate drive circuit with a 555 time and used a Schmitz triggered nand gate as a inverter. The 555 timer was configured with a variable 1 meg ohm pot so the duty cycle could be changed. The shorter I set the duty cycle the easier the PMA was able to spin and produced a very high voltage at Vin. Positive current was flowing into the battery. Under manual operation the best I could achieve was 0.7 amps flowing into the battery. The circuit will definitely benefit from using a microcontroller to adjust the duty cycle. At this time I starting to work on paralleling the mosfets and adding a microcontroller to the system. Comments welcome
This is the part I find confusing:
When comparing the waveforms of the two gate driver circuit’s the circuit without the IR2117 triggers the mosfet all the time.
Video without IR2117 in gate driver circuit:
mosfet Vs is top waveform:
The circuit using the IR2117 only triggers the mosfet when the PMA provides a input voltage.
Video using IR2117, bottom waveform is mosfet Vs:
Waveforms in both videos are measured at the same point.
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Greetings, using a isolated power supply and FOD3180 does work. I am using a blocking diode between the inductor output and the plus terminal of the 12 volt battery. The gate driver is triggering a N channel IRF540 in a Buck circuit configuration and is charging the battery, current about 1 amp. Then I replaced the battery with the 50 watt halogen light and the circuit was able to illuminate the light after I adjusted the duty cycle, current max about 4 amps. I was manually operating the PMA. So far this is a very happy day. The next step is to drive the PMA with the drill press to determine how the circuit behaves at a higher RPM.
Chapter 4. page 69
http://etd.ohiolink.edu/view.cgi?acc_num=akron1320692738
Isolated power supply with FOD3180 gate driver. N channel Buck converter using a IRF540 mosfet. Bottom wave form is gate of mosfet, top wave form is source of mosfet.
Input voltage max about 40 volts. Output current varies depending on duty cycle. Circuit still needs improvement but it is working. Input voltage is from a permanent magnet alternator and is being manually operated. Comments welcome.
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I think you were smart to start using the FOD3180 driver !
it's a great part.
boB
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Hi, Vee is connected to Vs of the mosfet and rides on Vs of the N channel mosfet. So it is functioning like the bootstrap capacitor of the IR2117 but the FOD3180 will work with both a resistive load and will also work as a battery charger. I am not sure if that makes any sense. Basically I could only get the IR2117 to work with a N channel mosfet with a resistive load. The FOD3180 and isolated power supply will work with a N channel mosfet with a resistive load and as a battery charger. I hope that helps anyone that is going to try a similar project. I know, as clear as mud. ???
I am now working on adding a snubber to dampen the ringing. Any suggestion will be greatly appreciated, comments welcome.
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I think you were smart to start using the FOD3180 driver !
it's a great part.
boB
http://www.midnitesolar.com/pdfs/classicDevUpdate3.pdf
Not a fan of art deco but I wish I could afford one of your controllers. Very nice!
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Yep. That's it.
BTW, it uses that same FOD3180 driver.
boB
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I am now working on adding a snubber to dampen the ringing. Any suggestion will be greatly appreciated, comments welcome.
In a nutshell: Really fast Schottky diodes and several low ESR caps on both the output and input. At the output, place them as close to the coil and Schottky cathode as you can get them. At the input, as close to the tranny's drain as you can get them. Ground heavy and nearby, with the common point ideally at the cathode of the Schottky.
The more solid your input/output rails are, the better, as less power will be lost by radiation. The input is sometimes neglected somewhat, but is also important, as you need a solid source for nice sharp, hard pulses at the input, not just a place to catch them at the output.
I notice in the schematic you posted, there aren't even any caps in the output. You'll just be wasting your time sending those spikes up the battery leads - the inductance of the cables will absorb a fair amount of power, effectively making little more than a crude antenna. In all honesty, this is where most of the ringing you're witnessing is currently coming from.
Other tidbits that come to mind:
It's going to be difficult to get rid of the ringing with any real effect with the breadboard in the mix, thanks to parasitic everything that's inherent to using such things. :-\
If you still need the versatility of the breadboard for further refinements, you can set up the "grunt" components on a more permanent fixture such as perfboard so that you can make the power path traces heavy and close together, along with your strategically chosen and placed filtering caps. This should help significantly.
The other thing that will greatly affect performance is the length of the run from the MOSFET driver to the gate. The longer this is, the more parasitics you will have, the slower the effective slew rate will become, and the more power you'll waste in the tranny as heat. Drive it short and hard - ultimately, everything from the gate driver on needs to be as close together as possible to get maximum efficiency.
Hope this helps some. ;)
Steve
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Hi, I completed fabrication of analog MPPT test circuit. Video shows verification of selectable duty cycle with fine adjustment of each for each selected duty cycle, 10% to 50%. Next step is to test with PMA and battery test load. I am hoping I did not damage the mosfets when I solder them in the circuit.
Thank you for all the help I have been receiving, circuit should help me better understand requirements for MPPT algorithm.
I connected four IRF510 in parallel, this is a first attempt and is just for the learning experience of paralleling mosfets. My PMA has inputs and outputs on each stator so I can change the internal resistance of the PMA. The variable duty cycle of the circuit will aid in testing of the different internal resistances of the PMA. I will post results when available.
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Hi, just a quick video showing test setup. With the PMA at 200 RPM the input voltage was 170 volts, 1.5 amps input current, 12.34 output voltage, and 0.3 output current. Mosfets measured 82 degrees Fahrenheit. The circuit needs major improvements. The input capacitor is only rated for 100 volts and I have to check my inductor calculation. So there are major loses and the buck circuit is not working as it should but the test fixture is working. I am using a 12 volt deep cell for a test load. It does show the control circuit is working and the mosfets are turning on and off. It is a start. Comments welcome.
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With the PMA at 200 RPM the input voltage was 170 volts, 1.5 amps input current, 12.34 output voltage, and 0.3 output current.
So there are major loses and the buck circuit is not working as it should but the test fixture is working.
If I assume 170V RMS or DC input, at 1.5A thats 255 watts in.
12.34V @ 300mA out is 3.7 watts out.
Where is the other 250 odd watts going??
SOMETHING is getting very hot. Or there's something you're not telling us..
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Hi, I have not been receiving email notifications when anyone posts a response to my project. I found intermittent contacts in the test circuit and I found a few of the DMV’s were not working correctly and had to replaced. I changed the input capacitor to a much larger value and the circuit appeared to be working for awhile and then stopped. I think what happened is I exceeded the Maximum Power Dissipation value of the mosfets, I was only considering the Continuous Drain Current value as the limit. I also found some information about paralleling mosfets that said each mosfet should have it own gate resistor, I was only using one resistor for all four mosfets. I think the reason for the earlier high voltage reading is because I exceeded the input cap voltage limit and the dielectric layer was destroyed and created a path to ground at the input, but it is just a theory.
I am currently replacing the mosfets with IRF540’s and each will have it own gate resistor. I will use the Maximum Power Dissipation value to determine the current limit for the circuit and I will try not to exceed that value.
The circuit is close to working it just needs some find tuning. I am trying to report my progress as complete as possible but my limited experience is making it difficult. I greatly appreciate all the suggestions I am receiving. I will post results after the repairs are made. Thanks again and comments are welcome.
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Hi, I removed the four IRF510 and checked each one and they all passed. During that time I found a intermittent contact at the ground post going to battery. At this time I believe this problem was the main reason for all the other problems. So the circuit status is not as hopeless as I previously thought. It is always the little things. The shame is on me. I was also able to trace the source of the voltage spikes in the control signal back to the 555 timer.
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Hi, video update of project
I was baking DMV's when I was trying to measure higher currents for long periods of time. I added some analog current meter to address the problem.
12 coils per phase was creating very high voltages at the input. I reconfigured the stators to 4 coils per phase. Open circuit voltages was about twice the amount of the measured values at Vin when using the circuit.
New test data;
rotor speed 500 RPM
Vin 40voltsDC
Iin 3amps
Vout 12voltsDC
Iout 6amps
Duty cycle 50%
Stators 4 coils per phase
stator resistance < 1 ohm
Circuit temp 82 degrees Fahrenheit
Inductor temp 170 degrees Fahrenheit
I need a better inductor.
I changed the inductor to the larger air core and values improved. About 60 watts at the input and about 60 watts at the output. The inductor temp was much cooler. Measured values are just ball park but I am starting to have better understand all the relationships involved. At this point I may have better performance at a lower switching frequency.
I purchased some 500 volt 100 uF caps, IRF830’s, and some toroid 5 amp continuous inductors. I plan to parallel 4 of the caps, 4 of the mosfets, and 3 of the inductors. The new switching frequency will be about 6.5 kHz. The manually selected duty cycle seem to be a nice function and will I have to recalculate the resistor values for the 555 timer and duty cycle selector switch. I not sure how well it work, but I will post results when available.
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Hi, I configured the PMA using just 2 stators to form a 3 phase star, 8 coils per phase. Phase to phase resistance = 9 ohms.
Rotor RPM_____Voc DC
100____________15
200____________30
300____________45
400____________60
500____________75
Rotor RPM_____Vin DC____Amps in____Amps out
100____________16.5______? _________0.2
200____________27.3______0.2________1.0
300____________28.8_____ 2.0_________5.0___Vout = 12.8Vdc
Free wheeling diode temp = 82 degrees F
50% duty cycle
test fixture limit 300 RPM using load
Vout = 12 volt deep cell test load
measurements ball park , 60 Watts appears to be the limit of test fixture under load.
I have to remove one stator and rotor and then I will be able to road test. Search for ideas on how to limit voltage to 100 volts at the input to protect circuit. Comments welcome
I am do not know how to measure current with a O-scope. I am researching the method.
Maximum current output without using the circuit 2 amps. The circuit is definitely is a benefit.
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I am do not how to measure current with a O-scope. I am researching the method.
One way is to use it to measure voltage across a known low resistance (shunt) like a shunt in any ammeter. Then you just do some math E=I*R or divide the violtage by the resistance to get amps.
A 1 foot hunk of #10 solid copper wire will drop 1 millivolt per amp of current through it. Good enough for comparisons as is and could be calibrated using a known good ammeter.
For those unfamiliar with the shorthand:
E=Volts
I=Amps
R=Resistance in Ohms
Probably other methods but this will work and is simple to do.
You could make a lookup table once you set up the circuit to eliminate constant arithmetic operations in use.
Tom
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Hi, thanks for the info. When I started this project I knew nothing about it and now I know next to nothing. I am making progress.
Thanks again and enjoy the day. :)
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60 Watts appears to be the limit of test fixture under load
In my experience, that's about the limit for efficient operation of a non-synchronous converter. Much higher than that and losses start to really add up in the diode.
Synchronous converters are a bit more of a challenge, but can provide more power at the output.
You are correct in that the test layout is also a limiting factor. You have parasitic everythings in there - Inductance, capacitance, you name it. It all adds up and works against you.
I can't emphasize enough that everything in the "grunt" portion of the circuit needs to be as close together as physically possible. A 3 inch wire here, 4 inch there, doesn't seem like much, and for DC it isn't. But at the switching frequencies that converters typically run at, they become inductors and cause switching pulses to "soften" and all kinds of other havoc. In fact, get enough inductance in the wrong area, and it will leave you scratching your head wondering why you have a pile of popped MOSFETs. :(
By close together I mean 1/4 inch. And heavy. At the power levels you're after, you have to minimize the losses everywhere you possibly can, or you're working backwards against yourself.
Your layout reminds me of my first few attempts at making a converter as well, and they all failed, miserably. Once I understood the importance of physical proximity and layout, the magic smoke stayed in and the power started flowing.
For learning purposes, there is inevitably a certain amount of rat nest in the mix. The sooner you can get away from it though, the better. For an idea of how it's typically done, examine a manufactured buck converter. You will notice that the 3 power handling components (tranny, inductor, diode) are very close together. VERY close. And the caps are not far from them either. Which brings me back to caps.
And caps. Caps, caps, and more caps. Caps on the input. Caps on the output. Low ESR caps. Right next to the switching components. Lots and lots of caps. It may seem like a couple 4700uF elecrolytics would have more brass than a dozen or so of their low ESR 47uF brethren, but at those frequencies, the inductance in the leads and plates of the 4700s become a significant issue, and reduce (if not just about eliminate) their effectiveness. Larger caps are ok to have in the mix, in fact I recommend that you keep them there. Just move them "further out" away from the switching components and use the smaller, more solid counterparts up close and personal with the switching components. You'd be amazed at how much this will improve performance. I usually use a few different values too - my theory there is it "detunes" the rails, and helps suppress and absorb ringing and pulses across a wider spectrum. Might be overkill, but I do it anyway.
It's not so much the actual switching frequency either, even though this of course plays a significant role. The switching frequency directly affects losses because the higher it is, the more often the transistor is in "linear" mode, which is essentially resistive, which translates to heat. But that's only part of the equation. The slew rate (time it takes the transistor to transition from fully off to fully on and vice versa) is also a significant contributor to the amount of power lost as heat in the transistor. The more time it takes to transition, the longer the transistor stays in the linear region on each cycle, which translates to even more heat.
Buck converters are finnicky little bastards, and it doesn't take much for the losses to add up and make them much less effective than they could be.
And keep things close together! (Think I already mentioned that!) :D
Steve
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Hi, I started fabricating a new board and I will try to include all the suggestions. I am trying to increase the input voltage to as high as possible. I found some problems with the value of the bridge rectifiers and I am ordering new parts. I am using 4.7 ohm on the gate resistor of the mosfet to keep the transition time low. Using the analog current meters to measure input and output current is working well, I was baking the DMV’s. I am using a infrared thermometer to measure the temp of the circuit board, it does help trace down problem areas on the circuit board.
Because the project is for a VAWT and the RPM’s are very low I purchased a F&P.
F&P open voltage measurements.
12 coils per phase, 3 phase star, phase to phase resistance 37 ohms, load 450 volt 470uF capacitor.
RPM________Voc DC
100_________130
150_________180
200_________230
250_________280
300_________330
just ballpark measurements, when circuit is operating the input volts equals half of the open circuit voltage.
The output of the stock F&P is very high and safety is a major concern. . Safety first. Watch the end of the video.
I should know more after the first road test which should be within a few weeks. I will start with direct drive and than adjust parameters based on results.
I am not receiving email notification when there is a reply to this topic. I greatly appreciate all the help I am receiving and I will post test results when available.
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CooL video !!
Nice kitty, too.
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Umm... wow man.
So let me get this straight... the arcs you were drawing are directly from the output from the generator? In other words, no step-up transformer or anything like that?
If so, you're looking at a LOT more than 700V there dude haha... Like maybe a couple (or better) orders of magnitude more? :o
I may have missed something... and I'm thinking that's probably the case, but it doesn't appear that the wiring would be able to keep all that inside.
So that being said, what DID I miss? LOL
Steve
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Hi, I found the video on you tube, I did not make the video. The F&P generates about 1 volt per revolution. It has a very high voltage output with low current. Because my VAWT is very slow I am trying it with the Buck converter. I purchased some new parts that should increase the input voltage limit to 450 volts and the output current limit to 15 amps. I am not sure if it will work. I added a 5 amp fuse at the input and a 15 amp fuse at the output of the circuit. The F&P is very common on the Pacific side of the planet and is starting to show up in the states. I will be testing the F&P using direct drive so as long as the rotor RPM remains under 900 RPMs it should work with the circuit. Remember this is a experiment and a first attempt.
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Wow, ok... Just checking.
Sounds like you've got your head wrapped around this pretty well I suppose.
Just be careful man. That there aint no joke! LOL
Steve
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Hi, results from today’s stock F&P and Buck converter tests:
I replace the failed diode with five 3 amp 400 volts diodes and connected them in parallel. After increasing the PMA RPM above 100 the timing signal became unstable and the mosfet and diode array became very hot. Highest temp reading was about 140 degrees Fahrenheit. Then the mosfet or diode array stopped working. I will have to investigate to determine which one or both failed. Before the failure I was able to observe at shorter duty cycles the buck converter stopped converting and was feeding large voltage values into the battery, sometime above 100 volts.
Conclusions from today’s test:
1. The stock wiring of the F&P produces a voltage much to high to be used with a buck converter to convert down to 12 volts for battery charging. The stator should be re-wired so that multiple phase coils are connected in parallel to reduce max voltage output to 50 volts for the max RPM of a turbine. Because of the quality of the materials; the plastic holding the stator together and the time involved to re-wire the stators I believe it is much easier for me to fabricate the PMA using established fabrication techniques.
2. I was getting better results using lower switching frequencies. I will redesign the circuit to operate at around 10kHz or lower. After reviewing component cost and availability I am pursuing 5 amp power module configuration with single timing controller board, so for a 15 amp output would require one controller board and three power modules. I am not sure if it will work.
What I need to find out is as more power modules are connected in parallel can the switching frequency remain constant, or does the switching frequency have to increase because each power module will have its own inductor and connecting the modules in parallel will reduce the inductance and cause the inductors to saturate. I am not sure and comments are welcome.
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Hi, is it possible to use high voltage capacitors in series to divide the input voltage to a more useable level?
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Hi, is it possible to use high voltage capacitors in series to divide the input voltage to a more useable level?
Sort of... Kind of... But it will work way better on the AC side of the rectifiers.
boB
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The stock wiring of the F&P produces a voltage much to high to be used with a buck converter to convert down to 12 volts for battery charging.
One thing you may want to consider here, is what's called a "forward converter". Essentially, it's a high frequency transformer in a push-pull configuration on the primary. There are advantages and disadvantages to going this route, but you might gain some efficiency at the power levels you're working with by going this route. One of the harder things to overcome (at least in my experience messing with them) is the kick-back from the transformer into the MOSFETs. It can be difficult to tame, and results in a lot of magic smoke if this little detail's requirements aren't met. :-\
I was getting better results using lower switching frequencies. I will redesign the circuit to operate at around 10kHz or lower. After reviewing component cost and availability I am pursuing 5 amp power module configuration with single timing controller board, so for a 15 amp output would require one controller board and three power modules. I am not sure if it will work.
You can parallel buck converters, just as you can any other kind of power supply, given that the load is balanced between them. This can be tricky to do from a DIY perspective, simply because tolerances are generally a little bit "sloppier". Just an inherent issue in the "manufacturing" process (doing it by hand).
There are a few methods used to counteract this. One, is to synchronize the converters in a master/slave configuration, where there is one controlling chip that does all the monitoring/feedback/duty cycle operations, and the slaves just do the dirty work. I have a power supply that is set up in such a way here at the house, it has 5 of 6 modules installed, and is capable of 100A @ 13.8V. Each module carries 20A, and the outputs are all tied together on a buss. There is a single conductor that jumps from module to module to provide the switching control for all of them.
Another method used where the DC waveform needs to be smoother but increasing switching frequency isn't practical, is to drive the modules in a "ring". Each module switches n degrees out of phase with the next, evenly spaced out with each other. The result is a higher effective switching frequency, with a lower actual frequency, each converter carrying it's portion of the load. This is probably the most difficult to implement, as you also need the special chip that controls the phases. They are also typically synchronous in nature (MOSFET on both the high and low side, rather than a MOSFET and a Schottky diode). Haven't built one myself, too complex for my blood. :D
What I need to find out is as more power modules are connected in parallel can the switching frequency remain constant, or does the switching frequency have to increase because each power module will have its own inductor and connecting the modules in parallel will reduce the inductance and cause the inductors to saturate. I am not sure and comments are welcome.
See the above. It really depends on the type of converter you intend to use. Directly applied to your current design, there's no need to increase or decrease the frequency "just because". There are pros and cons to going higher or lower, all depends on what your needs are. But remember that at 10KHz, you're going to be hearing a lot of whining coming from this thing, and if it's going to be where you can hear it, it will drive you nuts.
A typical tradeoff between performance/efficiency/noise is 25KHz. That's fast enough to keep it out of audible range, but slow enough that the losses in the transistors/diodes don't get excessive.
All in all, when you first posted about this, I didn't think that your input voltages would be so high, so a buck seemed pretty much on target. It would have been fine for example if you had a 48V turbine, and wanted to charge a 12V bank. Several hundred volts in (or even a couple) is an entirely different animal. At this point, even given your skill set (which is above many), I'd look into the forward converter from here. A properly built module can handle several hundred watts on it's own, and it would be trivial to parallel two or more modules together to handle multiples of that.
As boB loosely alluded to, I too would stay away from the "cap divider" - it's begging for instability, and will bring it's own set of challenges to the table.
Good luck. :)
Steve
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Hi, is it possible to use high voltage capacitors in series to divide the input voltage to a more useable level?
No.
The Capacitors will charge up on DC - you'll get a brief output while there is charging current, then nothing.
If it was on the AC side, before the rectifier, then yes - but why would you? It's a series circuit - current will be the same, voltage will be far less, so *power* will be divided too. (That is, in your sample diagram, if you had say 400V and 1A, at the indicated tap you'd have 100V, still only 1A - so only 100W out from 400W input)
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Something else that comes to mind, although it might take some of the fun out of it, depending on how or what you do with it...
A PC power supply has a good percentage of what you're trying to do already laid out and put together. Inside, the voltage that goes into the conversion section is about 320VDC, across two caps. If you can tame your mill to this general range, you might be able to just get the raw grunt section out of one of these supplies and use it almost as-is.
I don't know for sure how well this would just "plug in" to what you're doing, as I haven't tried anything like it myself, but I have made minor mods to them in the past, such as adjusting output voltages and the like. They can typically handle several hundred watts, so you'd be in the ballpark anyway.
Just a thought.
Steve
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Hi, making progress. I am trying the parallel buck idea. I only have enough parts to fabricate three Buck power modules. It is enough to test with. I still have to route wire connections and fabricate controller board.
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Silly question perhaps - but why are you replicating the 3ph bridge rectifiers 4 times?
Wouldn't one decent one be simpler and cheaper? And one decent one probably more reliable?
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Hi, I have limited knowledge of power circuits. Connecting the input capacitors parallel will reduce the capacitance and possibly increase ripple at the input. When the mosfet is on the inductors would be in parallel and their values would change and create a problem with the switching frequency being used.
The other problem I am having is finding away to limit the input voltage to a value that does not exceed the max voltage value of the parts being used. I am not able to find parts that will output 15 amps. I am trying to install a working system before it snows. The only success so far has been a single buck converter with a 5 amp 13.7 volt output with 1 amp and 70 volts at the input.
By connecting multiple isolated 5 amp max buck converters in parallel I am hoping this will avoid any problems. I have enough parts for 3 power modules and one controller board. It is enough to test with. Corrections to my reasoning are welcome.
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Connecting the input capacitors parallel will reduce the capacitance and possibly increase ripple at the input.
No, caps in parallel add. In series they reduce.
Resistors in parallel reduce, in series they add.
By connecting multiple isolated 5 amp max buck converters in parallel I am hoping this will avoid any problems.
Good luck. It's far more difficult to balance multiple parallel stages than one larger unit.
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Connecting the input capacitors parallel will reduce the capacitance and possibly increase ripple at the input.
No, caps in parallel add. In series they reduce.
Resistors in parallel reduce, in series they add.
By connecting multiple isolated 5 amp max buck converters in parallel I am hoping this will avoid any problems.
Good luck. It's far more difficult to balance multiple parallel stages than one larger unit.
Hi, thanks for clearing up my confusion about the capacitors. What about the relationship of the inductors values and the switching frequency when the mosfet is on?
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Hi, thanks for clearing up my confusion about the capacitors. What about the relationship of the inductors values and the switching frequency when the mosfet is on?
Well, in very broad, general terms - the smaller an inductor is, the higher the switching frequency will need to be for a given energy.
Inductors in parallel will increase their ability to carry current, but inductors in series increase their inductance.
(edit: clarity. Inductors in series increase their collective effective inductance. Each inductor doesn't change)
Higher switching frequencies in FETs makes the drive more demanding, and (generally) the FET spends more time in linear regions - thus increasing its dissipation and reducing overall efficiency.
Everything gets to be a tradeoff.
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Hi, I was able to fabricate some single sided PCBs for the controller and Power Modules. So far I have tested the circuit using a stock F&P radial flux AC motor using a hand crank to manually spin the PMA. I have to drive the PMA with the drill press for more testing.
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Hi, approximate measured values:
RPM = 280
Current in = .7 time 3 I can only measure the current at the input of one buck converter, I am using 3 buck converters. Input Current = 2.1 amps DC
Vin=58 volts DC
duty cycle = 30 %
Vout= 12 volts
Current output = 7 amps
Result obtained using drill press test rig. PMA is stock F&P. I may get better results using a PMA with a higher current and voltage output.
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Seems to becoming along nicely. ?.
Are you reaching the figures you hoped for?
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Hi, I have all the pieces, I just to adjust some of the parameters. There are problems. I have to improve the fine tuning to adjust the duty cycle, it not working as good as the prototype circuit. It is a resistor value problem. At 10 % duty cycle the output signal is not stable. I will make a video showing the problem, it should take a few days. I am not sure what the problem is.
I still need a crowbar circuit at the input or something similar to protect the circuit from over voltage at the input. Running four buck converter may not be the best solution but it is working and a micro can be interfaced for control. All the circuits are running cool.
The stock F&P may not be the best choice for a PMA. I am rebuild another PMA so I can test the circuit with a PMA that has a lower voltage with higher current output. On the upside I did not burn up the circuit, it is still working. The project goal is 15 amp. I am about halve way there. Being able to make single sided PCB is cool, I just need to improve the circuit that is on it. :)
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http://www.jameco.com/Jameco/Products/ProdDS/387268.pdf
Hi, I was checking the data sheet for the inductor I am using and I not sure what I am looking at. There is a column for inductance value @ current. Is this the value that should be used to calculate the switching frequency for the buck converter? Comments welcome
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Hi, adding fourth stator. This will allow a 8 coil per phase configuration. I am hoping this will lower the voltage and increase the current when used with the buck converters. But I am not sure. I still have to attach the end cap.
I am planning to add a micro to the buck converter. Before I can do that the circuit needs a voltage limiter at the input. The max rating for the mosfet is 500 volts. I am searching for a circuit that will trigger at 400 volts. Any help will be greatly appreciated.
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I am searching for a circuit that will trigger at 400 volts. Any help will be greatly appreciated.
Find any circuit that will trigger precicely at a known voltage you can work with that's less than 400V, and make a simple voltage divider. Eg, if you can find something that triggers sharply and reliably at 240V, then a simple divider of 180K at the "top", 270K at the "bottom" will give you exactly 240V at the tap with 400V at the top, but you would need half-watt resistors
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I am searching for a circuit that will trigger at 400 volts. Any help will be greatly appreciated.
Find any circuit that will trigger precicely at a known voltage you can work with that's less than 400V, and make a simple voltage divider. Eg, if you can find something that triggers sharply and reliably at 240V, then a simple divider of 180K at the "top", 270K at the "bottom" will give you exactly 240V at the tap with 400V at the top, but you would need half-watt resistors
Ross;
That is just the ticket and deceptively simple. My first thought was a zener type circuit like on the analog input of the PLC boards we are messing with.
Tom
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Ross;
That is just the ticket and deceptively simple. My first thought was a zener type circuit like on the analog input of the PLC boards we are messing with.
Crossed my mind too, Tom - but then I was concerned that the original poster may have been wanting it in an AC application. The Resistor divider works fine for AC or DC. Capacitors are possibly better for AC because they won't dissipate any power, but they're not much good at DC :)
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Hi, I found a crow bar circuit that may work for the voltage limiting at the input of the buck converter. ZD1 will be replace and a load can added between the Q1 and ground. When Q1 is triggered the load may act as brake for the turbine and reset the circuit. Comments welcome ???
http://www.wiringdiagrams21.com/2009/11/28/a-typical-crowbar-circuit-diagram
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http://www.wiringdiagrams21.com/2009/11/28/a-typical-crowbar-circuit-diagram
Hi, I plan to alter the circuit to include two 200 volt zener diodes in series to replace ZD1. I am not sure if the zeners will brake down at 400 volts.
I also found a link where a high voltage laser circuit used a opto-coupler to trigger the SCR when the zener diode brake down occurred.
The strategy at this time is to use a load between the output of Q1, that will act as brake for the turbine when the SCR is trigged and include a opto-coupler circuit to provide the trigger signal. Then the circuit will reset when the turbine will slow down.
There maybe better solutions. I have orders some parts for experimentation.
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http://www.wiringdiagrams21.com/2009/11/28/a-typical-crowbar-circuit-diagram
Hi, I plan to alter the circuit to include two 200 volt zener diodes in series to replace ZD1. I am not sure if the zeners will brake down at 400 volts.
This circuit is indeed simple and generally fairly reliable. However a couple of things I'd just like to point out.
Zener diodes don't have a particularly sharp knee, so as long as you're not too concerned about the exact voltage it triggers at, you're fine.
The other thing I'd be slightly concerned about is that if your diodes break down (and putting 400V DC into a circuit like that is a fairly taxing environment), then you have the potential for a LOT of magic smoke.
A few things, in no particular order. The SCR doesn't need much gate current to trigger, so I'd put a fairly high value resistor in series with the zeners, on the "hot" side as a safety device. The 1K resistor will (obviously) need some careful calculation. Remember to calculate things like: how much current will flow if you get (say) 450V, if the zeners will survive it and how much power that resistor will need to dissipate.
If you want are more precise control of your voltage, rather than the crude-but-effective zener triggered crowbar, consider using an opamp or comparator. With a suitable divider (eg, 470K top, 6K8 on the bottom) 400V DC in would give you 5.7V on the tap. Thats easily in a safe and comfortable range for a simple comparator (eg, LM311). With its gain, you will have quite accurate and repeatable trigger points, and a nice sharp turn-on to drive your optocoupler.
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Hi, I found a solution that will work on the AC side of the bridge rectifiers and reset after it triggers.
http://www.vawts.net/t45566226/us-vawt-limiter/
I not familiar with Triac’s or Diac’s. I will have to do some reading, now that I know what I am looking for. Comments welcome
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Hi, I order the parts before I understood Steve’s circuit. I do not know if the Zeners will breakdown at 400 volts. The trigger signal is from the DC side at the buck converter input. L1 is from the AC side; single phase; from the PMA. If the SCR fires it will reset when L1 returns zero. Load could be a heating element so the PMA stator would stay cool. May be a possible solution for the input over voltage protection circuit. Comments welcome
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The trigger signal is from the DC side at the buck converter input. L1 is from the AC side; single phase; from the PMA.
The diagram, as you have it, seems certain to cause you grief.
IF you get the SCR to fire, it will do so only on every half cycle. That'll only pull down the volts on that half cycle, the other half will continue to deliver full volts.
The trigger circuit, as you have it, is unikely to work if your PMA is as I understand it. If L1 is either end of the same single phase coil, your SCR current will also have to travel through the lower diode in the rectifier, etc.
From what I've seen of your project, I'd be advising the use of triac rather than scr, and a simple opto-coupled trigger from the (now isolated) DC circuit.
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Hi, thank you for the very sound advice. I did find a PDF that shows the method. I will have to order the parts and I post the results when available. Thank again.
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concept drawing for test OVP circuit
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concept drawing for test OVP circuit
Aka, "Magic smoke" circuit :)
Recognise that it's a "concept", but:
* you can't trigger two SCRs back-to-back like that with the circuit as shown.
* Your opto is going to be FAR too soft to trigger cleanly with the 2x200V zener arrangement
* I still don't "get" what "L1" is where the load connects. How do you plan balancing the load across 3 phases?
* your comment "heat will be dissipated in the load, not the stator" is wrong. If you are dissipating any power, and your stator has any resistance, then you will be dissipating power in the stator. OK, you may dissipate less this way than say, a dead short... :)
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concept drawing for test OVP circuit
Hi
My thoughts on this OVP .
As the transfer of AC involves losses due to the high frequency in the multipole generators we tend to use. I always have the rectifiers at the generator and bring DC down.
Therefore I would be looking for a clamping circuit on the DC. SCr's can still be used but as they latch on a second SCR is required reduce the current below holding value. Its been a long time since I have worked with SCR's but I remember the second leg charged a capacitor and when the turn off SCR is pulsed it attempts reverse bias the main SCR. I will look in old texts etc. Or a mosfet or bipolar transistor could be used.
Many thanks for the info you are producing on these buck converters. I have been playing with MPPT & HV for a few years now but cheated by using a 150 v commercial solar unit Tristar .
Herb
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concept drawing for test OVP circuit
Hi Found cct At http://www.cavehill.uwi.edu/fpas/cmp/online/el10c/gibbs/Thyristors_files/image013.jpg
In normal operation the SCR is subjected to forward voltages which are below its breakover voltage and the SCR is made to turn on by the application of a suitable gate current. This gate current is usually made high enough to insure that the SCR is switched to the on state at the proper time. Furthermore, the gate current is usually applied for just an instant in the form of a current pulse. A constant gate current is not required to trigger the SCR and would only cause more power to be dissipated within the device. Once the SCR turns on, it can be turned off only by reducing its forward current below its respective holding current value.
The SCR is primarily used to control the application of dc or ac power to various types of loads. It can be used as a switch to open or close a circuit or it can be used to vary the amount of power applied to a load. A very low current gate signal can control a very large load current. The SCR in Figure 3 is basically used as a switch to apply dc power to the load resistor (R2) but in this basic circuit there is no effective means of turning off the SCR and removing power from the load. However this problem could be easily solved by simply connecting a switch across the SCR. This switch could be momentarily closed to short out the SCR and reduce its anode-to-cathode voltage to zero. This would reduce the SCR's
forward current below the holding value and cause it to turn off.
A more practical SCR circuit is shown in Figure 6. With this circuit, mechanical switches have been completely eliminated. In this circuit SCR1 is used to control the dc power applied to load resistor RL and SCR2 along with a capacitor (C) and a resistor (R1 are used to turn off the circuit. When a momentary gate current flows through SCR1, this SCR turns on and allows a dc voltage to be applied to RL .
http://www.cavehill.uwi.edu/fpas/cmp/online/el10c/gibbs/Thyristors_files/image013.jpg
Figure 6
This effectively grounds the left hand side of capacitor C and allows it to charge through resistor R1. This, in turn, causes the right hand plate of C to become positive with respect to the left hand plate. When a momentary gate current pulse is applied to SCR2, this SCR turns on and the right hand plate of the capacitor C is grounded thus placing this capacitor across SCR1. The voltage across capacitor C now causes SCR1 to be reverse- biased. This reverse voltage causes the forward current through SCR1 to drop below its holding value thus causing this SCR to turn off and remove power from RL. Therefore a momentary gate current through SCR1 will turn on the circuit and a momentary gate current through SCR2 will turn off the circuit.
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Hi, thanks for the information. Is this a complete circuit schematic?
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Hi, thanks for the information. Is this a complete circuit schematic?
No not complete just showing SCR control. combine with cct shown on backshed by warpspeed .
If you have problems I will spend some time and find out how to post a drawing.
Herb
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Hi, yes I am having problems. I save my drawing as a .jpeg file, then use the upload photo or image option that is offered at the forum. Any additional help will be greatly appreciated.
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I save my drawing as a .jpeg file, then use the upload photo
jpeg is a lossy compression standard. It is poorly suited to saving line diagrams. You will get crisper lines and smaller images if you use gif.
That doesn't alter the uploading part however.
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I save my drawing as a .jpeg file, then use the upload photo
jpeg is a lossy compression standard. It is poorly suited to saving line diagrams. You will get crisper lines and smaller images if you use gif.
That doesn't alter the uploading part however.
Trying to upload
Herb
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Wow, been a little while since I've been able to get on and look at this. Coming along rather nicely from what I can tell. I'm going to have to go back a bit and find the exact point where I last kept myself in the loop.
Seems like every time I peek at this thread there is another alternator stacked on the assembly, maybe 2. :)
The rest of us aren't going to need to do anything about the "energy crisis" if this keeps up... Between you with the turbine, and Oz with the mega PV array, you guys will eventually be generating enough juice to enable the shutting down of every other power plant world wide. I just hope you guys got some REALLY long extension cords. ;D
Keep up the good work man, it's a pleasure to watch this progress. ;)
Steve
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Hi, I have established OVP concept drawing. The thyristors may be able to be replaced with Triacs, I am not sure. Opto-isolaters will be used to separate the DC from the AC. The book I am using as a reference is for motor control. This is a first attempt. Comments are welcome.
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This is a first attempt. Comments are welcome.
OK. Constructive criticism, hope it's taken as such.
1. I doubt you can connect the gates together directly, across phases, in the way you indicate.
Its possible of course this is intended as a "functional diagram" only, and you will in fact have three, isolated trigger circuits.
2. Connecting the 3 triac/scr groups like that, with resistors to a common point, I think will come back to haunt you.
Since you must have two (minimum) devices ON in order to conduct, I've doubts that you can actually trigger them while there's no potential across them. It would seem (to me) to be a far better arrangement to connect your loads in delta directly across the 3 phases (ie, one resistor/triac from A-B, another from B-C, and the last from C-A - that way, each will be directly between a phase.
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Greetings, I have found a possible solution for the over voltage protection circuit. The circuit located at number 4 uses the AC to trigger the circuit. I could duplicate the circuit 3 times, one for each phase. When the SCR’s are triggered the added resistive load would brake the turbine to lower the input AC voltage and the buck converter would continue to lower the voltage at the input capacitor of the buck converter on the DC side. I am not sure of the values required. D5 could be two 200 volt zeners in series for a 400 volt trigger. Comments welcome.
http://www.circuitstoday.com/scr-applications
(http://www.circuitstoday.com/wp-content/uploads/2009/09/Over-Voltage-Circuit-Protection.jpg)
It looks like the circuit reset its self.
Thanks for input, it is very helpful
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Hi, If I can get the circuit working for single phase AC, this maybe a possible solution for a 3 phase configuration. Comments welcome.
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Hi, I tried to test the modified F&P with the OVP circuit. Because I modified the F&P stator I could not charge a capacitor to 400 volts to test to see if the OVP would trigger. I do have my moments. RPM was about 600 and max voltage at the capacitor was about 350 volts with no load.
Even if I add a 1:7 belt drive to the modified F&P I should be safe to road test with the buck converters.
I removed one of zener diodes from the OVP test causing the trigger voltage to be 200 volts. The OVP circuit triggered at about 200 volts and as I increased the RPM’s the voltage at the capacitor remained at 210 volts. The load resistor was only rated at 1 watt and became very hot but the circuit still functions. I have to increase the wattage rating of the load resistor.
It looks like the circuit will work for my application, if used with a wind turbine and the buck converters, the turbine will brake because a resistive load is added when the OVP is triggered and the input voltage at the input of the buck converters will remain at a save value at higher RPM’s.
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http://www.wisc-online.com/objects/ViewObject.aspx?ID=SSE5804
Hi, I found a tutorial explaining how the Zeners work in the OVP circuit. It really helped clear up my confusion.
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Hi, this is the style blade I can fabricate. The C shape will have end caps.
The big question is what style will have better performance at average wind speeds? Please cast your vote, A, B, or C.
It is a election year. 8)
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Hi, making progress. Yes you guessed correct, no wind. 3 more blade to go.
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still waiting for wind
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Hows this thing coming along? Ain't heard anything about it in a while... Either means you bailed on it (somehow I don't think so, and would certainly hope not!), or you're working feverishly to deliver the last 10% of the project in a victorious manner :)
Steve
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Hi, I am still working on it. I had minor eye surgery and I am taking sometime to recover. I was allowed to order a V3 MPPT data logger from Steve Hansel @ windgen.org. It will allow me to track changes that I make to project and I can use it to compare the results of my circuit to determine if I am heading in the right direction. I am fabricating a RPM sensor and anemometer, just a basic reed switch and magnet configuration. I redesigned my belt drive transmission to reduce fabrication cost. I had to complete a insulation project on my house before the snow arrives. I attended a Tektronix seminar, great presentation on there new spectrum analyzer. If anyone has a chance to attend, I highly recommend it.
It is a very busy time of year. No pictures at this time but I should have a lot to report in the next few weeks. Thanks for the interest, enjoy the holidays.
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http://files.activeboard.com/1193689?AWSAccessKeyId=1XXJBWHKN0QBQS6TGPG2&Expires=1351123200&Signature=DMa4NPoMMIh2komJvHxxupLg0r8%3D (http://files.activeboard.com/1193689?AWSAccessKeyId=1XXJBWHKN0QBQS6TGPG2&Expires=1351123200&Signature=DMa4NPoMMIh2komJvHxxupLg0r8%3D)
Hi, manual for V3 MPPT controller and data logger.
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Hi, completely assembled F&P with belt drive. I counted the ratio and it is 1:4, I made a mistake earlier . I am going to tighten the belts and run it with the drill press for a few hours. Manually spinning the center shaft ;which is direct drive; VOC about 80 volts @ about 40 RPM.
I ordered a intronics solar MPPT25, it has a battery charging algorithm. The only problem is the max input voltage is 80 VDC. I will have to add a OVP circuit that will trigger just under 80 volts and configure the F&P as four 3phase with 3 coils per phase connected in parallel. I was communicating with one their engineers and he said it should not be a problem as long as the OVP triggers. I plan to continue working on my circuit.
http://www.intronics.com/products/pdf/MPPT25.pdf
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Glad to see your eye is healing well... As I'm sure you are as well. That's a pretty machine there. ;)
I've lost track a bit... What kind of power are you looking to get in the final product? I've seen the numbers jump around a bit, as well as the configuration of the genny as it evolves, so I'm curious where it stands.
Steve
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Hi, the project goal is 15 amps at 12 volts. I am using a F&P axial flux. The stock modal is configured as a 3phase star with 12 coils per phase. The reason I switched to the F&P is because they are low cost, light weight, and it saves on fabrication man hours. The biggest problem with the F&P is high internal resistance of the stator.
The backshad forum has information on how to modify the stator to form multiple parallel 3phase configurations that lowers the internal resistance value. I am using small circuit board to make the alterations of the connections of the coils. There is no cogging but there is drag.
I verified the benefit of adding a MPPT with my circuit. I purchased a commercial MPPT controller that has a 25 amp limit. It was the only one I could find with a high input voltage that is within my price range. I will have to configure the F&P stator the form four 3 phase stars with 3 coils per phase connected in parallel.
I have to configure the OVP circuit trigger at 75 volts to protect the MPPT.
The VAWT is slow. I added the belt drive transmission with a 1:4 ratio. The blades on the VAWT are 6.5 feet with a J shape. I can adjust the blades size and position, the belt drive ratio, and the stator configuration for the best performance at low wind speeds when using a MPPT.
Hopefully the system well be installed before it snows so I can test it over the winter.
The weak areas of the project are the input voltage limit of the MPPT25 and the belt drive transmission.
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Hi, completed belt drive for F&P PMA. It would be nice to find a supplier for the pulleys. The pulleys are DIY V wall. The belt drive ratio is 1 to 4.25
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Looking nice!
Decided on a color change?
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Hi, the red pulleys are cogged and the intent was they would function like a timing belt but they were not working well. I had cut new pulleys with no teeth and the red material was out of stock. I installed smaller springs to reduce the load on the belts and it spins much easier. I have to install a RPM sensor and then I can install it outside on the mast.
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Hi, project update. The belt drive I fabricated is poor quality, the belts are slipping. Because the belt drive is the problem I am configuring a direct drive dual F&P PMA. Plot shows manual operation of PMA in fixed duty cycle mode at 30,40,50, and 60%. I hope to have it outside on a mast in a few days.
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I can't remember if it came up in this thread or not... But have you considered a chain drive instead of belts? Yes, they will be noisier, but they won't slip and certainly will have much less friction losses...
Just throwing it out there.
Steve
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Hi, thanks for the suggestion. I have decided to go with auto timing belts. This works well and I have resolved all the fabrication problem. Large pulley 54 teeth, small pulley 34 teeth. The timing belt drive will be same configuration as the V belt drive without the slipping problem. I am fabricating new blades and I should have the new VAWT operational in a few days. The new strategy is to use multi small VAWT connected in parallel. The cost will be low cost , they are easy to fabricate, and I will have a higher output at low wind speeds. Thanks again and I will post results when available.
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Once again, nice looking work.
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Hi, I installed new version of 5 blade VAWT. Cold….. waiting for wind.
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Awwwww yeeeah.... That's what's up...
But don't stare at it waiting for the wind. The rule is 3 days. Word has to spread from air molecule to air molecule untilit reaches the wind gods. Or so I'm told ::) ;D
Nice build man, hope it performs just like it looks... Keep us posted ;)
Steve
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Sweet, as always watching intently.
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Hi, sadly the RPMs are very low…. I had 10 to 15 MPH wind speed and the PMA never reached the speed that I had achieved with manual operation. I am making modifications to the blades and I am starting to fabricate a axial flux PMA that should have a higher output at lower RPMs. At the highest wind speed the max current output was 0.07 amps, sad but true. :'( It should take a few days to complete the modifications. :)
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The leaning tower of VAWT. The winds were strong enough to bend the mast shaft. The mast blade rotor bearing saved the day. I think it would have been catastrophic without it. I am making repairs and doing modifications.
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Hi, I was able to do a few quick modifications. I mounted the 6 blade J rotors to the stock F&P with the 1 to 2.5 timing belt drive. It start charging the battery at about 3 to 5 MPH wind speed. I have to install the RPM sensor and calibrate the software. Weather forecast predicts windy conditions for the next few days. Will post results when available. After struggling with the installation, multiple small VAWTs are looking very appealing.
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Hi, I am getting about 1 amp @ 8 MPH wind speed . The stock F&P needs a faster blade design, I think it is better suited for a HAWT or micro hydro mill.
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Keep at it man... This thing has come a long way... ;)
Steve
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Hi, if they are rated at 28 MPH windspeed, then it is 500 watt VAWT. The problem is I do not get a 28 MPH wind that often. Without the MPPT the output would be nothing. I still have a few more modifications to make to the blades. After that I can make some more. They are low cost and easy to fabricate, I can start a nano wind farm. ???
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Hi, 2.4 amps output at about 11 MPH. The timing belt is jumping the cogs. I can hear it from inside the house. It is a easy fix, I just have to tighten the pulley shaft so it does not move. The springs are allowing the shaft to move. The belts should not stretch.
I suspect the output will increase when I fix the belt jumping cog problem.
peak recorded wind speed 13 MPH.
(http://www.vawts.net/download.spark?ID=1251417&aBID=125317)
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Today’s project, fix the deck. VAWT crash….
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Yeah, the power of the wind is astounding in what it can tear apart given the chance. Maybe it could have survived if it had been attached to the floor joist rather than the boards?
At least nobody was on the deck when it went wobbly.
I suspect it will rise again?
Tom
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Hi, project update. Because of the cold weather and the damage to the VAWT I am spending the rest of winter working on my test circuit. VAWT testing will continue in the spring.
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Yeah, the power of the wind is astounding in what it can tear apart given the chance. Maybe it could have survived if it had been attached to the floor joist rather than the boards?
At least nobody was on the deck when it went wobbly.
I suspect it will rise again?
Tom
Hi, very true. I learned a lot from the experience. The VAWT received damage to one blade and 4 blade rotor hinges. The center of gravity is to high. What is interesting is I was able manually operate the PMA with a hand crank and achieve a 5 amp output @ 12 volts. The highest record wind speed was 19 MPH and the output was about 3 amps. The blades are slow and the timing belt was jumping the cogs on the pulley. Three problems will have to solved.
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Oh man... That's up close and personal there...
There are many things I have come to find are very easy to underestimate... And while I've never had the pleasure of finding out personally with a wind turbine, I've seen enough pictures to know that nothing its immune... They all have a weak spot, and it almost always involves direct physical damage to the turbine or tower, or both, which you have certainly found out. :(
Glad to see though that your spirits aren't dampened by this - learning hard lessons is a very significant part of the "fun" with this stuff. It will rise again... :)
Steve
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That is terrible news. But, you've overcome worse, and will again I'm sure.
Just because misery loves company, attached a pic of what a "not quite tight enough" clamp
can cause in a big wind.
Happened a couple of years ago.
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Ouch.
Pain in my guts just seeing the photos.
Sorry to see it,
G-
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Wow, sorry to see it cut short, we were all just starting to have fun seeing it start to do something.
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Hi, before the crash I had no notion of the forces acting on the turbine mast. The data obtained revealed the PMA RPMs have to be doubled. The belt drive ratio will have to be increased, the blades will have to be modified to reduce drag, and the mast foundation will have to be a lot stronger. Waiting for warmer weather so testing can continue .
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Hi, I had some free time so I fixed the VAWT, strengthen the foundation, removed the springs from the belt drive to prevent the belt from jumping, and it is operational again. To cold to take to take pictures. After reviewing the test results, I am increasing the belt drive ratio a small amount. That should make the output about right for this size VAWT. Waiting for wind…..
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Hi, before the crash I had no notion of the forces acting on the turbine mast. The data obtained revealed the PMA RPMs have to be doubled. The belt drive ratio will have to be increased, the blades will have to be modified to reduce drag, and the mast foundation will have to be a lot stronger. Waiting for warmer weather so testing can continue .
THAT is why I am pro HAWT.
VAWTs look cheaper and easier, until you try to build one.
I do admire your tenacity...
Both with finishing a project and getting that thing flying again in this weather!
G-
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Hi, the hard part for me was designing and finding the materials to allow me to fabricate a low cost VAWT. For this size VAWT I should be getting 4 to 5 amps @ 12 volts output at about 10 mph wind speed. I still have a few problems to solve, but it can be done. Have you seen the Caltech study? It all depends on how you look at the numbers. I find this style VAWT easy to fabricate and my plan is make more then one and connect them in parallel. I live in a low wind area. The stack F&P may not be the best choice, but using a MPPT type circuit really helps the output. I now have the knowledge to fabricate a axial flux if it is required. Most of the cost for the project will go towards the mast. ;D
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Hoping to remove load added by transmission
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No wind, no power. The Pgen is just for testing the circuit and maybe burn a few calories. :)
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Hi, after waiting the last 10 months for wind, the large blue VAWT revealed a problem with the plastic composit large blade rotor. The material sagged and the weight of the large blades pushed the belt drive pulley out of alignment. I will have to add lower rotor supports or upgrade the material that is being used to aluminum or steel.
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From the pics, that sagged quite a bit. A setback, but one I'm sure you can handle.
Good luck
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Hi, the truth about the project is I really live in a low wind speed area. Fabricating a large VAWT is to expensive for the amount energy I can harvest. The high wind speed only happens a few times year for really short periods of time. Basically I taking the PMA and buck converter circuit and applying to a small steam engine project. I learned a lot about power generation from the VAWT that I never would've realized if I had started with a different project.