Anotherpower.com Forum
Renewable Energy Questions/Discussion => Renewable Energy Q&A => Topic started by: artv on January 08, 2012, 06:48:39 pm
-
Hi All,
I've been testing a modified car alt I received from a very generous member from this and the "other" board.
It was wired star ,with a built -in rectifier, it had one lead out +,..I assume the shell is -,
Took it apart, found the star point ,now it's wired IRP
Anyone of the single phase's (by itself) put out ,..21.4Voc, ..connect 4 lights,..7.3Vdc,...9.3amps=68w
When I series' the 3 outputs ,...62Voc,...lights,..8.3Vdc,...10.43amps=86.6w
Why don't the phases add up ???
I've tried everything under the sun, but they just don't add up??
Shouldn't it be,...3x68=204,...minus doide and resistive losses??
Each phase puts out 68watts (with 4 lights)....
Does this have to do with "matching the load"???
Be careful what you ask for ;)...........Thanks.......artv
-
I replied to your (almost identical) post on the other forum.
-
I don't know if you got any responses on the other board except Ross pointed out here that he responded, I haven't read it there yet. But if I know him at all, I am sure Ross pointed out that since it's 3 phase the phases wont just add up. When one phase is fully charged in one polarity the others are not going to be at that same relative point. You could play with capacitors, but they wont work with anything big without making it more costly than its worth.
-
The #'s above have nothing to do with caps.
IRP, each phase has it's own bridge, then you wire the bridges in series, for the overall output.
Is that not how it's done?
68 watts out of any (one) of those outputs, series them up and I only get 86.6 watts??
Seems the space would be better utilized just making single phase??
I know I'm wrong but why?.....artv
-
The #'s above have nothing to do with caps.
IRP, each phase has it's own bridge, then you wire the bridges in series, for the overall output.
Is that not how it's done?
Short answer? No, that's NOT how it's done.
You NEED to understand AC theory here as well as the simple arithmetic sum of voltages in simple DC circuits.
If you draw the 3 phases IN THEIR CORRECT RELATIVE PHASE, then draw what they look like once they've gone through a bridge rectifier, again IN THEIR CORRECT RELATIVE PHASE, and *THEN* sum them, you might see the answer.
"I can explain it to you, but I can't understand it for you"
-
Here is a good website with a primer on single and poly phase motors
It may *help* you understand enough that a bit of googling could fill in the gaps
http://www.coilgun.info/northrup/theory.htm (http://www.coilgun.info/northrup/theory.htm)
I can use it to give you a basic idea, though not a complete explanation
If I am wrong, anyone, please step in and correct me
Here is representation of a single phase AC
(http://www.coilgun.info/northrup/images/p306_fig2_3.jpg)
This has a single rise and fall of potential, As illustrated a cycle is measured from one peak to the next.
If you had another alternator which is locked to match the rise and fall of this phase, you could increase your voltage through placing them in series.
Here is a 3 phase AC representation
(http://www.coilgun.info/northrup/images/p308_fig4_5.jpg)
This shows how each phase separated by its position relative to its rise/fall of between max+ 0 and max-
It should be easy to see by this image, that while phase(a) at its max+ none of the others are.
In fact phase(c) is on its way the opposite direction, but not at the same degree as phase(a).
They are 240 degrees separated.
I am not an expert at this, so keep that in mind.
I hope this helps give you an idea why it does not simply "add up"
-
OK, I don't usually do this... but to make the point, I just quickly mocked it up for you.
Here's a graph showing ideal 3-phase. Voltage (vertical scale) against time (horizontal). Each phase is 120 degrees apart.
[attachimg=1]
Here's what each phase looks like once you full-wave rectify them.
[attachimg=2]
And if you were to simply add them in series you get this
[attachimg=3]
The volts scale is relative, so if you have a 30v input, "1" = 30V. "2" = 60V etc.
Does that make it any clearer?
-
Wolv & Ross,
Thank-you for taking the time,...but I'm pretty sure I have a handle on 3 phase ..
I'm using IRP ,when you put the 3 individual rectifiers in series, the output voltages add..
But being 3 phase ,only one of those phases is at max output,..one is climbing towards full output, while the other is declining from full output...
Wouldn't it be better to have all the coils at max out all the time (single phase) as opposed to one third of the time....I know this would result in sort of a pulsed situation (bad vibration)...
When the 3 phases are putting out 68watts each, you should be able make use of it , instead of only 86watts........doesn't make sense to me.........artv
-
Wolv & Ross,
Thank-you for taking the time,...but I'm pretty sure I have a handle on 3 phase ..
I'm using IRP ,when you put the 3 individual rectifiers in series, the output voltages add..
But being 3 phase ,only one of those phases is at max output,..one is climbing towards full output, while the other is declining from full output...
That's a pretty 2-dimensional view of it, but in the context, yes.
Wouldn't it be better to have all the coils at max out all the time (single phase) as opposed to one third of the time....I know this would result in sort of a pulsed situation (bad vibration)...
You know the problems people complain about with turbines not "getting away" at low wind speeds? If all phases were in-phase, it'd be an unimaginably difficult thing to handle. 3phase applies virtually constant torque (load). Single phase is very "lumpy"
When the 3 phases are putting out 68watts each, you should be able make use of it , instead of only 86watts........doesn't make sense to me.........artv
You certainly CAN make use of it. It's just that you're trying to use it the wrong way.
Sure, a shifting spanner CAN be used as a hammer. It rattles some, and it doesn't hit square, and it's hard to hold. Should they re-design it so it works better as a hammer? Or should you use a hammer (the right tool for the job)??
-
I think this is a matter of not fully understanding your needs artv
as 3 phase is superior if matched to your load and needs. it DOES have the capacity to deliver exactly the same power, if matched the same as a single phase.
The more phases the smother the genny will load the blades, and the lesser the ripple to the rest of your RE system as the phases will cut the time that in between the total output drop/reversal
on one hand a single phase unit is technically "stackable" but such a setup has many other drawbacks, and essentially self defeating in nature to rewire a polyphase to a single.
However, what we are pointing out is you just cannot *stack* 3 phases to make up for that mismatch.
You can see if you can change your wiring config inside from Delta to Star to see if you can obtain a better match.
I do not know where you are with this, or the details of your alternator. If you can supply more information , where yo are, what you have tried, and maybe some images I think I, or anyone else with experience could better help you.
We are currently having to make assumptions how your setup, this leads to misunderstandings, and maybe not the best answers. It can be frustrating to everyone.
Quoting a friend, this is all part science, part black art.
I'll do my best to help where I can
-
Hi Guys,.. I really appreciate the replies, I should state that, I am just trying to get the most out of the generator .....I figure the more I can get out the more I can use..I'm thinking of building a big tower, with big blades,something that won't even see one of these generators as a load...
have an engage an disengage to the genny's when needed........
The genny's will be on the ground in a shop , the only thing in the air will be the blades and the differential gears .........It might be a wild dream , but the tower is going up this spring.....
I'll definately need help with the blades...........
Just want to build the best generator first ,before I go to all the work involved with tower construction......I can build just about anything under the sun .....but all this electrical stuff has me confused........ok you can laugh now .....but time will tell......Art V
-
but all this electrical stuff has me confused........ok you can laugh now .....but time will tell......Art V
There is nobody on this planet that was born knowing this stuff.
Period.
-
Sounds like you have a lot of fun work ahead.
We will help as much as we can but the more information on what you got,
within reason of course we don't want to know if you farted building it or anything.
But general the better we can help you then
-
I'm using IRP ,when you put the 3 individual rectifiers in series, the output voltages add..
I think is one of the problems - you don't put the bridges in series with IRP. The DC side is hooked in parallel. IRP delivers the voltage of one phase, with three times the current of one phase. It's kind of like a delta connection without the delta connection.
On the single phase issue I have found, despite the loading characteristics and relative "inefficiency" of single phase vs three, that in the real world it does work OK on a wind turbine. The reason it works is because most three-phase gens are too "stiff" and won't let the blades spin at optimum Tip Speed Ratio once a load gets applied to the gen. Single phase is less "stiff" because it only loads the input shaft when the voltage of the sine wave is high enough for the diode to conduct.
When it comes to getting power out of a wind turbine, having the rotor running at optimum TSR delivers the most power it can make to the input shaft. That is usually way more important (with higher power yield) than how many phases the generator has.
With the single phase experiments I have done with geared generators, they worked fine and ran fairly smooth with no noticeable vibration. At slower speeds and frequencies, however, single phase can be a bear because it will make your turbine and tower rumble pretty good due to the cyclic loading of the input shaft.
--
Chris
-
but all this electrical stuff has me confused........ok you can laugh now .....but time will tell......Art V
There is nobody on this planet that was born knowing this stuff.
Period.
I was born knowing EVERYTHING, but I forgot almost all of it before I learned to talk. :o
-
Baby Geniuses ;D
-
Anyone of the single phase's (by itself) put out ,..21.4Voc, ..connect 4 lights,..7.3Vdc,...9.3amps=68w
Does anyone else think the 14 Volt drop, from the Open Voltage of 21 Volt) down to the Loaded Voltage of 7 Volts, is excessive? Is 9 Amps optimal if the Voltage drops that much?
-
erm ...i think the given load will always clamp the voltage ....so the load will always win ...ish ..i think
but its interesting to think about single phase ....i like single phase ...lumpy ..yes ..and it will shake things about a bit , ....but all things considered ...why not ?
3 phase seems to lock you into two set v points....star/delta....with single phase there can be a lot more ....a 12v stator could possibly be run at /24/48 ...even 96v...(depending on the number of coils)
as long as the prop is happy ..?
-
erm ...i think the given load will always clamp the voltage ....so the load will always win ...ish ..i think
Please explain how the load of "4 lights" used by ARTV, "will always clamp the voltage".
I am not following your logic.
....so the load will always win ...ish ..i think
HUH?
-
mmm...yes its not the best logic
the open circuit voltage will be high ....the bulbs each add low r into the circuit ...the more bulbs in parallel the lower the resistance ....the alt at a given rpm can only produce a certain amount of amps ...not enough for those bulbs so the voltage falls back ...increase the amps and it will rise back up....
go the other extreme and put 20 bulbs on it ....now the v will be very low ...its all being lost as heat into the load .....( thats a little vague but i think? its ok to say that )
its all down to ohms law ....but i,m hopeless at that
another shot is ...the amount of resistance added by Artv to the open v will directly effect it ?
maybe someone else can chime in on ohms law .....
-
its all down to ohms law ....but i,m hopeless at that
Well yes kind of, but actually, my original point was the huge difference between the Open Circuit Voltage of 21v and the Loaded Voltage of 7v at 9 amps. Therefore, the generator is wasting about 126 watts in heat to deliver 63 watts to the load. Is that an optimal load for that generator ?
-
my original point was the huge difference between the Open Circuit Voltage of 21v and the Loaded Voltage of 7v at 9 amps. Therefore, the generator is wasting about 126 watts in heat to deliver 63 watts to the load. Is that an optimal load for that generator ?
The open circuit voltage dropping to only 7V under load in no way "means" that there is 126 watts "wasted in heat" to deliver such a modest power to the load.
Many devices can (and do) generate very high open circuit voltages. A current transformer for example, may produce hundreds or thousands of volts if unloaded - but that doesn't mean they're "wasting" hundreds or thousands of watts just because once loaded their voltage is millivolts to volts.
-
Some times it pays to stand back and look at what we are measuring.
The 21v open circuit has NO wattage associated with it, as Watts = volts x current.... or 21 x 0 = 0watts.
So we havent wasted anything yet.
When we load it with a load, the current flows in the load and the stator equally... so whatever voltage is forcing the current through the combined resistance of the stator and load , will dictate the output current
ie if 5 amps flows in the load, it must be flowing in the stator as well, so the resistance of the circuit is the load plus the stator.
So we know to get a current flowing in the load, we need current of equal value flowing in the stator.
This is not just an ohms law problem however, and that explanation will only work for alternators with no reactance or impedance from other factors.
In truth, the alternator suffers synchronous impedance, which is frequency and load sensitive, as it means we need the losses from resistance in the stator, armature reactance in the alternator, and impedance caused by the waveform through the inductance of the stator.
To keep it simple we can try to use just ohms law in the stator and load.
Now this may work well for air core alternators with strong flux, very low resistance stators,and large air gaps, but for any unit that relies on steel laminates, and poorer magnetic fields, and tight tolerance air gaps.......the reactances and impedances will current limit the alternator at some point, rendering the ohms law approach useless in the extreme.
At current limit (from reactance etc) it will yield ever higher open circuit voltage as the rpms rise, but the loaded voltage and current will remain the same from that point on.................. we are still wasting the heat in the stator at this point from stator resistance and current flow, but are NOT using any more motive force after current limit occurs.
So if were lucky, and this point is arrived before the destructive heat loses occur, we have a bullet proof alternator heat wise, but we won't be able to stop the prop by shorting it out either...
Does that now explain where the power didn't go?.... it wasn't there in the first place when open circuit...... or short circuit for that matter.
When short circuit, the motive power used, purely drives the loses in the armature and stator, as no voltage emerges from the alternator, so the output is also zero watts.... but maximum current (I max) .... opposite to open circuit (V max), but same power output.
The power absorbed in the alternator is now defined by the current x current x the resistance of the stator, ( I^2R) as the reactances dont behave like resistance does, there are no real loses in reactance voltage limiting, verses resistive current limiting, same for capacitive reactances and their effects on voltage dropping schemes in electrical circuits that don't want to use transformers because of weight or space requirements.
The capacitive and inductive reactances impede current, and may be expressed in ohms, but they are frequency sensitive, and don't follow ohms law.
Think of your welding transformer. The primary may measure 2 ohms or less. At 240vac 50hz input this should mean 120 amps flow through the primary..... but no, only a few amps flow (shows as magnetising current) through the winding. The AC sees the inductive properties of the core and windings, and so (until you short the secondary with your welding rod) use very small current to idle. A 2 ohm resistor is a totally different animal...I=E/R = 240/2 = 120A..... W=ExI = 240 X 120 = 28800 watts ( or use I^2R).
In simple terms, current will appear as torque, and voltage will appear as speed (rotation). A shorted alternator has heavy torque to drive it and no output voltage, and an open alternator has ( high) speed, but uses no torque (bearing and iron losses excepted) and no current output.
Under normal (whatever that is) resistive loads, it will be a combination of torque and speed that gives us power output, and an ideal alternator will have a linear power curve, but nothing is ever ideal.
....................oztules
-
my original point was the huge difference between the Open Circuit Voltage of 21v and the Loaded Voltage of 7v at 9 amps. Therefore, the generator is wasting about 126 watts in heat to deliver 63 watts to the load. Is that an optimal load for that generator ?
The open circuit voltage dropping to only 7V under load in no way "means" that there is 126 watts "wasted in heat" to deliver such a modest power to the load.
Many devices can (and do) generate very high open circuit voltages. A current transformer for example, may produce hundreds or thousands of volts if unloaded - but that doesn't mean they're "wasting" hundreds or thousands of watts just because once loaded their voltage is millivolts to volts.
I do not agree with your analogy of comparing a Wind Powered Generator to a Current Transformer. At a fixed RPM, a Wind Powered Generator is in the "Constant Voltage" class of power sources. A "Current Transformer" is not in that same class. And, as you pointed out and I agree with, a Current Transformer has a very different set of Open Circuit characteristics. Under normal conditions Current Transformers are not typically operated with an open secondary. An Apples vs. Oranges comparison, at best.
-
In truth, the alternator suffers synchronous impedance, which is frequency and load sensitive, as it means we need the losses from resistance in the stator, armature reactance in the alternator, and impedance caused by the waveform through the inductance of the stator.
Now this may work well for air core alternators with strong flux, very low resistance stators,and large air gaps, but for any unit that relies on steel laminates, and poorer magnetic fields, and tight tolerance air gaps.......the reactances and impedances will current limit the alternator at some point, rendering the ohms law approach useless in the extreme.
At current limit (from reactance etc) it will yield ever higher open circuit voltage as the rpms rise, but the loaded voltage and current will remain the same from that point on.................. we are still wasting the heat in the stator at this point from stator resistance and current flow, but are NOT using any more motive force after current limit occurs.
....................oztules
oztules,
OK, yes there is a considerable amount of iron within this car alternator being tested.
That means the Inductive Reactance of this alternator would be higher than a Dual Rotor Air Core Axial Flux generator. RIGHT?
But how much higher?
How does the Inductive Reactance compare to the DC Coil resistance for this type of car alternator?
Is it ?
a) significantly less
b) about equal
c) significantly more
Agreed, the DC Coil Resistance would cause energy to be wasted as heat
and the Inductive Reactance should not waste the energy as heat.
If there was significant Inductive Reactance (as compared to the sum of the coil resistance + load resistance) then could this be observed and measured because the AC Voltage would be "out-of-phase" with the AC Current ?
-
I'm guessing those numbers, if not randomly picked, were characteristic of that machine.
Then it's dependent on how the genny was made.
So unless I missed something in this thread..
We are not privy to wire gauge (or the metal makeup of the wire used ie copper clad aluminum, copper etc), core makeup, amount of wire involved, or even how much the load reduced the blade speed.
So answering this Anyone of the single phase's (by itself) put out ,..21.4Voc, ..connect 4 lights,..7.3Vdc,...9.3amps=68w
Does anyone else think the 14 Volt drop, from the Open Voltage of 21 Volt) down to the Loaded Voltage of 7 Volts, is excessive? Is 9 Amps optimal if the Voltage drops that much?
Becomes tricky
-
I am however interested in how Artv's machine is turning out.
Or was this posted elsewhere?
-
I am however interested in how Artv's machine is turning out.
Or was this posted elsewhere?
I am not sure how the machine turned out.
"... modified car alt ..."
I am not sure how the PMA was modified either - no details were posted ...
a) The electromagnetic rotor was pulled and replaced with a shaft containing permanent magnets.
b) The stator was re-wound for more volts at a lower RPM
c) All of the above
I would like to know the RPMs of the PMA when it generated the 7.3 volts at 9.3 amps = 68 watts.
I am going to guess between 350 rpm and 400 rpm.
Is that roughly a 5' diameter blade with 20 mph winds?
-
I do not agree with your analogy of comparing a Wind Powered Generator to a Current Transformer.
You don't have to. I made an observation of fact based on an incomplete and unspecified question.
Under normal conditions Current Transformers are not typically operated with an open secondary. An Apples vs. Oranges comparison, at best.
Under normal conditions wind turbines are not typically operated with an open output either.
-
"oztules,
OK, yes there is a considerable amount of iron within this car alternator being tested.
That means the Inductive Reactance of this alternator would be higher than a Dual Rotor Air Core Axial Flux generator. RIGHT?
But how much higher?"
Magnitudes in some cases. from uH to mH
"How does the Inductive Reactance compare to the DC Coil resistance for this type of car alternator?
Is it ?
a) significantly less
b) about equal
c) significantly more"
Ok, there is a bit here to look at.
The impedance caused by the inductance of the circuit is frequency dependant. So at low frequency, the difference between stator R and stator R+XL is insignificant.
As F increases, so too will the impedance caused buy the inductive reactance of the circuit.... thats why it is an impedance not a resistance, it is dynamic in nature.
So the answer is all of the above... depending on the frequency.
Which brings the next part of the question.
"
Agreed, the DC Coil Resistance would cause energy to be wasted as heat
and the Inductive Reactance should not waste the energy as heat.
If there was significant Inductive Reactance (as compared to the sum of the coil resistance + load resistance) then could this be observed and measured because the AC Voltage would be "out-of-phase" with the AC Current ?"
The answer is ...yes... need to measure synchronous impedance, and subtract the resistance losses, and then whats left will be mechanical losses,inductive reactance and the real elephant in the room with iron cores... armature reactance. (even though the inductive reactance acts like a choke... current limiter).
There are many how too's on how to measure the reactive components, open circuit to short circuit measurements will give you most of the answers.
Think of it like this.
If we use a magnet to induce a voltage in a wire, and load that wire, a current will flow in that wire. Simple enough too....
But, whenever we have a current flowing we create a magnetic field....so now the wire with the induced EMF is now an electromagnet whose field is in opposition to the magnetomotive force that induced it. (MMF).
We can see that now we have an inducing field and a repelling field produced by that field.... it's war. As long as the inducing field (rotor MMF) is stronger than the repelling field (Back MMF), we can continue to drive up the rpm, and get power out of the stator.
When the stator is carrying enough current to create back MMF sufficient to prevent further MMF from seeing the stator, we get a state where no matter how fast you spin the shaft, no more EMF can be induced in the stator.... we CURRENT LIMIT at this point.
If the air gaps are large (like in an axial flux with neos) and the stator coils are without iron (axial flux with neos again) and we have a strong magnetising field (neos etc) then we have a machine that will follow the ohms law pretty well, and we can ignore the armature reactance, and the inductive reactances....... but...
In a car alternator we have tight gaps for the field to operate over, and we have iron core in the stator with slots. These slotted iron cores allow much lower magnetising current to be used, and much tighter air gaps ( 1mm instead of 20mm). The stator wire is wound around these slots/poles, and that allows the flux induced by the rotor to cut the coils at one instant, as it flicks and drags from pole to pole........ in an axial, the coil pole is physically spread.....and without an iron core of any kind to focus the back MMF against the magnetising field.... and so the field penetrates the legs of the coils gradually, not all at once.
So a combination of gap (bigger is harder to focus the back MMF), and an iron core focussing the back MMF, we have a completely different animal to deal with.
As a car alternator, when these problems arise, we simply increase the flux in the magnetising field (rotor), and that papers over the problems for the most part.....
A car alternator will still current limit from armature reactance, depending on the max flux the rotor can create with full battery voltage across it ... for a car usually 5A is about it for the 14v driving emf. The rotor resistance limits it to that, and so the AMP TURNS that can create the field is limited to this value.
The inductive reaction from just the frequency in a car alt does not cause quite the results that back MMF does in most cases, as F is not usually so high as to bring it to the fore front, it will usually be just be a creeping output loss on the back of the armature reactance. In a car alt, the turns are very low, the core very small, so inductance is low.
In short, in an iron core machine, it will almost always be the back MMF of the armature reactance (and XL) that defines the upper limit, and the resistance that defines low power performance. in commercial generators, they tend to balance the copper loss with the armature reactance (and XL)losses.
It is really an excellent safety valve, as if it did not occur, then a short in a power alternator would probably destroy it, and bust shafts pronto.
Power factor losses are a vector thinggy, and so should not bother the alternator at first glance.... but it you need say 10 amps available to vectorially get 7 real amps in phase with the voltage, we still have to make the 10 amps.... Now there is no voltage associated with the last three amps so no power... so we should not require any more motor to develop it... but no... sadly.
Current exhibits as torque, so even though no power should be associated with the phantom current, the motor will feel it. Folks charging batteries with no PFC stages will notice this behaviour. The 10 amps needs to be carried to the work site, and the resistance in the wires, fuses, transmission whatever will exhibit a voltage drop, producing a voltage proportionally(albeit small), and our phantom current has a small in phase voltage now... not much in the way of watts, as V is small, but the 3 amps still exists, and torque will need to be found to support it...... motor labours accordingly. I would think that the 7 amps to 10 amps will give the ratio of change of torque in this instance...... because torque is proportional to current, as rpm is to stator voltage.
It is the stators back MMF fighting against the rotors MMF that makes the shaft hard to turn when load is applied..... it is only caused by current flow, as only current makes flux.... in ampere turns.... ideally, EMF has no effect ( does in the real world... we need to overcome internal resistance / impedance for the current to flow... but you get my point?)
.................oztules
-
Windyone,
Here is a copy of another answer regarding alternator design for windmills on another site. I'm too slack to re-write it, so I present it in full for your perusal. It may answer some more questions you may have
.... start waffle
Ok Bob,
I will approach this a bit differently.
We can measure the voltage from the power point, and the voltage meter will say 240vac... thats fairly obvious for a 240v system this country runs. (Aust)
If we look at the oscilloscope, we can see that it is not a 240v pulse at all, but instead rises from zero up to 320v and back to zero, but the meter said 240vac??
If we look at a square wave 240vac with an ac meter, it will say 240vac. The oscilloscope will see that we start at zero, rise instantly to 240v and then drop to zero instantly again at the end of the time span (note the time for each wave covers 1/100th second for both/all of this discussion.)
The meter is correct in both cases, even though one had a peak voltage of 320v, and the other was 240 peak.
It is the area under the curve that was the same in both instances, even though the peaks were different.
Doubling the diameter and so doubling the speed with the same magnets and coils that the smaller diameter one had, carries the same lesson.
The skinny high peaks of the big diameter and the smaller fatter peaks of the smaller diameter both have the same area under their respective wave form curves..
So we can say there is no difference.
Well no...
In practice there is a difference, and you may recall somewhere recently, Flux said there was a diameter that was ideal, and others that weren't.
space is one reason, overlapping flux is another , and both these should be better in the larger diameter... and they are..... but......
Think of the skinny high peak waveform, where the peak was higher the ohms law comes to kick you in the butt.... If your coil R is the same in both instances, but your peak EMF is higher, then Voltage loss in the same coil is higher.... ie I=E/R, so if E is higher, then I is higher for the same rpms with the larger stator.... worse the losses in that coil will be I^2xR...so that makes it worse still.
So now we can say that the losses in the bigger diameter machine will necessarily be higher than the lower voltage spread over a longer angular interval... because the peak currents are lower through the same resistance.... we lose.... but fun while it lasted.
If we fill in the gaps symmetrically to make twice the size machine, then thats a new machine entirely.
Now:
"*for the record
this is a theoretical discussion of what is possible, not something that i am claiming as new, better than, worse than, or even desirable or useful. as Flux has stated there really is nothing new in the generator game other than materials used. every possible configuration has been tried, proven and used by the late 1880's including the air core axial machines.
kicking the ball back to center court"
Matching the load is the goal, and we need to match the impedance of the air to the impedance of the battery. This involves a mill with blades, an alternator and a basically fixed impedance battery.
The basic mill tries to match the variable impedance of the air, to the variable impedance of the alternator to the fixed battery.
We can fiddle with blades, blade size, wire, magnets, mill diameter, resistance in the line, black boxes, star delta switching, transformer tapping, high leakage transformer coupling, direct coupling and the list goes on.
The fun thing about mills, is that it HAS to be built with an eye to everything. The moment we try to optomise any part, we alter some other parts.
Folks like Chris optimised the resistance in his alternator. He did this with higher speed, which allowed his resistance to be very very low.... but this makes it virtually unusable for direct coupling, so black box is needed to match back up all the mismatch imposed by the low resistance.... if he had zero resistance, and no black box, it would never go beyond cut in.
We can use higher resistance stators, and get good low wind performance, but the high winds burn them up... unless we can use a black box, or cool it, or star delta it perhaps... of furl early.
There are other tricks that can be used which you would have seen in your bigger alternators. An automatic star/delta machine can be made with the addition of 2 more diodes, so that when the losses in the star configuration rise to around 40%, it will use the extra two diodes (from the star point to the + and - outputs, and this will convert the star to delta with no switching..... but then we hit an impedance mismatch because our stator resistance drops to a third of what it was.
You will have seen this when you open a 100A plus alternator... and find 8 diodes in the diode block, not 6.
So next we open the gap to stop stalling, but this degrades the alternator at the same time, or we could add resistance to the line, we miss out on some power, but take some heat out of the stator, and allow the blades to run better.
We can get out of some of this by upping the voltage and poles, and using a transformer.... this can be quite cunning, as we can tap change with triacs, and we can wind the transformer to emulate a battery charging transformer by making loose coupling with plenty of leakage, this will help match the prop to the air, and shift the heat out of the stator to some extent, and if the mill has an iron core (motor conversion, radial iron core (AWP, F&P etc)), we can mitigate some of the effects of armature reaction, and match the loads much better.
In fact we could emulate a full blown mppt with a jump table,lower leakage transformer and a bunch of taps and triacs if we were keen, and liked rats nests.
What I'm getting at is we can get hung up on alternator design. If we build an mppt (analogue or digital whatever), we can use virtually any old thing and match the load to the air.... then it's simply a matter of how powerful we want..... general rule ... for a fixed rpm, bigger is betterer for more power. More rpm (speed increaser makes them smaller again)..... back to angular velocity I guess for fixed flux.
Things that get lost from time to time.....
Every turn of wire in the coil has it's own vectors with relation to the field changing in it's vicinity. All those vectors add up to the final emf in that coil at any time in the cycle.... in fact at top dead center, the total emf vectors add to zero.
With axials, the legs are not points, but spread across an area... all seeing the flux differently. So magnet size, leg width, hole diameter, coil height, area, magnet spacing all effect the outcome.....and the list goes on.... the only thing we need not worry with is the armature reactance. The synchronous impedance will be pretty close to resistance for our purposes.... and we know we need some resistance so the voltage can rise in the coils so the prop wont be in hard stall from the get go... or mppt.
We should know or be told....... that we cannot design an alternator on it's own. It is part of a symphony. All things must be taken into account if we don't use mppt, but we can build a darn good machine without it to.... but then it has to be part of a team.... not a solo player. Mppt takes the skill out of windmill design.
Personally, as an owner/builder of a few quite powerful axials, and a not so innocent bystander to a radial flux machine, now (hindsight is cool isn't it) I would want an iron cored radial any day of the week, even with (and I WANT) oodles of armature reaction (Flux rolls eyes).... and ferrite magnets (eyes roll again).
Still the best, toughest by far, bullet proof home powering mill I have been in contact with is the AWP HV transformer coupled unit with the rewind we did for it.
That thing is fairly well matched, and burn out proof (thanks to the reaction component)... and the magnets don't degrade either :)
End waffle
..................oztules
Edit:
I just can't get excited with efficiency when I'm not paying the bill for the wind.
Stator efficiency for finding the watts lost for the sake of heating I have to be interested in.
System efficiency pales into insignificance compared to matching the items to the wind.
Paying for fuel makes it a whole different ball game.
-
after re reading a good few times i,m thinking i,ve got to stop licking things to see if their working .... ???
Artv might come back with some details and any progress to date ?...
interesting reads there for sure ....
-
Not to answer for Art, but the alt he is messing with is a large frame delco rewound, with a big neo in the rotor. It's
been a while, but it had as many turns of #14 per coil as room would allow. (over 20)
He got it from me. (how I know)
-
Not to answer for Art, but the alt he is messing with is a large frame delco rewound, with a big neo in the rotor. It's been a while, but it had as many turns of #14 per coil as room would allow. (over 20) He got it from me. (how I know)
bj,
Do you have any specs, like rpm vs watts, for this rewound Delco?
-
Windyone: sorry to say, only from memory. The data was lost when lightning hit the shop. (puter fried)
From memory, cut in was just below 300 rpm, into two D8D's in parallel. I think the most I saw was about
40 amps. That was in a ridiculous wind. Five foot diameter blade set.
It worked, but it wasn't impressive.
That fact, as well as no wind here anymore, is why I gave it away.
Art could maybe give better data, but not sure if we've heard from him in a while. (hope he's OK)
-
Hi BJ, and All
I've moved on from that ,but did testes for about 2 months..too much drag.
I was shorting the coils ,trying to catch the voltage spike (when you remove the short), and was told that you can't ,because it happens too fast?
Am currently able to catch them and pulse charge super cap bank,
Just having problems with making a consitent cap dump switch,
Do a fast switching short,feed that to a X ,feed the 2 leads to a diode bridge.
The beauty is you can hook multiple transformers(X) ,multiple cap banks.
Am using a 4 brush dc motor ,just shorting 45dg off brush location.
artv
-
Glad to hear you are well, and still trying things, and learning Art.
-
Why has nobody seen how to tap into the coils of a permanent magnet motor or generator?
It seems to me there is unlimited potential.
I've run lots of testes ,you can collect , what seems to be endless,(haven't got that far yet) amounts of stored capacitive charge, which you can use to charge the super caps,which in turn run your device??
I'm just getting here now ,but am sure the amount of charging caps is more than one needs.
If I ever get my switch worked out ,you'll all be the first to know.
Thanks for all the help I've received........artv