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Renewable Energy Questions/Discussion => Automation, Controls, Inverters, MPPT, etc => Topic started by: solarnewbee on May 22, 2016, 02:21:42 pm
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Good Day All!
I'm adding a windmill to my system in the Philippines to cover typhoon and monsoon season and it's a 3-phase as unit with rectifiers added just before the MPPT controller to keep the wire size down. this windmill does not have a way to slow it down like feathering or braking.
the manufacturer recommends a dump load that will pull the motor down to safer speeds. I have ordered an ats charge controller for it to transfer automatically. I just don't know what a dump load is, beyond maybe 12v water heating elements in series on a water heater(also mentioned by the mfr). not really any electric water heaters in the Philippines but i can get the elements from the camping/rv supply house.
If someone has an idea and wouldn't mind drawing a picture or detailed idea i would appreciate it.
Best Regards!
SN
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You don't specify the capacity of the machine (watts/kilowatts and/or voltage).
My own wind turbine has a 3kW loadbank which is basically just a big metal box with lots of ventilation holes, and a whole lot of thick resistance wire inside. Mine is a 3-phase load, which is used on the input side of the controller (AC side) where it's more effective and less likely to be affected by component failure.
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sorry Ross,
it's a 2400 watt 24/48v PGM motor
If your resistance load is there all the time won't that subtract from wattage or am I missing something.
can you draw me a picture (flow diagram)?
thanks, SN
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it's a 2400 watt 24/48v PGM motor
OK, so it's a managable size. If it was a 300W toy, or a 45KW+ beast, we might have had to reconsider :)
If your resistance load is there all the time won't that subtract from wattage or am I missing something.
The controller has a large, double-pole relay that kicks in when the battery voltage is above a set point, somewhere around 55V
When the relay kicks in, it closes the two remaining phases to the two remaining pins on the dump load, in effect putting three resistors across the three phases, and loading the turbine down quite heavily.
Because they're on the AC side of the bridge, it doesn't draw anything from the battery except what is needed to power the relay, possibly.
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Thanks Ross! Got it.
Now the Mfr's instructions say that my 11 blade windmill should not be under this kind of braking in extreme winds (typhoons) so I may have to engineer something simple like they use on windmills on farms like grandpa had. Pull a lever and the tail fin folds sideways.
thanks,
SN
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hi Solarnewbee
its a modified car alternator windmill ......much like ( if not the same as ) sold by companies like " Missouri wind and solar "
thats not to say it wont work in your situation ..... it has a few fairly large neo magnets that can burn out a coil in a storm
i dont think anything will protect it , the blades are designed to go into stall or " flutter" mode ....thats a bit iffy at best
but Grandpa usually knew best ......theres the nub
dont let it run in a storm .......take it down i guess ?
but then ...i,m a wuss :) ......
taking it down in stormy weather and living to fight another day may not be a bad option .... and good luck , whatever you decide...........
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sorry :)
i should have added ....tail furling ...
it works to protect the mill ....its simple and effective......and will protect the alt
oddly ...its hard to find a good video on utube explaining it ...this is the best i could get
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Best description I've seen is here
http://www.thebackshed.com/Windmill/Docs/Furling.asp (http://www.thebackshed.com/Windmill/Docs/Furling.asp)
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that about summed it up ......Frackers link :)
so a combination of the two then maybe .....
furling and a dump load of whatever you can get your hands on that might work ..... (a custom 12/24/48v water heater element ,an air heater ...even bits of old tumble drier elements rewired if need be ......)
but the resistance of the dump load needs to closely match ( and ideally exceed ) the mills maximum output......ohms law is a pain , but you want to do right by your mill ....
furling is an interesting concept , i,ll give it that .....but once you try to set it up the penny will drop
this is my mill fully furled .......on the ground .....not ideal.....but it looks furled ??? ...and somehow that makes me feel better as i,m still trying to give it purpose in life :) ...all fun
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but the resistance of the dump load needs to closely match ( and ideally exceed ) the mills maximum output......ohms law is a pain , but you want to do right by your mill ....
I hate to be a nit-picker, but especially for someone who's new to the game, this needs to be clarified.
The RESISTANCE needs to be matched to the turbine. If the resistance is too high, you won't pass enough current to make an effective brake. If the resistance is too low, you will dissipate most of the generated power in the alternator (and potentially burn it up). Once you have the right RESISTANCE established, it must be of a sufficient POWER rating to dissipate all that generated power without itself burning up or making a fire hazard.
Eg, if your alternator has a nominal output voltage of say 26 volts, then a load resistor of about 0.75 ohms will cause 34 amps to flow, and will dissipate 900 watts. We're talking about a resistor like a toaster... it will need to be even bigger if you don't want it glowing red! (or water-cooled or similar)
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your so cute i love you
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the Resistance has to higher ......otherwise how would we stop the thing ... the Resistance has to be higher .....otherwise everything would go to pot
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ah well ...a melt down ......no one gives a $#!+ about windmills anymore ....but they have their moments........
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Hey all! Good Day!
Just for clarification mine is a Dual PMG, differences pictured below, not an alternator designed for 24v parallel or 48v in series. It's 2400w 11 blade rig and the PMG generator is longer to accommodate dual 3-phase coils.
Niall do I need to build enough resistance to stop it or just braking down to a reasonable speed. I just want some resistance braking until wind speed get up past say 40mph nearly tropical storm levels.
for my own peace of mind I will probably set the pole with a hinge to take it down for typhoons and maybe figure out a simple angled furling hinge in the distant future.
thanks for the great discussion guys,
Sn
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Hi Solarnewbee, you will need to match the dump load to the generator size. Your regulator will be a Shunt regulator, which means that when the batteries are charged it sends the output of the generator into the dump load. If you don' t have a dump load the turbine would just unload when the regulator cuts in and destroy itself because of the speed it would be running at. In a solar setup the regulator just open circuits the panels, but doing that with wind or hydro will just destroy the turbine in high winds or just by water pressure .
You will have to find a dump load capable of taking the current your generator will supply. If you are using it at 24 volts you will have to be able to sink 100 amps into it, at 48 volts you will be sinking 50 amps.
Power = Volts X amps or more useful for you Power = Current Squared x Resistance.
So for a 24 volt load you will need 0.24 ohms as a load.
For 48 volts you will need a 0.96 ohm load.
Making sure that your load can handle the current will be the challenge.
A water cooled load dump would be the easiest to make.
Pete
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Hey Pete,
My charge controller has a built in ATS to switch to an aux bank of batteries or in this case a dumpload. Question is should I put the dumpload on the ac side to rule out possible rectifier failure or trust the rectifier will hold out under a load? A 3 phase dumpload will require what kind of wiring design pictured below?
As far as water cooled goes I could use a small rv water heater and 12v heating elements in series on the dc side or I could buy Kanthala wire and wind on ceramic poles in delta fashion on the 3 phase side for each internal pmg since it is a dual pmg. The aux output would have to operate 2- 3 pole contactors to channel the 3 phase to the dumpload but not cut it off otherwise I would lose power to the charge controller and.... restart.
?The 24 volts stays consistent throughout?, I want to ensure the charge controller is unaffected during resistance braking.
Thanks Pete very helpful!
SN
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Star or Delta makes no difference in function. In Delta, the phase-to-phase voltages are higher so the resistance of each element will need to be a little higher for the same dissipation.
You don't need 3-pole contactors/relays, to switch in a 3-phase load.
There are three phase-wires, lets call them A, B and C.
When all three are connected, you will get voltage (and therefore current) between AB, AC, and BC.
If you disconnect any TWO wires, lets say A and B, leaving C connected - you cannot get any current flow between any two. (AB has both wires open circuit, AC has the A wire open, and BC has the B wire open).
You can use MUCH easier to get and less expensive relays this way.
As a dump-load is in no small part a "safety" device, it should go on the AC side - ie, before the diode bridge.
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" do I need to build enough resistance to stop it or just braking down to a reasonable speed "
two scenarios may apply here....ish ..i think...i,m usually wrong
one....its a stormy bad night ( but no zombies yet ) .... you want to let it run , and need the charge ...then a pwm dump load controller with furling will ( should ) balance out ......fast but scary ....its on the edge
two ....windmills are anything but predictable and you can,t really thrust them .... ( things that go bump in the night and such ) so hitting the short switch ( the ultimate dump load ) could save the day and freeze the mill ......
but only certain mills will accept a hard short on the alternator and survive the instantaneous internal load .......
the mill i have is a standard Hugh Piggott design and will tolerate that kind of shutdown , once you hit the kill switch it stops ,
with a radial design alt like you have Solarnewbee i,m not sure that electronic braking will work ......
maybe use extra safe furling ( Frackers link ) and ignore those high winds ......
ps ....on shunt load selection .....a tristar c 60 controller that i have recommends a minimum shunt load exceeding 20% of the mill capacity , thats a fair bit .....i need to check the manual, but from memory thats it
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Hi Solar, just had another thought on your wind mill. First the dump load is only there to stop overspeed in the event the batteries are fully charged and the regulator disconnects them. It is not going to work for hurricanes or typhoons, the only thing to do if one of those is on its way it to lower the tower, otherwise it will be destroyed.
The simplest way to run the load dump that I can think of is to, Connect a Three Phase contactor to the AC output of the wind generator. You could just run three wires off the input to the regulator to a contactor. Get one with a coil that is the same as your battery voltage , eg 24 volt ( available as an option normally) or 48 volt.(you may have to use a regulator to drop the 48 volt to 24 otherwise rewind the coil to suit 48 volt)
The regulator you have sounds like it has a connection for the dump load, just take the output from the regulator dump terminal and connect the coil of the contactor to it.
That way when the regulator switches the batteries off it will energise the contactor, which wil connect the three phase AC from the wind generator directly to the dump load. When the regulator switches back to charging the batteries, the contactor will drop out and the batteries will charge as normal.
You will need a fairly large contactor, that is designed to be used in Motor Starters.
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Hi Solar, here is a mud map of what I am suggesting. Make sure the contactor can take the full load current of the wind generator through its main contacts.
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just to echo Petes comments Solarnewbee....and i dont live in a typhoon area......( far from it ) i,d tend to think about taking the mill down when the elements are conspiring against you ....
i live relatively near the atlantic coast and its a graveyard of windmills ....its not their fault......a kind of gruesome tour along the west .....
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Hey all!!!
Awesome responses and thanks pete for the drawing, I love me some pictures. I had already bought several 3-pole 24v coil contactors that handle 60 amps, they are inexpensive at the supply house since I do a lot of hvac and ac&r work.
Since my 24v PMG generator is DUAL I will double up your drawing pete. Also, do I make a .24 ohm winding for each winding in the delta? and what do you think I could find to wind the kanthal wire on short of rewiring a toaster ha?!, that might just work too, goodwill has them for $2 all the time.
niall: I will be mounting the windmill 20 feet off the top of a 40 foot long balcony so I'm going to rig a hand crank my daughter can use (when I'm not there)to crank it down when winds get above 45mph.
Thanks guys,
SN
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dalm.....i guess i,ll have to put the mill up again
its good to see someone trying things with mills ....
to be fair to it .....it never looked good on the ground anway ... :)
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So guys,,,,
Anyone know if these ( 1 ohm? )will do the job wired in delta form bolted to a heatsink?
http://www.ebay.com/itm/1-2-4-8-10-Ohm-100W-Watt-Shell-Power-Aluminum-Housed-Case-Wirewound-Resistor-New-/141957695607?var=&hash=item210d568877:m:mTihmKm-hBqIO03-aYwyRmw
Thanks,
SN
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backing up a little bit .....
is the mill 24v or 48v ?......
probably the easiest option is something like one of these ....
www.ebay.ie/itm/24V-DC-900W-IMMERSION-WATER-HEATER-ELEMENT-WIND-SOLAR-BATTERY-24V-POWERSUPPLY-/361590161217?hash=item543073ff41:g:h5kAAOSwv~xXD--f
most water low voltage heater elements allow you to rewire for 24v or 48v at 900w dissipation...
the mill looks like it has a 1M ( 1m2 ) swept area......so one of these ( with a dual voltage wiring option ) would be enough..........
for extra headroom ( an option ) you could use two elements in parallel with a tristar c60 ( or similar spec pwm unit ) set in diversion mode ......
http://www.morningstarcorp.com/products/tristar/
i dont think you will ever see 2.4kW instantaneous from the swept area you have ,.....
one 900w water heater element and safe furling will do it .....ish ...i think
furling is the key :)
mmm...the element pic has only two connection points , they usually have four ....so 2 in parallel fot 24v ...or series the pair for 48v
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Hey niall,
My mill is 24v dual 3 phase so I need 2 dumploads so both coils will have something to bite into. Those elements are almost $60 each with shipping. I have the charge controller that has automatic transfer to alternate load when batts are full. I have the 3 pole contactors 24vac coils, you think they will be fine running dc continuous? hvac and ac&r systems usually run as high as 28vac anyway and they are rated continuous use coils. I'm curious to know the ohms on those 900w heating elements.
SN
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:)
i have very little idea ......ohms law was never my strong thing , but i asked the internet to be sure ...ish
the resistance of the 48v 900w element comes in at about 2 ohms ....this makes sense in reality .....
my mill is rated for 1k at 48v , so 20 amps to dissipate and let furling take care of the rest ( in theory )......but one element on my mill ( when its up ) is a bit close to the bone ....
two in parallel would be safer .... the mills tail is too light and goes on a sponsored walk in high winds , ...so its not so much of an issue
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