DUMP LOADS (wind mills)

[solarnewbee]

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

[rossw]

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.

[niall]

" 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

[Pete]

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.

[Pete]

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.

[niall]

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 .....

[solarnewbee]

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

[niall]

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 ...

[solarnewbee]

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

[niall]

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

[solarnewbee]

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

[niall]

 

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