100 watt resistor for a dump load?

[schmidt farm]

can anyone tell me if these will work for a dump load for a wind generator

ohmite 270-100m-40 1ohm 100watt, if you put a fan behind them to cool them. i am not sure of there original intended use. they are  out of a very large battery charger. maybe they are not what i think they are either.

there is 3 of them set up in a bank.

thank you. Alan

[Flux]

They seem basically useful but you give absolutely no details to work on.

If they are 1 ohm and you apply 12 v to them they will dissipate 144W. They were almost certainly not designed for fan cooling and it's anyone's guess what their forced cooled rating would be. I would take the 100W as absolute, the resistor may take more if forced cooled but you may have trouble with the connections. Anyway fan cooling for a dump load seems a disaster waiting to happen in the long run. Many do it, their choice, but not my idea of long term reliability.

Flux

[finnsawyer]

If he puts two of them in series so they dissipate 100 watts total at 14.2 volts they should work fine as each one will only have to dissipate 50 watts.  He could then make up 20 such strings to put in parallel for a total dissipation of 2,000 watts.

[ZooT]

I've been meaning to ask,

Is that how it works?

series splits the wattage dissipated between the resistors in the series string, and parallel doubles the total wattage dissipated?

[ghurd]

Watts is amps x amps x ohms.

If you know the amps in a string, then that tells the watts.  

It doesn't matter if it is two 5 ohm resistors in series, or parallel.  Amps in that string and ohms of the resistor is all that matters to find the watts being used by the resistor.

G-

[finnsawyer]

But he doesn't have amps in this case.  As a dump load it would be voltage controlled, P = (volts x volts)/resistance, as the battery voltage to dump the power would normally be 14.2 volts and would hopefully not exceed that value.  In that case the current for each string would be constant and the power would divide according to the value of the resistors.  With each resistor dissipating 50 watts he would have a considerable margarine of safety if the voltage should rise above 14.2 volts.  That is, it could rise by 41% to 20 volts.  Apparently, to do the best job one would need to put in circuitry that holds the battery at float current and voltage and connect the dump circuit directly to the alternator when the battery voltage reaches 14.2 volts.  The mill would then have to furl before the dump voltage reached 20 volts in his case.  The dump load that he could build would be able to safely handle up to 4,000 watts before that point if adequate ventilation was provided.  

[ghurd]

We are talking about different things I think. 4000W for 3 x 100W resistors?

Plus for all we know the dump controller is a Sea 50.

G-

[finnsawyer]

I thought he had 40 resistors.  Well, the original posting was a bit confusing to me the way the numbers were run together.  That's the way it goes.  I guess he still learned something.  Have a nice day.