Resistance of dump load

[Jason Wilkinson]

 Hi to all, my buddy has to come home every day to shut down his turbine for fear of overcharging his batteries. his is 48volt system,   ten 220 watt panels and a 12 footer turbine . most days he goes into float and absorbe, so he needs to "dump /divert " just bought a coleman c440-hva controller and two 300 watt 10.4 ohm resistors  i've seen 30 to 35 amps from the turbine .  Are these resistors enough for a dump load or do we need more   
  Thanks  Jason

[Mary B]

Ohms law volts/amperage = resistance needed. need 1.25 ohms at 1750 watts (I rounded the resistance down from 1.37 and wattage up from 1680 to more common values). Are the solar panels on the same charge controller? If so those values will have to take into account the power that they can provide also. I calculated for the turbine only. Ohms law will give you these values and is something good to learn

[Flux]

As Mary said, it depends on what you are doing, it seems as though you have a controller that deals with the solar so you only need to divert what the wind produces, in which cases the resistance he gave you will be fine.

Unless you have a wind turbine that can be shut down you are more or less stuck with that option. If the turbine has a means of shutting it down you seem to have enough power to justify shutting the wind machine down when you reach absorb volts and let the solar finish the charge.

If it is a furling machine with short circuit brake as the only means of shut down, I would be reluctant to use that as a shut down method unless you are absolutely certain it won't get away from the brake under any wind condition, safer to leave it running and dump the power although it will need expensive resistors and you have a lot of heat to deal with.

Flux

[Jason Wilkinson]

HI  Maryalana,  i see you gave me figures for dumping at 50 volts and not 52 (closer to full  charge)  our 10.2 ohm resistors are only 5.1 in parallel  we still need  approx,3 ohms (rounded figures
   Yes Flux the panels have their own controller,  from the manual , the coleman 440  has it's heavy duty solenoids and  diagrams show batt not connected DIRECTLY.   I know this forum do not recommend such
  Jason

[Mary B]

Actually I used 48 volts, close enough for a calculation like this but yes, base it on peak voltage off the turbine. It was more of an example on how to do the calculation. There are lots of online calculators too but I learned ohms laws ages ago before the internet and personal computers.