Quote:
Originally Posted by Ecky
Care to give an example of an LED balancing array? And, how would one go about calculating the correct resistor for protecting a lithium battery from too much current? Chances are good I'm going to build this in the next month or two.
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Probably not the correct way to precisely calculate this, but I just used ohms law to determine what size resistor made sense.
Determine the maximum acceptable charge/discharge rate for your battery. I used charge rate since that was the most limiting factor. Lets say you have a 5 Ah battery with a 10C charge limit. That's 50A max.
Now estimate worst case what the voltage difference will be when your battery is at the most discharged state, and subtract that from the max charging voltage. So maybe my battery drops to 8v, and the alternator can charge at 14v, for a 6v difference.
V (voltage) / I (amps) = R (resistance)
8v / 50A max = 0.16 ohms.
I'd round that up to 0.2 ohms and find a resistor that can dissipate up to 40 watts, though it probably doesn't need to be able to handle that continuously. Mount it to something metal so it doesn't melt anything should it overheat.