Enginyr, I think you are going to need to move to a 6 cell battery and step your voltage up to 5V to make this work better. I'm assuming your configuration is 2S2P? 3S2P would get your fans to the needed CFM, then a simple resistor will step down the voltage for your LEDs.
Sizing your resistor is simply a power funtion I^2 * R or V^2/R. I'm going to use the V^2/R.
First you'll need to determine a value for your resistor:
5V battery - 3.4V LED = 1.6V drop in resistor.
Since we know the LEDs are requiring 13A, we apply V = I*R and get:
R = 1.6/13 = .123 ohms - This is not a normal resistor value, so we'll need to make it from some parallel or seies resistors. I'll go with parallel. If using all the same value the resistors parallel rating will be R/Number resistors. So: 5 X 0.63 ohm resistors in parallel will work. So will 8 X 1 ohm resistors in parallel.
Now for the Wattage requirements:
We know P = V^2/R (The I^2 *R yields same result) and we know V drop on the resistor bank is 1.6V. We also know R is ~.123.
So you'll need a resistor bank rated for at least 21 Watts. Since the power dissipation is divided equally among parallel resistors the wattage value needed is:
Wattage of bank/#parallel resistors.
So if you use 8 X 1 ohm resistors, they'll need to be 3 watts or more. If you use 5 X .63 ohm resistors, they'll need to be 5 Watts or more.
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If it is broken, fix it. If it isn't broken, I'll soon fix that.
