A battery and charger has finally arrived from Hobbyking.
The LiFePo4 battery is rated at 4.2Ah at 13.2v, with a max charged voltage of 14.4v. It has a sustained discharge rating of 30c (126 amps) and a 40c max (168 amps). The recharge rating is 2c (8.4 amps).
I used
this balance charger to discharge the pack to 12v, and then balance charge it to full capacity. I was happy to see that even though I didn't fully discharge the battery, it still took 4.3Ah charge.
Next up, I need to find a power resistor that will limit the charge rate to 8.4 amps. I'll assume my battery will not drop below 10v, and the alternator will not put out more than 14.5v, for a 4.5v difference. Ohms law R = V/I says that I need a 0.5 ohm resistor to limit the charge current.
I'm just wondering if this is the right way to go about doing this, and I also wonder if limiting the charge rate is even necessary. I'll do some testing to find out what some real world charging rates look like with, and without a limiting resistor.
It's a shame that the battery is limited to a 2c charge because the 30c discharge capability is not utilized. Perhaps I could make separate charge and discharge circuits using power diodes.
I wonder if I could use
this diode for the charge circuit, and
this diode for the discharge.