I fitted the silicon diode in parallel with the mosfets and ran into trouble. Once the mosfets turned off the alternator had trouble regulating with the reduced load. The alternator voltage rose and the mower shut down. I found that a resistor to ground before the diode eliminated the issue. With some of the proof of concept stuff behind me I'm going to build version 1. It will have the following characteristics:
- A number of parallel mosfets which when turned on allow the mower to be started and the alternator to directly charge the batteries.
- Once the battery voltage rises above the first set point the resistor bank will be switched across the alternator to help stabilize the alternator output
- As the battery voltage rises to the second set point the mosfets will be turned off and the battery will continue to be charge through a series diode with perhaps 0.6V of loss.
At this point the maximum charging voltage should be around 13.4volts. Combined with a charge balancer it should ensure no damage is ever done by overcharging the LiFePO4 cells. The state of charge should approach 90% at most.
I'm leaning towards using a micro controller instead of all analogue circuitry because it offers flexibility to alter parameters or add additional control mechanisms should I need them.
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