My ride on mower needed a new battery. For about half the cost of the cheapest lead acid battery I could find I purchased 4 14Ah LiFePO4 cells. Mucked around with them a bit then when I thought they were top balanced and reasonably charged tried them in the ride on mower.
Initially the mower engine must have been at the peak of compession cycle and the cells, less than fully charged, had a tough time getting the engine to crank. But once the engine was past the peak compression point the cells had no problem starting the mower.
As I mowed I kept an eye on the battery voltage. When it rose above 14v I got nervous I could be overcharging a cell since there was no balancing between cells. I shut down the mower, waited a minute then easily started it again. After stop starting a few times when the voltage rose over 14V I put the mower away.
Conclusion:
Even small LiFePO4 cells are suitable in the mower.
Some sort of voltage regulation is needed to adjust the lead acid charging regime to be suitable for LiFePO4 cells.
Next steps:
I have a programmable low voltage disconnect I can use "backwards" as a proof of concept. The big P channel mosfets will help manage battery voltage. When the battery voltage is low, the mosfet is on allowing full current in either direction. Once the charging voltage hits say 13.8V turn the mosfet off and allow the intrinsic diode to drop the voltage to the battery.
In the meantime I am waiting for some larger cells to arrive to help overcome the peak compression challenge. And a charge shuffling balancer to ensure that when I go to mow the lawn all the cells are at the same voltage or state of charge.
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