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Old 08-01-19, 01:03 AM   #2
NiHaoMike
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From a quick search, it looks like 1S LiFePO4 BMS boards are hard to come by, but 4S LiFePO4 BMS boards are really common. If the 4 cells are closely matched, you can just go for a 4S pack, would also make the rest of the setup easier to design. Otherwise, you can use a standard 1S BMS for overdischarge protection but the trip point will be too high for overcharge protection.

For a boost converter, just find one that can supply well above what you need (I suggest 4A or more) with a low idle current. I'm not sure of any ready made modules to recommend since I generally build that kind of circuit from individual components. You can try a board for a portable USB battery, but the built in charger will not be usable without modification to limit the charging voltage.

For a charger, you'll need a MPPT step down if you're planning on using a standard 12V solar panel. (Or look into building your own with about 3.6-4V MPP voltage - that's surprisingly economical for your use case since the cost per watt of small panels is way high.) A shortcut that helps us is the fact that LiFePO4 has a pretty constant voltage over a good part of its cycle, so a 555 timer driving a buck stage with a fixed duty cycle combined with another circuit to switch it off if the battery voltage reaches 3.6V will do the trick.
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