1S LiFePO4 BMS

[ThermallyFrigid]

I have a project that uses single cell AA size LiFePO4 cells to power a blue LED
The circuit also consists of a QX5252, axial inductor and small solar cell.

I want to use a small 1S 3.2v BMS to protect the cell from overdischarge.
However, when I look for such a BMS, they are all set to 2.1v for their overdischarge cutoff limit.

I want the cut-off higher, at 2.6v to 3.0v for the LiFePO4 cell.

I am wondering why all manufacturers for 1S, 3.2v LiFePO4 BMSs' would have the over-discharge limit set so low that damage will occur to the cell after repeatedly dropping to that voltage?
Why not set it at a safer (for the cells lifespan) voltage?

[Peabody]

The same complaint is often heard about 3.7V protection circuits.  Many suggest that 2.54V is too low for overdischarge, and the battery may be damaged.  However, there are probably hundreds of millions of lithium ion and LIPO cells out in the world protected by the DW01, which has the same shutoff point, and apparently most do fine.  One suggestion is that these protection circuits are only emergency shutoffs, and your circuit should provide a separate "normal" shutoff at a higher voltage.

There is an alternate protection IC for 3.7V lithium with overdischarge at 3.0V, the part number of which I can't remember at the moment, and maybe something similar is available for your LiFePO4 cell.  But if not, in theory you could use something like the DW01 in combination with your normal BMS, which would give you at least 2.5V instead of 2.1V.

Actually, they now make protection ICs that move the mosfets into the chip, so the entire circuit is now a very small three-pin IC, a capacitor and a resistor.  XB7608A and FM5056 would be examples.

[tunk]

Would it be possible to use two BMSs?
- Li-ion for discharge
- LiFePO4 for charge

[mariush]

Monolithic Power Systems have some charger ICs which have configurable undervoltage levels through i2c

For example, MP2664 and MP2667 are lithium chargers that have the battery undervoltage configurable between 2.4v and 3.1v (defaults to 2.8v) . Technically they're lithium-ion charger chips, but the charge voltage can be configured between 3.6v and 4.545v so technically if you set the charge voltage to the minimum of 3.6v you could charge the LiFePO4 cells.

MP2664 https://www.digikey.co.uk/en/products/detail/monolithic-power-systems-inc/MP2664GG-0000-Z/18089944

MP2667 https://www.digikey.co.uk/en/products/detail/monolithic-power-systems-inc/MP2667GG-0000-P/11610986

Also MP2710 is worth the mention, though it's less hobbyist friendly with the bga balls : https://www.digikey.co.uk/en/products/detail/monolithic-power-systems-inc/MP2710GC-0000-P/25543918