[time-nuts] Li-ion Batteries

[Mark Sims]

I built a switched capacitor balancer.  It takes some time to balance a wildly out-of-balance pack but does a great job of maintaining balance during charging and discharge.  I run the balancer during pack charging and discharging.  I tried it charging an 8S LiFePO4 pack with 7 fully charged cells and one fully discharged cell and it worked fine... no cells were over-volted during charging.

It does not waste energy/generate heat like a resistive balancer.   An inductive balancer can handle higher balance currents for very high capacity packs, but is also quite a bit more complicated to do correctly.  Also built a processor-per-cell BMS using ATTINY-85's.   I've used both on  4S32P / 8S16P A123 packs and ICR 18650 packs.

Those A123 cells can dump 200A (each!) into a short circuit... you REALLY don't want to short a 32P A123 pack...  They are also rather tolerant of abuse.  A friend made a video of charging one at a 100C rate and it survived without exploding/melting.  I once bought some that had been sitting fully charged for over 4 years and when tested still retained over 80% of the charge.  A couple of charge/discharge cycles and they performed like new.  I keep  4S1P packs in my cars for jump starting.   There is a video of a guy in Canada staring his car over 10 times in sub-zero weather using one.  The cells are 26650 size... are about the size of a D cell.


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> The BMS doesn't balance the charge after charging (which consumes time & energy