BMS destroyed my battery?!

[goatman]

if they had a bluetooth bms like the Ant bms
you could set the lvc at 2.5v
program balancing to start at 2.8v

I've never heard of a protective BMS that bottom balances.

Only dedicated balancers ( marketed as "non-protective BMS") or node charging can middle or bottom balance afaik

> i think charging to 4.2v killed it

No way, that has a relatively minor impact on longevity.

Using second-hand cells is inherently risky even if only 1P

Given that many will be past EoL, putting them in parallel groups astronomically increases the odds of quick pack failure

even with rigorous testing of each cell individually and discarding the majority.

If you want a reliable pack you have to buy a known good cell model

new, Grade A from a reliable source

on the ant bms you can program it to start balancing at whatever voltage you want
turn it on, turn it off
its an easy way to do bottom balancing and pack maintenance
then turn off the balancing function til next time

time stamped
https://youtu.be/Z7M_kNB7ltI?t=646

if i bottom balance to 3.0v
thats my lvc
all the cell groups should hit 3.0v all at the same time under load
at rest they will bounce back to 3.3v/3.4v
like you say, stay away from the shoulders

 

[john61ct]

This looks like a good seller?
https://www.ebay.com/itm/313014455885

 

[m3vuv]

Yes this sub-topic is a derail as far as your case is concerned.

I believe your BMS did indeed murder your pack, but not due to the "4.2V is too high", that being stressful manifests by an overall reduction in longevity **long-term** impossible to quantify (or even notice) without rigorous testing using accurate equipment in lab conditions.

Note also, the BMS 99.99% of the time has no control over charging

nor should it.

The charger should handle the automatic termination, is not even aware the BMS is there.

THE BMS HVC functionality setpoint is much higher than normal charging, only there as a backup failsafe for when the charger's regulation circuitry **fails**

in order to prevent fires, last-ditch protection of the pack.

With a good charger, you can adjust the profile setpoints, ideally not just voltage but how long CV / Absorb cycle is held before termination.

i would guess the buggered 7 groups had cells on there last legs and were rated for low c discharge rating,then 1 or more started leaking electricaly bringng the others down to a soc low enough to kill them.