nicd charger for li-ion

[SentinelAeon]

Charging liion 18650 batteries with nicd/nimh charger is a big no. But i would like to understand why that is so, in what ways the charging is different for different chemistry.

Let's take a hipotetical scenario where we have a standard 4S pack with a BMS. The BMS has several protection functions, it prevents cells to go under 2.8V and prevents them from going over 4.2V. But the BMS itself has very high current limit protection, far higher than this cells can handle, it has no dedicated charging circuit. And we have a nicd/nimh charger that charges with constant current of 1A.

This scenario would not be adviced but i would like to understand why and what would be the negatives of charging in such a way. I hope you can help me understand this better. Thank you

 

[rjenkinsgb]

The BMS safety cut-out voltage should be slightly higher than the ideal full-charge voltage, it will over-stress the cells.

The correct charger would hold at the correct full charge voltage and allow the current to drop off (to ~10% the capacity, 1/10 C) then shut off until the cells discharge a few percent.

That constant voltage stage is vital for correct, safe, charging.

 

[SentinelAeon]

if we assume that BMS cuts off at 4.2V, then we are left with the other problem, namely that nicd charger usualy ramps up the voltage slowly, while liion will always stay at max voltage and keep constant current. Am i right to assume that if you were to charge liion with nicd charger, that would degrade cells fast ? Would it even charge them ? I can assume that its not safe, but is heat/current/voltage the only concern or is it something else, chemical maybe ?