18650 4.2V to 20V

[SentinelAeon]

Well after what you wrote down i know it will not work. I have a problem. I am using a 21V 5S charger from ebay. It says 21V but in reality its more like 20V. And BMS also cuts off before 4.2V. So it is basicly useless

Well, as far as charger goes it would work if cells are badly unbalanced as that 21V would get some cells to 4.2V if others are lets say 3.8V. BMS says it cuts voltage between 4.23V and 4.28V but i am pretty sure it cuts sonner. This is the BMS i use:

**broken link removed**

Btw i just thought of something. I know this is "against the rules" but ... cells get unbalanced in time. So i would need to balance them only like i dont know, once a year ? Or maybe once per half a year ? I have plenty of step-ups at home so unlike my lithium charger, i can get pure 21V. If i connect that to speaker, assuming BMS will allow cells to go above 4.20V, it should work. And i just leave it connected for a while, like few hours. Now i know using DC adapter instead of charger is wrong but, can few hours of it being connected really do something bad to batteries ? Anyway this is the only solution i can come up with.

 

[audioguru]

Maximum charging current of 25A (!) is crazy for 18650 cells. 3A max is reasonable.

 

[rjenkinsgb]

If any one cell significantly exceeds 4.2V due to others being undervoltage, there is a chance of a cell bursting or catching fire.
Per-cell voltage limiting is absolutely vital.

Why not just get a combined protection and balance board - they are cheap enough, eg.
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[SentinelAeon]

Because if i get this combined one i still havent solved the problem with my charger only charging until 4.10V. So this balancing will still not kick in. As for any cell exceding 4.2V, my existing BMS protects them from that