I started building some 18650 batteries. I'm quite familiar with almost every about them but I'm not sure of one thing.

I know that when charging one 18650 cell the cutoff current is around 50ma + or -. How does that translate when you have a large bank. Say you have 10 in parallel. You could assume that would be 10 x 50ma, or 500ma. But what if you have 100 in parallel? I wouldn't think that you would stop the charging when the current gets down to 5 amps?

How does that work out with such a large bank?
How does it work when you have a large series bank also?

Any thoughts on this will be appreciated!

Thanks, Ken

 

Thanks Cody, it's something I've looked into and cannot find the answer to. I'm curious how it should work out..

 

I am not sure about it but i am looking for the answer for you then i found it i will message you.

 

I've been looking into it also for a while. Haven't found anything yet. I thought there might be a formula for it.

I appreciate anyone else looking into it. You would think that the guys building large power walls with 18650s might know from experience.

Ken

 

That is why you should NOT put them in //.
Without their own means of protection in each string.
You cannot guaranty sharing, even when brand new.
An engineer asssumes all the current goes in one cell only for WCA.

 

That is why you should NOT put them in //.
Without their own means of protection in each string.
You cannot guaranty sharing, even when brand new.
An engineer asssumes all the current goes in one cell only for WCA.

Sure, I'm familiar with that. I use 3 amp per cell fused buss in any parallel string. I'm talking if you have even a 4S4P battery and each cells cutoff current when charging is 50ma. When charging a 4P battery is the cutoff 200ma? I wouldn't think so, but nothing I have read says.

 

I have been working with large battery pack of 48v, 36v 10ah to 50ah. what I have observed in most cases that the BMs and charger if they are not compatible with each other then the upper cut-off of the battery changes.

so for large battery pack whatever the configuration is the ultimate decision maker for the upper cut off would be BMS and Charger for the battery pack.