Running 2 different Li-ion batteries in parallel ?

[Jil]

Hello,

I want to run 2 batteries in parallel on my ebike, both home-made :
- 52V, 14S-6P & 14S-4P.
- identical BMS for both batteries : 35A, single port (for charge and discharge).
- identical cells (Samsung INR35E, 3450 mAh).
- the controller is a Phaserunner, the motor a GMAC.
- I use my ebike between 20A and 30A battery output.

My guess is that there is no problem to run and charge them in parallel, but I prefer to check with ES first, in case I miss something :

Question 1 : is it possible to run them in parallel without risks ? Of course, before connecting them I know that I need to have them at the exact same voltage.

Question 2 : when charging, no problem to use one charger (4A) for both batteries connected in parallel ?

Question 3 : in case the BMS have slightly different settings for voltage cut-off, I think it's better to charge them a little bit below the max (ie. around 57.5-58V, instead of 58.8V), do you agree ?

Thanks for your help

 

[john61ct]

No such thing as "no risk"

but yes you should be fine.

My rule of thumb is within 0.1V per series count, so 13S can connect if within 1.3V delta without the surge being "too great".

Of course exactly the same is better.

Do stay on top of State of Health and proactively replace units as they wear, before signs become overt

the "weaker link" side will age the stronger one faster

and of course an internal short on one will drain the other very fast, shortening its lifespan dramatically, if not murdering both together.

Charging to 4.05Vpc is always healthier than 4.15V

Better to charge separately for balancing purposes,

just check the cells are getting balanced, might need to go higher voltage

at least every so often

 

[amberwolf]

Lots of discussion on this basic topic that may have useful info for you. Not all threads are relevant, and there are threads not listed there that would be. But you can tell by title more or less which ones would be useful.
https://endless-sphere.com/forums/search.php?keywords=parallel*+batter*&terms=all&author=&sc=1&sf=titleonly&sr=topics&sk=t&sd=d&st=0&ch=300&t=0&submit=Search

 

[Jil]

Thanks :thumb: