Dual Lithium Battery Charging / Management ICs Topology?

[Chendy]

Hi,

I want to charge a couple of 18650 lithium cells, connected in sort-of-parallel to provide double capacity. I dont want to rely on cell matching, so want to use a couple of linear charging/management ICs. I also want 'pass-through charging', the ability to power my load and charge the batteries simultaneously, when plugged in to the charging source.

This low cost BQ21040 looks of interest. (if anybody has any other recommendations please lmk)

Is it possible?.. how would I got about connected this up? Like the picture below?:

[Siwastaja]

Just parallel the cells properly. No special matching needed, just don't use completely random or totally crap cells. Match the voltage once, when you first time weld the cells together.

This is exactly how 18650 cells are designed to be used.

Your complex scheme is asking for disasters.

[Chendy]

Okay great.

But the problem is planning not to weld them together. But use a simple 18650 holder...

hmmm

[Siwastaja]

Oh, 18650's are definitely not meant for that. Those holders serve a purpose (for example: a low cost item for hobbyist cell analyzers/testers), but it is absolutely not OK to let end user insert loose cells into those holders, using them in an actual product. Unless it's for yourself only and you know what you are doing. (Using these as generic holders will result in a shorted cell and a melted holder after some usage.)

This holder thing should be some kind of a FAQ item, it pops up all the time.

The only way 18650 is designed and supposed to be used is to be welded to make a pack.

If you want user-insertable battery, the only acceptable way is to weld the 18650's in parallel, add some sort of casing and a connector. A fuse inside the pack is a good idea.

The possibility to insert two cells that are then paralleled is an extremely stupid idea and requires rather complex circuitry and algorithms; to the degree that the fact that people ask about it here is often a good sign it is too big of a task for them . It provides no benefits, either; there are only downsides. That's why it's never done.

Don't do it the weird and complex way, do it the way it's designed!

[Chendy]

Great thanks, valuable input!