series or parallel

[dutchlincoln]

Hello,
i might be able to aquire some 18650V cells soon.
Now, i wonder: when building a pack, what's advisable?
Put cells in parallel first, and then these cells in series, or is it better to go in series first, and then make parallel sets out of them?

thnx.

 

[spkpn]

from what I have heard, putting parallel blocks in series is the way to go. However, I dont know the reason for that.

 

[fivari]

Well, one goed reason is: if you put in series first, you will need a BMS for every string you make or at least wire all batteries individually to connect to a central BMS.
Another reason: if one cell fails, the whole string will fail. Whereas, if you put in parallel first, the other parallelled cells will compensate.

 

[Ypedal]

The short version :

Mostly... when using small cells ( 18650's ) , it's best to parallel them into a group to form a large P group thens series those.

when using large capacity cells ( like on an EV with 100ah cells ) , it's prefered to series them and then make parallel strings with BMS protecting each single cell...

 

[dogman dan]

You might also want to make each paralell cell group fairly easily disconnected from the others. So if one group develops a problem, it's not buried in the center of the pack, with tons of hot glue , and spot welded strips to dig through to fix it.

Make it so you can repair if needed, by removing a cell group and slotting in another.

 

[dutchlincoln]

All great ideas!.
Basically: i have to wait until i have all the cells that i can get, in order to be able to calculate how many parallels i can have...

At work, we have a project where we buy battery operated tools for, and ditch the battery packs, and connect the battery-operated tools to a large power-supply.
I don't know exactly how many tools wee need, so i can's start fabricating yet...
pitty, it put's a real stress to my patience..