Making up some series parallel arrays.

[opampsmoker]

Hi,
We have a load of used lithium cells that we wish to build up into series parallel arrays. We will just charge them all up, and put them in series parallel. Will there be any problems? We wont bother with any resistive "balancing" between the cells prior to paralleling them. Will we be OK?

 

[BradtheRad]

used lithium cells

There's the chance a weak cell is driven into reverse polarity by surrounding cells. It partially or entirely drains the entire battery pack.

(Li-ion cells are the type prone to fire and explosions if abused... Not sure about your situation.)

Problems can be avoided by regular testing of each and every cell individually with a voltmeter.

Or, put a diode inline with each string. Then no strong string can discharge into a weak string. However one weak cell can still be driven to reverse polarity by strong cells in its string.