4S-2P versus 2P-4S battery configuration

[Mako]

For a 48v FLA battery bank, is there a recommendation on which configuration to wire the batteries?

Also, thinking forward to end of life, should/when a single cell fail, there should be lower fire risk (lower amp draw) in the first config.

 

[twistedtree]

For a 48v FLA battery bank, is there a recommendation on which configuration to wire the batteries?

Also, thinking forward to end of life, should/when a single cell fail, there should be lower fire risk (lower amp draw) in the first config.

For lead, go 4S-2P for exactly the reason you mention. It's easier to detect/diagnose a bad cell/battery. It also gets you some redundancy because you can run disconnect one bank if it's bad and run on the other.



With LFP you typically do the opposite, building Ah capacity by first paralleling cells into "blocks", then series wiring the blocks. This is largely motivated by the BMS that needs to monitor/balance each cell or block of cells. So you would build it 2P-4S giving 4 monitoring/balancing points for each 2P block. That said, it's not uncommon to build two independent banks for redundancy. Then you would have 4S-2P, with each 4S bank equipped with it's own BMS. The down side is that it requires twice the BMS equipment. This is for external BMS designs I haven't thought about it for drop ins.

 

[Mako]

Thanks for the input. I like the idea of being able to disconnect each bank independently, because even with just an intended single bank design you still get some redundancy.

 

[DDW]

Drop ins in series is a problem, and often not allowed by the manufacturer due to the balancing issues. Better to use a 48V drop in, which presumably has BMS balancing internally. There are some offering an external balancer, for series operation.