LiFePo4 batteries 2P16S vs 3P16S and 16s3P charge issues

KenMorgan

so after running a 2p16s 20kw pack for about 3 months and all of the fun and associated issues that crop up in a homebuilt battery pack, I finally had the pack settled out.  

I then I decided to add 16 more cells to make a 30kw pack (@50 volts w/50-54.4vdc range).  

Initially I added the 16 cells as a 3p16s setup but after a couple of weeks noticed that I had quite large variations on the delta v and decided that I would rebuild the pack as a 16s3p.  I had extra BMS's so why not.  

After rebuilding the pack and installing the two new BMS I wired all three packs into a common positive and negative bussbar and allowed the SCC and the BMS to do their own thing.  now no matter what setting i put into the charge controller I cannot get the pack to charge any higher than 3.325 per cell (53.2 pack volatge) which is about 80% depending upon whom you talk with, and whose chart you are looking at.  Prior to this it would take the pack to 54.4 and the BMS would eventually limit charge by shutting off the charge MOSFET causing the voltage to rise and fall (which was the issue with my high voltage disconnects on the inverter).  

The fact that it no longer charges above this is a godsend in one way and a dilemma in another.  Why is it suddenly restricting charge to this when it never did it with 1 BMS over the same 32/48 cells?  the numbers are all good, delta v is reasonable for cells that are used/old stock (regardless of what the seller says.) and in the 16s3p config runners are not an issue as much as it was with the 3p16s config.  

so what changed?  the setting in the SCC are the same.  I played with them back and forth over new years in an attempt to figure out what the issue was and no matter how I set the SCC's it ended up the same 53.2 with occasional rise to 53.3.  charging just drops off.  the amps form the SCC ramp down as if it was/were a function of the charge controller but there is no reason fo this to happen.  the BMS's are not shutting their charge MOSFETS off and the inverter is simply drawing excess from the panels to power the load without taking anything from the battery (confirmed with the Magnum BMM shunt, the BMS readings, and a Unit T DC clamp style ammeter.

any thoughts?

Ken

bfitzgerald

To be clear, I am still old school FLA (until they die). This may be simplistic but what is the cut-off charge amps setting on your SCC's? I think you have a 600 ah battery and if it was FLA, I'd start with charge cut-off 18 amps and adjust from there to get the SOC I want.  Probably no help....good luck.

papab

Is it the SCC or BMS cutting out?   Could you have some high, unbalanced cells so the BMS is cutting off?