Faster way to test single cells?

Shale MacGregor

Solar Enthusiast
I need to capacity test so I can match ~ 400 cells, is there a faster way to do this than limiting it to .2C ? I tried testing at .5C thinking I would adjust "expected" capacity and it would enable me to match cells, unfortunately this caused voltage sag below the 2.5V mark waaay too soon. These cells are rated at 2C and are 60AH.

I use a Siglent Load Tester that can do up to 200 Watts, and I have a shunt that works great using a load with an inverter for real world testing, but that only works for 4s.

I was considering hooking up a large enough array to max out my 1000 watt inverter at .2C ( 7p4S), and when one cell hits the minimum I could stop, give all of the batteries the minimum score (divided by 7) and then by testing voltages break them into more groups, or else just test each one from that point forward.

Is this a good idea, or does someone have a better one that would be advisable. Id rather not buy a bunch of shunts / load testers just to save time but at this rate it will take me a few months.


Thanks!
 

MattiFin

Solar Addict
Discharging 16s pack to weakest cell limit and continuing invidually from there is valid idea. 7p4s pack would be more difficult as you can’t be 100% sure of the current dividing equally between cells/strings.
 
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Shale MacGregor

Solar Enthusiast
Discharging 16s pack to weakest cell limit and continuing invidually from there is valid idea. 7p4s pack would be more difficult as you can’t be 100% sure of the current dividing equally between cells/strings.
Thanks! I've actually come up with a way to quickly add/remove batteries to testing rigs so my only real hurdle is settling on a methodology that is legitimate before burning through a few weeks of work.

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I have an overkill solar 16s BMS, I will top balance each group of 16s at 3.65V using 120A charger, and then discharge at 11A (.2C) which should take around 5 hours, using a 48V Inverter and a ~550 watt load (could i increase this C rating to .5C if I am more worried about cell matching than what the actual rated capacity is? IE, if I discharge at .5C and these cells which could be 55AH give a result of 40AH, I am more worried about which cells fall into the grouping of 38AH, 40AH 42AH, etc).

Otherwise at 5 hours per day, I might get 2 of these tested each day which would be a few weeks just for this step, the comes individually discharging the cells to get the total.
 
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