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280Ah cells with low capacity - can I still use them?

MattR

MattR

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Joined
Nov 26, 2020
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17
I have 8 280Ah rated LifePO4 that I have tested and have the following capacities:
  • 242.7 Ah
  • 240.9 Ah
  • 244.2 Ah
  • 239.8 Ah
  • 237.2 Ah
  • 241.1 Ah
  • 246.0 Ah
  • 240.5 Ah
Clearly the capacity of these cells don't live up to the advertised specs. I originally bought them to use in my RV with a 3000Wh inverter, but was unhappy with the capacities, so I bought some higher quality 280Ah cells that have performed wonderfully. I think when I used the lower capacity cells that they might have been out of balance which caused the BMS to shutdown. I'm wondering what I should do with these cells. Can I buy another Victron Multiplus and use these cells to power the second 50A leg of my RV? Can I combine the 2 8S packs in parallel to form a 8S2P pack? Any other ideas?
 
ScrotusGobbleBottom said:
You still have 85% usable. This is interesting. Did the arrive like this? How old are they?
Click to expand...
They are probably 3-4 years old now and have been sitting on a shelf for most of that time. I only recently got a tester to see what the actual capacities were. Now that I know there's still a fair amount left, I'm trying to figure out what to do with them.
 
MattR said:
They are probably 3-4 years old now and have been sitting on a shelf for most of that time. I only recently got a tester to see what the actual capacities were. Now that I know there's still a fair amount left, I'm trying to figure out what to do with them.
Click to expand...
Just make a 24v nominal 240AH battery.
Should work fine.
 
Ultimately what your question is is can you have two packs that are different capacities in parallel I think right?

If I'm understanding the question correctly then yes you absolutely can I have one pack that is 1,300 amp hours and another that is 460 amp hours... They're in parallel and they play pretty nice
 
MattR said:
They are probably 3-4 years old now and have been sitting on a shelf for most of that time. I only recently got a tester to see what the actual capacities were. Now that I know there's still a fair amount left, I'm trying to figure out what to do with them.
Click to expand...
If that is the case, I would cycle test them at least 3-4 times from 3.65 down to 2.5 and back before comming to conclusions.
What tester did you use ?
 
ericfx1984 said:
Ultimately what your question is is can you have two packs that are different capacities in parallel I think right?

If I'm understanding the question correctly then yes you absolutely can I have one pack that is 1,300 amp hours and another that is 460 amp hours... They're in parallel and they play pretty nice
Click to expand...
Yes, that's a good summary of my question. Thanks for confirming that.

For the BMS, I currently have a 8S 200A. Can I get another 8S BMS for the second pack? Or do I need to combine the cells in 2P8S configuration with a single BMS?
 
houseofancients said:
If that is the case, I would cycle test them at least 3-4 times from 3.65 down to 2.5 and back before comming to conclusions.
What tester did you use ?
Click to expand...
Okay, would you expect them to be better or worse after several cycles? I used a EBC-A40L
 
MattR said:
Okay, would you expect them to be better or worse after several cycles? I used a EBC-A40L
Click to expand...
Probably better..
They sat for quite a long time, and while in general lifepo4 doesn't have a memory, they may need a warm after sitting for such a long time
 
MattR said:
Yes, that's a good summary of my question. Thanks for confirming that.

For the BMS, I currently have a 8S 200A. Can I get another 8S BMS for the second pack? Or do I need to combine the cells in 2P8S configuration with a single BMS?
Click to expand...
I would set them up as two separate batteries with two separate BMSs... The big advantage to that is that if one of them goes down you can still use your equipment... But you also have twice the available current on tap at any given time
 
Okay, here's what I've learned.
  • Combining multi packs with different capacities in parallel is possible and should work well.
  • I should have one BMS for each parallel pack, which is 2 total for my situation.
  • LifePO4 batteries can temporarily lose capacity after sitting on the shelf for a few years.
Is that consistent with everything that's been communicated here?

Thank you very much, everyone, for your help!
 
MattR said:
Is that consistent with everything that's been communicated here?
Click to expand...
I support all the conclusions presented.

One BMS for each group is absolutely ideal, but I wouldnt consider it mandatory. It would be tremendous insight into how the orphan pack is doing, spot trouble much easier (abnormal cell deviation would be masked if 2 in parallel) , and allow twice the current capability.
MattR said:
LifePO4 batteries can temporarily lose capacity after sitting on the shelf for a few years.
Click to expand...
The electrolite may need some cycling. This is a theory so far in my opinion. Make sure and let us know :)

Combining the same number series packs of any similar-ish capacity is agreed to be fine. Same voltage of course.
 
The lower capacity seems too consistent among that many cells. The highest is 246.0 and the lowest is 237.2. That’s a 8.8 Ah spread and the other six cells are in there. So they only differ by just a little over 3% assuming 280 Ah cells. One or two cells, yeah…maybe. But all eight, too close to be coincidental. I’m suspicious of either the accuracy of your load testing equipment or the process used to measure them.
 
MattR said:
I've started the process of retesting the capacities now. I'll post back in a few days when that is done.
Click to expand...
Just a quick and kinda dumb question, can you measure the size of the cells? Length, height and width? Just in case if you really bought the 280ah model. There were cases where people got scammed into paying for 280ah cell and gotten 240ah cell instead........
 
AshleyL said:
Just a quick and kinda dumb question, can you measure the size of the cells? Length, height and width? Just in case if you really bought the 280ah model. There were cases where people got scammed into paying for 280ah cell and gotten 240ah cell instead........
Click to expand...
Interesting. I've actually bought quite a few of these batteries, and I'm almost certain that they are the same size. When I bought the new cells, they fit perfectly into the tight enclosure I built for these original cells. Now, that doesn't mean the new (good) cells aren't also smaller than they should be. I also haven't tested the new cells to ensure they have full capacity since they are in a location that is difficult to access.

Regardless of all of that, I'll check the measurements and post back here later.
 
Brett V said:
The lower capacity seems too consistent among that many cells. The highest is 246.0 and the lowest is 237.2. That’s a 8.8 Ah spread and the other six cells are in there. So they only differ by just a little over 3% assuming 280 Ah cells. One or two cells, yeah…maybe. But all eight, too close to be coincidental. I’m suspicious of either the accuracy of your load testing equipment or the process used to measure them.
Click to expand...
Fair enough. Here's the testing process. I used a EBC-A40L, which could be absolute junk, I need to confirm the amperage with a meter. I fully charged the batteries at 40A to 3.65V until the amps went down to 1A. After that, I waited for 30 minutes and then discharged at 40A to 2.5V. Following that I charged the cells back to 3.3V at 40A.

These cells were very cheap straight off of Alibaba, so I'm not really too surprised that they have a lower capacity. I would guess that they are either used cells or lower grade that didn't make the original cut. The seller might have intentionally paired up cells with similar capacities to hide it better.
 
MattR said:
Fair enough. Here's the testing process. I used a EBC-A40L, which could be absolute junk, I need to confirm the amperage with a meter. I fully charged the batteries at 40A to 3.65V until the amps went down to 1A. After that, I waited for 30 minutes and then discharged at 40A to 2.5V. Following that I charged the cells back to 3.3V at 40A.

These cells were very cheap straight off of Alibaba, so I'm not really too surprised that they have a lower capacity. I would guess that they are either used cells or lower grade that didn't make the original cut. The seller might have intentionally paired up cells with similar capacities to hide it better.
Click to expand...
unless your EBC-A40L is broken ( which it doesnt look like ) , it is either your method, or the cells...

could be cycled before you got them
could need a little "pep up"

fortunatly it is quite easy to create a test plan with the EBL software to repeat a test 2 -3 times
 
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