Top balancing 280ah REPT cells is one cell bad?

musashi1707

Solar Enthusiast
So I top balanced a group of 16 280ah REPT cells from Starmax to about 3.62v. Left them connected in parallel for a couple days after charging.

After balancing the voltages have settled down to the 3.46 range, and are all very very close, 3.461-3.469 except one!

One cell is reading 3.37x and has been steadily falling. What's the deal is this cell bad? I have not yet tested internal resistance.

Thanks.
 

MisterSandals

Participation Medalist
So not yet. but doesn't that massive difference in voltage indicate something.. bad?
If it is behaving significantly different than the other 15 cells, i'd say thats a bad sign.

Can you charge that one cell back up again and see if it behaves the same. Maybe it didn't have the best connection or ?? the first time. I dunno.
 

musashi1707

Solar Enthusiast
If it is behaving significantly different than the other 15 cells, i'd say thats a bad sign.

Can you charge that one cell back up again and see if it behaves the same. Maybe it didn't have the best connection or ?? the first time. I dunno.
Can you perform capacity test on that cell to see what you will get?
So I charged it back up, and it did indeed behave the same. I have received the bms but haven't added that cell to pack yet. I have the capacity tester Will recommends coming in tonight so I should be able to test that one cell by itself. I have to say now that I've built my first pack (yay), these REPT cells from Shenzen Starmax are looking really good so far.

Something noteworthy is that the problem cell dropped down to 3.39 volts steady, and that appears to be a hard wall for the rest of these cells. It looks like about 5ah from 3.65 to 3.32.. I'm now thinking that this means this problem cell is likely still good for 275ah, which is fine with me, provided it balances ok.

I just charged the cell up a third time and to get from 3.39 to 3.65v took about 30 minutes at 4 amps starting, so again very very little power in that voltage range (both for this cell and apparently REPT cells in general).

Attached is a picture of my first battery build with attached 150 amp JBD BMS. Held together with duct tape and zip ties ;-)

Thanks in advance for any pointers.
 

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Bud Martin

Photon Sorcerer
I am really happy with my REPT 280A from ELXIPORC so far. The price has now gone up from $85 to $112.
My test comes out to be 290Ah.
 

Shawn Hayes

Learning Everyday
I am really happy with my REPT 280A from ELXIPORC so far. The price has now gone up from $85 to $112.
My test comes out to be 290Ah.
I just received my cells from Exliporc, still currently opening them (over halfway to 68) but was curious if or how many of your cells seem to be more swollen than others? Just curious if this what others have been seeing?
 

shadowsteve

Solar Enthusiast
I just received my cells from Exliporc, still currently opening them (over halfway to 68) but was curious if or how many of your cells seem to be more swollen than others? Just curious if this what others have been seeing?
I ordered 8 and have received 6 so far. The other 2 should be here Friday I expect. So far completely flat with no damage at all. I haven't done any charging on them but all are at 3.275v
 

Berseker

Solar Enthusiast
I am really happy with my REPT 280A from ELXIPORC so far. The price has now gone up from $85 to $112.
My test comes out to be 290Ah.
At what rate did you test. 1C or 0.2C?
 

musashi1707

Solar Enthusiast
At what rate did you test. 1C or 0.2C?
I see you're asking him but personally I discharged using the tester with the fan/heatsink on it, at.. 17 amps if i remember correctly? So that would be under .1C on the 280, i think (new to all this). My test on the potentially bad cell came out to over 280 amp hours. I think I stopped the test at 282ah and it was 2.9x volts under load, still had juice in it.
 
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