Replacing a single 280ah cell—Where to purchase

[Sipma02]

Hello all,

I'm wondering where to purchase a single 280ah Lifepo4 cell.

After about 30-50 cycles, I think one of my cells is bad. It's also consistently lower voltage (around 150-200mv) than the other ones. My Chargery BMS8T is reading the internal resistance as 13.5, with the other cells being 1.1, 0.4, and 0.4.


So to my best guess, cell #4 is bad (or at least severely mismatched). Does this seem accurate? What are my options? This install is in our Sprinter van—in which we live full time and need to use the batteries for charging, work, fans, fridge, diesel heater fan. I have limited access to... stuff. Here's what I think my options are:

1) Heltec active balancer as a bandaid/temp fix https://www.amazon.com/Heltec-Equal...08CKPZ7PH/ref=cm_cr_arp_d_pl_foot_top?ie=UTF8

2) Top balance? as a bandaid/temp fix. I don't have a adjustable power supply with me, so I'd have to buy one...

3) Get a new cell to replace #4.

My main question is where in the world do I get a single 280ah cell? Are there any US resellers, or anyone here on the forum want to sell me one? Maybe I can jump in on an order to reduce shipping? Looking at current prices on Alibaba, it would be almost $250 for a single cell. May as just well buy 5 more (for a total of ~$675) and double my system while I'm at it but we were really hoping to not spend that kind of money right now...

Thanks!

 

[DJSmiley]

Did you check at the actual cell terminals?

Bad/loose connections can cause similar issues.

I would try swapping eg #4 with #1 and see if the issue moves to cell #1, confirming it's the actual cell.

 

[Steve_S]

STOP !

That is a whacked number and indicator of something else. Process of elimination and no jumping to conclusions based on assumptions.
- Check teh BMS Wire Harness for continuity, good crimp etc. Disconnect harness from BMS 1st then test each lead to connector end.
- Ensure the terminal face in the cells are "Clean" and in good order.
- Recheck the busbar as well, no Burs or Raised edges which CAN cause erroneous readings. Also ensure they are clean.
IF needed, using 500-1000 grit wet/dry sandpaper will clean off the terminal surfaces & busbar contact surfaces nicely. Then wipe with Rubbing Alcohol.

IF all of that is good and double-checked, the next step would be to charge the ONE cell up to match the rest. The BEST option would be to disassemble the pack, clean everything up & Top Charge & Top Balance the 4 cells and reassemble them. First put an identifier on each cell BEFORE disassembly so you know which cell is which when you reassemble so if that one cell IS bad, you will know it is the same one.

 

[Sipma02]

Just spent the past 45 mins testing, disassembling, and re-tightening. Im embarrassed to admit that the terminals on (you guessed it) cell #4 were loose. The voltage of all cells (measured at the cells w a multimeter) was within about 20mv. While I was in there, I sanded all the cell-level bus bar connections.

Everything seems to be charging (and discharging) fine. Cells are now within about 25-30mv at around 15-20 amps of charge. It's a beautiful sunny day and the sun is filling these cells right up.

@Steve_S and @DJSmiley THANK YOU for the fast response. I dont know why my little brain didnt think to check the easiest stuff first!

 

[JRG]

Glad it was something simple!

 

[Steve_S]

Just spent the past 45 mins testing, disassembling, and re-tightening. Im embarrassed to admit that the terminals on (you guessed it) cell #4 were loose. The voltage of all cells (measured at the cells w a multimeter) was within about 20mv. While I was in there, I sanded all the cell-level bus bar connections.

Everything seems to be charging (and discharging) fine. Cells are now within about 25-30mv at around 15-20 amps of charge. It's a beautiful sunny day and the sun is filling these cells right up.

@Steve_S and @DJSmiley THANK YOU for the fast response. I dont know why my little brain didnt think to check the easiest stuff first!

I am HAPPY it was a simple fix, 90% of the time IT IS but it is something folks do not want to go back and redo for some reason.
Now sit back with a nice cold pop and breath that ever so important sigh of relief.

Happy to have been of assistance.

 

[Luthj]

I had a grain of sand cause high voltage disconnect and balance issues on my pack, so its not an unusual problem!

 

[Sipma02]

I had a grain of sand cause high voltage disconnect and balance issues on my pack, so its not an unusual problem!

That's wild. If that was the case for you, I'm surprised I was able to even get my system up and running reliably for the past month! Hope your travels are going well

 

[Luthj]

Well, I did go 40 cycles without hitting 3.45Vpc. That was with C/2 discharge and C/4 charging intermittently.

 

[jrcleveland1990]

well i destroyed a cell by overcharging so i ordered 4 more incase i have more issues proly take another month but i will have 3 extra from California if anyone has any future problems i can help out when they arrive