Detecting bad cells…

[FatDaddyG]

Hello…
Been racking my brain trying to figure out what’s going on with a couple of 12v Lifepo4 batteries. I made these “Will Prouse” style using 4 CA-100 cells and a JBD 4S BMS on each. 4 of them have been perfect and the individual cells stay within like 1/100 volt. 2 of them have been nothing but problems. They won’t stay balanced and now the BMS is showing one cell that basically appears dead. Here’s what I’ve done…

1. Put all cells in parallel and charged at 3.65 volts for 3 days. Cells took about 5 amps at first and finally dropped to .007A when I finally turned off the charger
2. Put all cells in series and hooked up a brand new, out of the box, just certified Overkill Solar (JBD 4S) BMS.


Got this…


I’m thinking this shows cell #2 as ”bad”?? When I test each cell individually I’m getting 3.2ish volts on all. WTF am I doing wrong?

THANKS!!

 

[Alex1]

Did you measure volatage on balance leads terminals on bms? or just on battery terminals? you didnt connect -B terminal on bms with battery B0 terminal.
I have jk bms and it doesnt work at all if i dont connect -B with B0 terminal on battery, maybe this is the case here?

 

[FatDaddyG]

Hello…
Been racking my brain trying to figure out what’s going on with a couple of 12v Lifepo4 batteries. I made these “Will Prouse” style using 4 CA-100 cells and a JBD 4S BMS on each. 4 of them have been perfect and the individual cells stay within like 1/100 volt. 2 of them have been nothing but problems. They won’t stay balanced and now the BMS is showing one cell that basically appears dead. Here’s what I’ve done…

1. Put all cells in parallel and charged at 3.65 volts for 3 days. Cells took about 5 amps at first and finally dropped to .007A when I finally turned off the charger
2. Put all cells in series and hooked up a brand new, out of the box, just certified Overkill Solar (JBD 4S) BMS.
View attachment 128721

Got this…
View attachment 128719

I’m thinking this shows cell #2 as ”bad”?? When I test each cell individually I’m getting 3.2ish volts on all. WTF am I doing wrong?

THANKS!!

Just scrambled the cells from (141,142,143,144) to (143,144,141,142) and got this…


Thinking cell 142 is bad. Not sure how to confirm but am top balancing the other battery now and will swap out 142 when done in like 3 days…

 

[FatDaddyG]

Did you measure volatage on balance leads terminals on bms? or just on battery terminals? you didnt connect -B terminal on bms with battery B0 terminal.
I have jk bms and it doesnt work at all if i dont connect -B with B0 terminal on battery, maybe this is the case here?

I didn’t think it would matter on the voltage spot but will check again. I didn’t realize you needed anything on the B terminals… trying that too. Thanks!

 

[Alex1]

Unplug ballance ledas connector from bms, connect B- to BC0 battery terminal and then connect battery leads connector into bms.
Look video

,

 

[FatDaddyG]

Unplug ballance ledas connector from bms, connect B- to BC0 battery terminal and then connect battery leads connector into bms.
Look video

,

Thanks… didn’t realize the BMS used the battery - as a ground (assumed that was what the little black wire in the balance lead was for). Didn’t solve the problem but definitely changed the screen.

 

[FatDaddyG]

I didn’t think it would matter on the voltage spot but will check again. I didn’t realize you needed anything on the B terminals… trying that too. Thanks!

Oh, this makes more sense after watching the video. I’ll test the balance leads and see if there is any voltage loss.

 

[FatDaddyG]

Balance leads are all good… the second set of cells reached full charge this morning and looked great In 12v configuration. Started swapping cells from the bad battery into the good one and to my surprise each of them look fine, although a bit under charged for cells that just came off a top balance. All four cells from the bad battery tested good in the good cells. Put them back in parallel and they are now taking 3 amps @ 3.65 volts… more to come.