1 cell overcurrent charging problem

[Troubles in Travel]

Hi, It's my first post, just build a first battery in my life. BMS did not blow up, app connection is successful, cells 3,33-3,34V.
PROBLEM: when i pluged a charger to battery, cells have different voltage during charging. When I crank up the power supply, to 14v 2A, they are disconnecting due to 1 overcurrent cell protection (3,6V)

Video here:

BMS: JBD-SP04S020
4 cells 280ah

Thanks for any advice

 

[sunshine_eggo]

Your battery is imbalanced. It needs to be top balanced per the guide in Resources

 

[Troubles in Travel]

But the voltage on all cells is the same when not charging.

 

[sunshine_eggo]

But the voltage on all cells is the same when not charging.

Not relevant.

"Balance" refers to state of charge, not voltage. Even horribly imbalanced batteries may show almost identical cell voltages when operating in the flat portion of the LFP curve.

Cell #4 is at or near 100% SoC.

Cells 1-3 are at lower states of charge.

 

[Troubles in Travel]

Thank You, I will top balance, and reconnect, and publish results.

 

[sunshine_eggo]

Thank You, I will top balance, and reconnect, and publish results.

Please please please follow the guide. Read it first from beginning to end. It will save you pain and anguish.

 

[740GLE]

Also use better leads from the PS to the battery.

The free ones (24awg?) should be used for a DMM to read voltage only, not send current.

Not saying those leads are the cause of the issues but the aren’t helping

 

[Hobbydarren]

I have

Also use better leads from the PS to the battery.

The free ones (24awg?) should be used for a DMM to read voltage only, not send current.

Not saying those leads are the cause of the issues but the aren’t helping

I agree. I have a similar power supply and even at 1.5 amps charging on a single cell there was a 0.5 volt drop over the cables that came with the unit. I have since replaced them with higher end banana plugs and 12 gauge wires with ring terminals. I even made the leads as short as possible to keep resistance to a minimum. Can't hurt to be more accurate.

 

[sunshine_eggo]

Also use better leads from the PS to the battery.

The free ones (24awg?) should be used for a DMM to read voltage only, not send current.

Not saying those leads are the cause of the issues but the aren’t helping

Yep. that's why I said to read the guide beginning to end... it discusses the need for better leads and provides guidance.

 

[Troubles in Travel]

I have other leads made for serious work. This one are just for testing, but thanks

 

[740GLE]

Is this the first charge applied to the cells?

Where did you buy the cells from?

How long have you had them before you started charging?

 

[bgflyguy]

I would back down to 13.9v or 13.8v, and make sure you have you "absorption" on the charger set to allow for balancing on the jbd.

The difference in resulting capacity will be almost nothing. And even more so, if you don't have this set up correctly now, even if you do a perfect top balance, it will drift over time.

You don't need to go over 14v for a full charge.

 

[Troubles in Travel]

Is this the first charge applied to the cells?

Where did you buy the cells from?

How long have you had them before you started charging?

I was precharging the cells before battery assembly, but after reaching 3,333v on all cells i thought they are factory balanced and i stoped.

I bought a cells 6 months before from aliexpress from SOONBUY Official Store. They had quite ok reviews (beside some ppl said they got bloated cells) and fair price.

Around 6 months on shelf.

 

[Troubles in Travel]

I would back down to 3.9v or 3.8v, and make sure you have you "absorption" on the charger set to allow for balancing on the jbd.

The difference in resulting capacity will be almost nothing. And even more so, if you don't have this set up correctly now, even if you do a perfect top balance, it will drift over time.

You don't need to go over 14v for a full charge.

I already dismounted battery and decide to make it like i should before.
I connected cells in parallel, set the 3.6v voltage and I'm waiting. For now they are still charging at 7A current.

 

[Troubles in Travel]

Something crazy happened during charging.
I charger whole pack to 3,6V, current dropped to 0,15A. I disassembled the pack, checked the voltage, and on 2 cells, voltage was 3,595V, and on other two voltage was 3,33V. All cells were connected firmly with copper bars.
I have no idea, why there was no transfer of electricity to the other 2 cells. I checked connectivity with a voltmeter and it was okay.
Now im charging only this 2 cells alone.

 

[740GLE]

How long did you wait once the current had fallen so low?

 

[Troubles in Travel]

About 12 hours from 1A to 0,15A

 

[sunshine_eggo]

Something crazy happened during charging.
I charger whole pack to 3,6V, current dropped to 0,15A. I disassembled the pack, checked the voltage, and on 2 cells, voltage was 3,595V, and on other two voltage was 3,33V. All cells were connected firmly with copper bars.
I have no idea, why there was no transfer of electricity to the other 2 cells. I checked connectivity with a voltmeter and it was okay.
Now im charging only this 2 cells alone.

Not all cells behave the same. Those two, as outliers, are a concern. They may have notably higher resistance than the other cells.

Recommend you hit each of the 3.33V cells with the power supply and see how they behave.

 

[Troubles in Travel]

I spend whole day trying to find the cause of the problem.
The problem was connection between diy bussbar and surface of cell. My bussbars are thick and almost don't bend at all. When i made them, i polished them on both sides, to make them flat and without sharp corners, but it seems they need to be 100% flat.
Solution was to polish them on sandpaper laid on super flat surface and screw them a little bit harder.
Now im charging them as whole 4 cells pack.

 

[sunshine_eggo]

Please accept my apologies. Most times I try to include checking the connections as part of my first response. I was too hasty.