Not hitting 54.6 ?

[Low]

Hi all, after building my 13s 11p pack from re-claimed laptop randoms im struggling to charge it to maximum voltage.
It hits 53.6 and goes green light, i spliced into the charger i got with the ebike and know that at green light on the original factory battery i have 54.6.

So is this simply warn cells or an over safe bms issue and does it really matter? When i built the pack i painstakingly bottom ballanced and got each cell to 3.5 and then made sure it held it for two weeks, do you think a few cycles with the charger left on will help the bms along and get me a higher green light voltage or should i just stop worrying about the lost 9 odd percent and be happy i only spent £83 on all 143 cells.

Tested in and out of the charger, anything else i can do?

Thanks everyone

 

[anotherkiwi]

Worn cells. Individually the cells will charge to 3.5 but because of different internal resistances the weaker ones will drag the others down.

 

[D8ve]

Do some charger,bms systems hit green then balance cells? Have you checked the individual values now?

 

[Deleted member 4366]

Worn cells. Individually the cells will charge to 3.5 but because of different internal resistances the weaker ones will drag the others down.

?????????

The problem is most likely a lack of balance because the cells are different in the different groups. The BMS will switch off charging when the first cell-group reaches 4.25v. If that group has less capacity than one or more of the others,it will reach 4.25v before the others, so the others will be at a slightly lower voltage. You can check that with a voltmeter on the balance wires.

Ideally, when making a battery out of reclaimed cells, you need to check the capacity of each cell-group to make sure that they are equal.

The battery is still useable, but might need some manual balancing from time to time.

 

[anotherkiwi]

?????????

The problem is most likely a lack of balance because the cells are different in the different groups. The BMS will switch off charging when the first cell-group reaches 4.25v. If that group has less capacity than one or more of the others,it will reach 4.25v before the others, so the others will be at a slightly lower voltage. You can check that with a voltmeter on the balance wires.

Ideally, when making a battery out of reclaimed cells, you need to check the capacity of each cell-group to make sure that they are equal.

The battery is still useable, but might need some manual balancing from time to time.

I was trying to explain (badly) what you have said. Individual cells will charge to the same voltage. Groups of cells will not charge to the same voltage if one or some cells in the group have different internal resistance.

Read on battery university IIRC.

 

[Low]

Thankyou guys... Iv been doing 500 meters on her then charging again and seem to be closer to 54.0 now, i can live with that i think.

Did try to group well but that was pre amatur hour with soldering and battery spot welding

Thank you both for your great help during this build.. I owe the forum and will repay.

Will try testing from the bms terminals, didnt think of that, then settle back and call this one a done deal... New cells for the next one me thinks so fewer variables!

Thanks a mil folks.

 

[Low]

Also.. I think my wife may have moved out several weeks ago, is that normal?

 

[D8ve]

Also.. I think my wife may have moved out several weeks ago, is that normal?

That's a bonus that is