Repairing Lithium ion battery packs

[fizzy]

Like these.
Got 5 Electric scooters to repair and bomb out - owe us money.
One working pack the rest are not working even though they show voltages of 36v each.
Looked at a few Youtube videos - most of them look fairly easy to check each cell etc but these are a nightmare due to the board position.
Any help most welcome

And no I didn't take the photos vertical - software has rotated them

 

[Pilgrim22]

Wait until they spontaneously combust and then claim on the insurance.

 

[julianf]

I can't see from the photos but I assume the cells are spot welded to bus strips, and then the strips are folded up somewhere and soldered to the PCB?

I guess you would need to desolder the bus bars (strips) from the PCB and go from there?

 

[julianf]

Question: Is it some of the cells at fault or the BMS?

As back up to the above, my Milwaukee M18 battery pack failed.

All the cells were fine. It was the BMS that was the issue. I replaced the PCB with one from AliExpress, and, so far (a number of charge cycles) there have been no issues.

 

[Matchless]

If all 5 are the same you can swop the BMS over to check if that is the issue rather than the cells, they look like the same cells as my SegwayLifepo4 or something similar, you could probably de solder the BMS from the good pack without disturbing the hot glue holding it to the cell pack and then use long wires to attach it to other cell packs, maybe,

 

[fizzy]

Yes, but be aware that the BMS disconnections/connections, to the cells, need to be carried out in the right sequence to avoid damaging it.

How can you tell the right sequence?
And why does each battery pack have it's own charging circuits?
No wonder they are so expensive. The "chargers" sold for battery drills are just adapters really. Such a waste having to buy a charger inside every battery!

 

[carbon]

Such a waste having to buy a charger inside every battery!

I would say this is classed as more of a consumer item and as such has all the necessary charge and discharge protection built in so really anyone can plug it it and not burn the house down, in theory. All of the model batteries I have don’t have any bms’s attached and rely on the user having the correct charger with balance ports and set to the correct battery chemistry to do all of the balancing and battery management.

 

[Jan-DIY]

Looks like 10S3P config.
If they deliver 36V all cells are in working condition.
I assume that the battery management system cuts out. Can you draw significant power from the main connector?

 

[Nomad]

Got 5 Electric scooters to repair and bomb out - owe us money.
One working pack the rest are not working even though they show voltages of 36v each.
Looked at a few Youtube videos - most of them look fairly easy to check each cell etc but these are a nightmare due to the board position.
Any help most welcome

And no I didn't take the photos vertical - software has rotated them

Question : what voltage is written on the charger / battery?
(I've heard of fully charged 36v batteries not working if system settings have been changed - system then thinks you have a flat 42v battery not a charged 36v one, so refuses to turn on, if you have no history with these you can assume nothing,)

Odd, I've worked with a few different 36v E-bike batteries, as long as they showed more than the "low voltage cutout" (LVC) - often about 34v - they worked ok.
Can you get 1 complete scoot working then use that to test parts on the other scoots? (batteries, motors, displays...)

As long as the battery shows more than LVC they should at least turn on the bike display, old / tired / flat batteries might turn off again when you try to ride it but that';s a different problem.
BMS are often connected with a plug-n-play connector (several thin wires), if you can find that you can use your good 36v battery to test all the other BMS's.
Keep us updated, if you have 36V I'd expect things to work

ps - vertical photos work fine, no reason not to use them

 

[fizzy]

Question : what voltage is written on the charger / battery?
(I've heard of fully charged 36v batteries not working if system settings have been changed - system then thinks you have a flat 42v battery not a charged 36v one, so refuses to turn on, if you have no history with these you can assume nothing,)

Odd, I've worked with a few different 36v E-bike batteries, as long as they showed more than the "low voltage cutout" (LVC) - often about 34v - they worked ok.
Can you get 1 complete scoot working then use that to test parts on the other scoots? (batteries, motors, displays...)

As long as the battery shows more than LVC they should at least turn on the bike display, old / tired / flat batteries might turn off again when you try to ride it but that';s a different problem.
BMS are often connected with a plug-n-play connector (several thin wires), if you can find that you can use your good 36v battery to test all the other BMS's.
Keep us updated, if you have 36V I'd expect things to work

ps - vertical photos work fine, no reason not to use them

Vertical photos and videos are the spawn of the devil - except for the Eiffel Tower of course
One of the packs does work and powers all the scooters up - the others not a peep!

 

[fizzy]

Just measured voltages.
Knackered packs are around 36v. One is 34.6. Working pack is 39.9V
Perhaps voltage dropped too low and they now won't allow a charge?

 

[Nomad]

What voltage is written on the charger / motors?
I use 36v E-bikes, batteries when fully charged are about 41.5v and work until they get down to about 32v

A "42v" battery will run until it gets down to about 39v
I suspect your bikes are seeing your batteries as "nearly flat 42V" not "charged 36v" batteries

Another option - one of the groups is cell in the battery has dropped too low so the whole battery will refuse to operate.
To check you need a multimeter on each group of cells, I've been told it is possible to charge the "too low" group of cells using an old mobile phone charger but you need to read up for yourself.

 

[fizzy]

Been in hospital so batteries were off the menu for a while!
Brother has tested and found the following

working battery - 0V on charging connector
3 knackered batteries all read 0.382V on charging connector.
Any further ideas anyone?
What could be causing the back voltage?