Battery pack repair

[cwah]

Hello there,

I committed to help a lady in France to repair her batteries pack. She uses 36V10AH pack and told me her pack only allow her to do about 5km distance before the battery shuts down.

She managed to get few of them from seller warranty and they all have the same issue. She told me the problem for all the pack she have had. I decided to get her pack and examine it for her:

The 2 packs haven't been used since 1 year, and they have been sitting at 25V and 32V.

Aluminium box is easy to remove:

I'm currently charging it so I can do a capacity test. I'm currently wondering if the issue may come from the controller who could also shut down from overheat rather than being a battery issue after 5 km...

 

[Deleted member 4366]

Youhave to take the bottom piece off, turn it sideways and use it to push the contents up the aluminiium box.
Next, you have to cut back the heatshrink to expose the BMS under that yellow fibreglass.

Now you can unplug the multipin connector and measure the individual cell voltages (each adjacent pair). That will tell you what the problem is so that you can repair it.

 

[cwah]

Yes I'll do that!!

The first pack already finished charging at... 38.1V!!! In half an hour!

I'm going to dismantle the pack:

 

[Deleted member 4366]

You only need to work at the top. No need to disassemble everything unless one cell is down to zeroo, which it could be with the pack at 38.1v. You're missing 4.1v, which is one cell!

 

[cwah]

Aaaahhh.. too late:

These are pouch cells:

Going to measure voltage from the top then

 

[cwah]

Ok, I now have access to it:

These cells are massive. This 36V pack weight 4kg. Not sure if it's supposed to be a 10AH pack because I can't find reference anywhere. Anyone knows where that's from?

 

[cwah]

Ok, I've found the 4.1 cell at the bottom of the pack.

There isn't any dead cell. But I have huge voltage range. I have 3.6, 3.7, 3.8, 4 and 4.1V cells...... Maybe the BMS isn't able to balance with so high voltage difference.

I'm going to balance charge them with my 10S icharger to see if it can solve it.

 

[cwah]

hmm.. balance plugs are not JST-XH.... I'll have to re-solder the wires to put the jst-xh from my charger...

 

[cwah]

voltage from celllog:

 

[flecc]

These cells are massive. This 36V pack weight 4kg. Not sure if it's supposed to be a 10AH pack because I can't find reference anywhere. Anyone knows where that's from?

The cells look identical to those eZee used to use in a battery made by Phylion in China. That also weighed 4 kilos and it was a 10Ah battery.

 

[cwah]

Are they any good? They look big, bulky and easy to fail lol

 

[cwah]

I've put all the wires directly to the balance plug lol

This is going to be the longest balance charge I'll ever have....

I have cells from 3.7v to 4.15v.... I'm even wondering if it might be a BMS failure to balance?

 

[wurly]

I had a battery pack with those cells, mine were expanded so i didn't bother trying to recover them. Those cells look in better condition. Maybe you are right the BMS isn't doing it's job properly. Fingers crossed for you

 

[cwah]

do you know the cells name and specification? Currently I don't even know how many AH it's supposed to have...

 

[muckymits]

Cwah is there not a Maplins type shop in France? A plastic box would be soo much better than a old cardboard box, cut to shape by a gerbil.

 

[cwah]

Yes I can find that in but as my cardboard is working fine I thought I could leave it as is.

What is a gerbil? I currently have a Proxxon to cut but it doesn't cut big items or very straight

 

[peerjay56]

Yes I can find that in but as my cardboard is working fine I thought I could leave it as is.

What is a gerbil? I currently have a Proxxon to cut but it doesn't cut big items or very straight

Err...

 

[Deleted member 4366]

It doesn't look good. Nearly every battery I've ever seen with those cells had knackered ones.
Off the charger, you had 38.1v. Later, when you measured with your cellog, they come to 34.5v. That's nearly 4v loss without doing anything. Maybe your cellog doesn't measure properly (or your voltmeter).

The high cell at 4.1v is the one that shuts off charging before the lower ones get a chance, which is what's causing the loss of range. If you re-balance them all, it might help, but I think there's going to be some knackered ones that go out of balance again very quickly You need to test it to see. It might be just a crap BMS that can't balance properly.

 

[cwah]

So even if I repair it, it's very likely going to fail in the future?

I have at home a bunch of zippy compact 9s I could re-wire to 10s and fit perfectly the battery frame:
ZIPPY Compact 4000mAh 9S 25C Lipo Pack (EU warehouse)

But I'm a bit concern to give lipo to someone without knowledge whatsoever on battery. It would however have BMS and be protected by aluminium box.

Can I give her lipo packs to have a cheap and lightweight pack?

 

[Deleted member 4366]

I think you should balance it first, then give it back to her to try. If it goes down on range again, then you need to do something. I can''t think of any reason why yo couldn't use the BMS with lipos. The voltage is the same. I think we can be fairly sure the high voltage control is working, so the worst danger is covered.