How to dismantle a spotwelded battery?

[Cuprani]

I'm having some troubles with my current liion battery pack (12S3P).
This pack does not use a BMS for discharge (only for charging).

I recently removed the wrapping en inspected all the nickel strip spotwelds that I could see from the outside. No signs of heat spots or sparks. I've tested resistance and balance of every pack, and they are all just about the same. So I wrapped it up again. Somehow occasional I have strange voltage drops under high load. About once every three runs.

Here's an examaple of a recent log when the controller registered 4 errors in one run.
http://metr.at/r/Mmxur

It looks like the datalog can't keep up with the actual numbers as there are errors of over current while the current in the log is still very low. But I did register some under voltage situations and confirmed on my build in voltage meter that the voltage of the complete battery was indeed below 30V for a while. I assume there is something wrong with some connections.

Yesterday I fried my BMS while I was charging this battery.
My BMS is end of life now, but I still don't know what caused it. It was already charged for 80% so something went wrong while balancing the battery. I measured all the packs again and the voltage of all packs are within a 0,1V range. I decided I won't use this battery anymore, but the cells are as good as new so I want to rebuild it with an Vruzend or Am Tech kit.

What is the best way to remove the spot welded nickel strips from the 18650 cells?
I saw some youtube video's where the nickel strip was peeled of, but that leaves pieces of nickel strip on the cells.

Could I just sand or grind these of the battery, or will this cause the battery to corrode?

 

[Taswegian]

Wouldn't it be much less trouble to just replace the BMS and see how that goes? Is there a reason you want to change to a no-weld assembly, maybe changing pack shape?

Regarding grinding weld dags - corrosion isn't a concern but heat might be, don't be too heavy handed.

 

[krlenjuska]

When you remove old nickel strip - be carefull not to bend out battery negative side. I always use this to clean old nickel.

 

[fechter]

It's not really easy to remove the nickel depending on how good the welds are. I uses a needlenose pliers to peel up the strips in sort of a rolling action. It's easy to short the pack doing this kind of work, so use tape or cardboard to insulate parts you aren't working on. Once you peel the nickel off, you're left with little chunks of nickel stuck to the end of the cell. The grinding tool like krlenjuska shows is hard to beat but be careful not to take off too much.

 

[Cuprani]

Wouldn't it be much less trouble to just replace the BMS and see how that goes? Is there a reason you want to change to a no-weld assembly, maybe changing pack shape?

Regarding grinding weld dags - corrosion isn't a concern but heat might be, don't be too heavy handed.

I think the BMS has fried due to the battery. The intermitted voltage drops under load indicate there is something wrong inside the battery. I'm afraid I will fry a new BMS when I connect it.

I used this liion in my skateboard, but I think I will go back to lipo's for my skateboard and use these 18650 cells in my new to build ebike battery.

 

[spinningmagnets]

There might not be enough series connections, and that is a frequent source of voltage drop under load.

 

[flippy]

get this plier:

https://www.wiha.com/int/en/tools/pliers/diagonal-cutters/wiha-electronic/100/diagonal-cutters-electronic?c=27

get 2. one to destroy on batteries and the other for fine work.

not cheap but they are really good for stripping nickel from packs.

 

[Taswegian]

Ordered :thumb:

Damn, price history on Amazon shows they were €16 a few days ago.

Not that pricey when you compare to GodHands

https://www.amazon.de/Gott-hand-spn120-Ultimate-Nipper/dp/B008S51O22/ref=sr_1_1?keywords=GodHand&qid=1554990390&s=gateway&sr=8-1

:lol:

 

[flippy]

Ordered :thumb:

Damn, price history on Amazon shows they were €16 a few days ago.

Not that pricey when you compare to GodHands

https://www.amazon.de/Gott-hand-spn120-Ultimate-Nipper/dp/B008S51O22/ref=sr_1_1?keywords=GodHand&qid=1554990390&s=gateway&sr=8-1

:lol:

you can get the wiha for 12 euro at hornbach. :wink:

for stripping packs you put the wrong force in the handle wich makes the grip come loos over time.
in case the silicone slides off the handle you can use acetate glue on the handle and just slide it back. it will never come off again.

use a dremel with the blue grinder wheel to take the weld pits off.

 

[Taswegian]

There might not be enough series connections, and that is a frequent source of voltage drop under load.

The graph shows lots of little sags of a few volts that seems load related but one of the big 'box canyon' drops to 10V is with no load at all.

Surely a bad connection? But not necessarily in the battery itself?

 

[Taswegian]

Ordered :thumb:

Damn, price history on Amazon shows they were €16 a few days ago.

Not that pricey when you compare to GodHands

https://www.amazon.de/Gott-hand-spn120-Ultimate-Nipper/dp/B008S51O22/ref=sr_1_1?keywords=GodHand&qid=1554990390&s=gateway&sr=8-1

:lol:

you can get the wiha for 12 euro at hornbach. :wink:

for stripping packs you put the wrong force in the handle wich makes the grip come loos over time.
in case the silicone slides off the handle you can use acetate glue on the handle and just slide it back. it will never come off again.

use a dremel with the blue grinder wheel to take the weld pits off.

I might have misunderstood, I figure you are cutting under the strip to shear through the welds laterally rather than pulling / rolling the strip (which pulls up/across and is more likely to distort the cell and leave bits torn out of the strip behind)

Seems that would be the normal closing force on the grip, did I get that wrong?

 

[john61ct]

How about a not too-thick cold chisel and small ball-peen?

Drop of oil, keep it sharp

https://www.popularmechanics.com/home/how-to/a10915/diy-skill-of-the-day-using-a-cold-chisel-17021541/

Then polish off the nuggets with the Dremel

 

[flippy]

Ordered :thumb:
Damn, price history on Amazon shows they were €16 a few days ago.
Not that pricey when you compare to GodHands
https://www.amazon.de/Gott-hand-spn120-Ultimate-Nipper/dp/B008S51O22/ref=sr_1_1?keywords=GodHand&qid=1554990390&s=gateway&sr=8-1 :lol:

you can get the wiha for 12 euro at hornbach. :wink:
for stripping packs you put the wrong force in the handle wich makes the grip come loos over time.
in case the silicone slides off the handle you can use acetate glue on the handle and just slide it back. it will never come off again.
use a dremel with the blue grinder wheel to take the weld pits off.

I might have misunderstood, I figure you are cutting under the strip to shear through the welds laterally rather than pulling / rolling the strip (which pulls up/across and is more likely to distort the cell and leave bits torn out of the strip behind)
Seems that would be the normal closing force on the grip, did I get that wrong?

you have to slide the tip onder the strip, that is a bit finniky. the thick handle helps in getting enough foce to do that but ater a while (hundreds) of welds) it might loosen up.

 

[Cuprani]

There might not be enough series connections, and that is a frequent source of voltage drop under load.

The graph shows lots of little sags of a few volts that seems load related but one of the big 'box canyon' drops to 10V is with no load at all.

Surely a bad connection? But not necessarily in the battery itself?

Your right. I see some voltage drops without any load.
Good point. I will check other connections in my board as well. The strange thing is that these problems did not occur with my lipo's. I changed the Li-ion battery for my lipo's right after these problems and tested with no issues.

And then it still doesn't make any sense why my BMS fried..
..but maybe the BMS was another problem on itself and has nothing to do with the other problems..

How about a not too-thick cold chisel and small ball-peen?

Drop of oil, keep it sharp

https://www.popularmechanics.com/home/how-to/a10915/diy-skill-of-the-day-using-a-cold-chisel-17021541/

Then polish off the nuggets with the Dremel

It could work, but i could also damage the surface of the battery. I think peeling it of is a better way.
And I just wanted to know if it is safe to grind the left pieces of.

As most think that is no problem I think I will use my dremel with this in a drill stand, combined with a firm adapter for the cells.

But before I do I will first look into the other connections of my board to make sure the problem isn't in my board instead of the battery.

 

[flippy]

use compressed air to blow any metal left from the dremel out the top. some stuff usually gets under the insulation edge.

 

[sharinginfos]

When you remove old nickel strip - be carefull not to bend out battery negative side. I always use this to clean old nickel.

hi what is the name of that thing?
what is it made of ?

could you provide a link of where to purchase it ?

would greatly apreciate it!

 

[From-A-To-B]

When you remove old nickel strip - be carefull not to bend out battery negative side. I always use this to clean old nickel.

hi what is the name of that thing?
what is it made of ?

could you provide a link of where to purchase it ?

would greatly apreciate it!

It's a grinding bit for a Dremel tool. You can find them at most any hardware store or online -- you can buy multi-bit kits or stock up on just one attachment.

https://www.ebay.com/itm/1842028084...nYiZ9mu1szFF36m1M%3D|ampid:PL_CLK|clp:2047675

 

[sharinginfos]

thanks

 

[docw009]

I buy those diagonal cutters at the local discount big box hardware store for $3 each. Unlike good tools, they wear out quick but I bet the $15 models are the same.
.
I'm getting away from dismantling batteries, but when I was grinding the nickel spikes off salvaged cells, I found they rusted very easily later. Now I try to make them as small as possible w/o a grinder. The ,10mm nickel easily conforms around raised edges when spot welded. A second layer seems to attach OK.

 

[harrisonpatm]

I buy those diagonal cutters at the local discount big box hardware store for $3 each. Unlike good tools, they wear out quick but I bet the $15 models are the same.
.
I'm getting away from dismantling batteries, but when I was grinding the nickel spikes off salvaged cells, I found they rusted very easily later. Now I try to make them as small as possible w/o a grinder. The ,10mm nickel easily conforms around raised edges when spot welded. A second layer seems to attach OK.

Yeah, when you grind the top, you're grinding off the surface nickel on the batteries that's supposed to protect the casing from rust and corrosion. If you know your battery is going to be well sealed in the final build and not at all exposed to elements, you might be able to get away with it. Maybe. In something like an ebike battery, running around outside, I would expect rust to occur in a few months.