What is the appropriate way to get the 18650's out of the hoverboard battery?

[markg85]

Hi,

For reference, see this ebay posting (i'm not advertising!): https://www.ebay.com/itm/36V-4-4Ah-Replacement-Battery-Balance-Wheel-For-Balance-Scooter-Board-2-wheel/323010290967?epid=1941699577&hash=item4b34e9e517:g:EFAAAOSw~gRV4BeZ
It contains 20 18650 cells.

I want the cells out of it. Without the BMS and re-wire them in a different setup (4s5p). Now i'm wondering what the appropriate way is to cleanly unhook everything?
I'm being extremely careful as a short with those cells is something i kinda like to prevent. So what i'm doing is:
1. Clear the wrapping plastic
2. Remove the BMS cable from the BMS board (it becomes visible once the wrapping plastic is removed)
3. Now comes the stuff that scares the shit out of me. It's all live and connected, how do i safely proceed from there on?

What i just did is removing the first + (positive) wire from the cell to the bms, that wire is soldered onto the battery bus bar.
The scary thing that just happened is one bus bar from one battery (spot welded) just easily popped of. Not by intention, just by the gentle touch of trying to cut the soldered wire on the OTHER side of the same bus bar. So i thought: oh well, fine, then i just remove it from there. Then i got sparks from the bus bar that was a moment ago still spot welded onto the battery and was now touching that same battery again (so no short). But that sparking scares the hell out of me as it is a sudden burst of energy from the battery (otherwise you wouldn't have sparks), which cannot possibly be the best way. There must be an easy way to disconnect all of that without sparks flying around?

I'm not fond of desoldering the wires to go from the battery to the bms as those are live as well. Desoldering might work, but that will certainly give sparks as the wire gets freed from the BMS. And that might be even more scary as then you'd have sparks and hot soldering...

Just cutting the wires right after the bms seems fairly safe if one can prevent the cut parts not touching each other again after cutting.

So i'd really like to know if one of you knows of a safe way of getting the individual cells out a spot welded battery pack.

Note: i'm quite surprised that some battery packs (this isn't the first one where i notice it) are this badly spot welded! I mean, it just popped of by very slightly touching it. That - in use - is very dangerous! As that meant it already had a barely connected surface. I don't think i have to tell you folks what can happen is connections are being made, but just barely. Something with sparks, heat and fire


Best regards,
Mark

[TerraHertz]

I think you are being overly nervous. The only hazard to avoid is actually dead-shorting batteries. So just cut or desolder the wires one at a time. I'd disconnect the leveling (mid-battery-string) wires first, then the battery string end wires, then separate the individual batteries from the string.

The total voltage can't be more than 4V x number of batteries. Since the entire battery pack is electrically floating (not connected to anything else) you can safely use a soldering iron on any one node at a time.

It sucks that a spot-welded tab broke off. Cheap manufacture.
FWIW, I've found it easy enough to solder wires to the metal can ends. Clean with fine sandpaper, used flux-cored solder, and an iron with plenty of power and a big flat-end tip. Solder quickly, cool off battery with a damp sponge immediately after. Didn't seem to have any bad effect on the cell. Probably best to do this with cells that are discharged to near empty.

[NiHaoMike]

FWIW, I've found it easy enough to solder wires to the metal can ends. Clean with fine sandpaper, used flux-cored solder, and an iron with plenty of power and a big flat-end tip. Solder quickly, cool off battery with a damp sponge immediately after. Didn't seem to have any bad effect on the cell. Probably best to do this with cells that are discharged to near empty.

Watch Rinoa Super-Genius if you want a "how to" video of soldering directly to lithium batteries. She uses a huge soldering iron designed for sheet metal work, but a quality soldering gun works as well and is much easier to find nowadays. (I use a Weller D550 - a bit of an investment but well worth it if you often solder big stuff. The first pack I assembled with it is a huge 12.8V, 82Ah LiFePO4 pack!)