What is happening to this cell (jumping up and down)

[CurryKitten]

I got a little 180 2s out to check something and noticed I was getting nothing when I plugged it in (all my lipos go onto storage after they are flown) I plugged it in the charger to check the cell voltage and it beeped and told me "low voltage"

I plugged it into a lipo tester and it told me that cell 2 was on 0.5v...eek, never seen anything that low before, and weird as my lipos all go onto storage charge after I fly them.

I wanted to see what would happen if I put a bit of voltage back in, so put the charger on Nimh mode for a minute, and noticed the voltage instantly jumped to 6.xv - which was weird.  I was starting think I had a dodgy connection somewhere, so put back onto lipo mode and had a look what would happen if I put the lowest possible charge into it.

The result was this -

! No longer available

Very weird jumping up and down.  When I took it off charge 1 minute later, I plugged it back into the lipo tester and every time it cycled around to tell me the cell charge it dropped every time.

Clearly the lipo is toast, and so will be disposed of - but I was interested to know if there was a reason for the voltage jumping back and forth like that, as I suspect it might be useful indication that something very wrong is happening

[tim_h]

Could be a loose connection / bad solder joint onto one of the balance lead wires perhaps? Assuming the balance plug end is ok.

Using a multimeter you could test the resistance between the main negative  wire and the black balance wire, then test from the main positive wire and the last (third on a 2s) balance lead wire. These should both be a very low resistance, much less than 1ohm, and both readings should be about the same.

[Coyote]

Thats normally a bad joint or lead as stated above.

[CurryKitten]

Ok, well worth a closer look, so I (carefully) removed the outer layers to look for dodgy connections.  It seemed to look ok, but not having delved inside a lipo, I'm not exactly sure what it should look like.  I took some pics from 2 different angles





The only thing I noted is that there didn't seem to be a metal tag going to the ground like there was on the red/blue wires - but this could be the normal case.

[Andy Sayle]

Could be a dodgy balance connector.....

[FPVSteve]

Not sure I'd trust it in my house tbh

[CurryKitten]

Me neither Steve - it's sitting in it's own lipo bag waiting to be disposed of now.  I just wanted to check if there was anything obviously wrong in the wiring... the fact that there's nothing obviously wrong makes it all the more dodgier IMO. 

Not sure I'd trust it in my house tbh