Just a reminder - do not leave charging batteries unattended!!!

Today while charging some 18650s, I smelled a strange smell.
At first I ignored it, but then i realized it is coming from the charger.
The cell was so hot I couldn't even take it out of the charger and had to use a glove.

After I took it out, I noticed some liquid got out of the cell and it melt the charger




Stay safe!


thanks for sharing.

this looks scary

Yuk, good that you saved the situation!

The usual questions: what type of battery was it? Was it abused before in some way? Do you think it was the charger and not the battery?



It is a CGR18650CG from an electric bike pack.
Maybe I damaged it in some way while tacking the pack apart but there is no noticeable sign of damage on the cell and all the other cells from the same pack I checked were good.
I don't think it is the charger since I used it earlier today without any issue.

Seems like overheating from force charging a battery with high IR?


Doesn't the charger protect against it?

Was this the first time you charged this cell after taking the pack apart?



Yes, Tested the capacity

As far as i know most chargers don't have temperature detection for the batterry.

That's one of the reason that made me choose the expensive MC3000

Usually the chargers that have cell temperature monitoring have a third metal part in between the (+) and (-) connections, that touch the side of the cell case and is internally connected to a temp sensor.

Edit : added picture below

What was the charge rate?

slmjim

It was a capacity test, the Opus does that at 500mA.

I know it does not have a thermometer but it does test IR...

some chargers have individual temperature sensors
(under the battery, not the internal cell type)

others do not, or may have only one for all the cells

wle

So i misunderstood you sorry ... you mean that because the charger can do IR measurement it should use that information to avoid problems ?

I haven't heard about a charger that would do that.

IR measurement is just an information and a pretty inacurate one.

When testing cell from used laptop batteries i have seen some that seemed perfectly ok until they reached about 3.9-4.0V where they started to overheat quickly.

The only safe way is to have a temperature monitoring.

The MC3000 has a programable temperature limit for each cell but it expensive so some people use a cheap external alarm thermometer to monitor their cells when charging them.

I have only taken a couple of packs apart - and I’m not keen on doing it lol. Had a couple of sparks/smoke out of the last one whilst doing it (nicked/tore the wrapper) - freaked me out so much I threw the cell down the garden just in case lol!
It didn’t explode or anything - but I did discard it.
I won’t be doing it again……. :stuck_out_tongue:

It happens, not very often but it doesn’t change the fact.
I would guess you found the one bad cell that usually makes a pack go bad in the first place.
I dont know why it happens, I have heard theorys, but one cell almost always goes bad leaving all the other cells with good life still left in them.
I remember in the Dewalt packs the first cell powered the elctronic protection circuit at all times. So when you ran the battery down and didn’t charge it back up for a month or two the circuit would drain the first battery down to low, then the charger would report a bad pack. Making you a new boat anchor.
In two cell series lights they use to claim that the cell closet to the head would always be the one to catch fire because all the current had to run through it from the tailcap cell.
I seen several post showing that very thing, so that does seem to be true even if the reason why isn’t.
.
To me it does look like excessive heat, usually caused by degradation and high IR. Doesn’t look like it had to much longer until thermal runaway and flames.
So where you running a capacity test on the cell or charging the cell back up after the capacity test? Maybe I missed it but I’m not sure which.

.
Im sold !! Thanks :+1:
I will spring for one for safety :wink:

turn on the charger and measure the melted slot.
compare to the others.
sounds like mosfet shorted and passed unregulated(+5 or +12) through to the cell.

The RC guys have fireoroof bags for charging packs. And back in the day chargers usually came with a temp probe, too. Those guys found out early on how dangerous a pack can be. Damage is much more common than other lithium uses. Won’t help when you have a large charger but the idea is worth a look. I will be building something with at least sensors that remove dc power to my lii-500. Found this guy who did some testing of various ones with cannon fuse lol.

Be aware, temperature monitoring can help protect against an overheating cell, but problems like a severely discharged cell that has developed an internal short can potentially still continue into thermal runaway.

I think it is particularly important when salvaging cells to monitor the charging process closely for the first couple of cycles.

Even with good cells, I don’t like the leave the charging entirely unattended, unless it is on a flame-resistant surface with nothing flammable around. Perhaps this is an over-abundance of caution coming from having known some remote control folks, but it’s a pretty easy precaution.