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?

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

YuvalS wrote:

djozz wrote:

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.  

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

YuvalS wrote:

Doesn't the charger protect against it?

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

slmjim wrote:

What was the charge rate?

 

slmjim

YuvalS wrote:

will34 wrote:

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

Doesn’t the charger protect against it?

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

YuvalS wrote:

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

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…….

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.

Kame Sennin wrote:

YuvalS wrote:

Doesn’t the charger protect against it?

 

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

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.
https://youtu.be/atkgUwGHL_k

CNCman wrote:

Kame Sennin wrote:

YuvalS wrote:

Doesn’t the charger protect against it?

 

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.

. Im sold !! Thanks I will spring for one for safety

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.

Kame Sennin wrote:

YuvalS wrote:

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

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.

The Miboxer C4-12 also has thermal sensor, similar to the MC3000, although the temperature threshold is not user-configurable, and I think set to a fairly high temperature (55 or maybe 65 degrees Celsius?).

Also, the C4-12 appears to use its IR measurement (again IR measurement cannot be completely accurate due to the contact/rails though) for determining the automatic charge current. And it can use very high charge current for cells that it measured low IR (and conversely, many button-top cells will have high-IR due to the contact point, even if they should have lower IR than measured).

The Xtar VC4S also uses IR measurement to determine the charge current (it tries to charge new AAA NiMh at very high charge current though…). So using IR measurement for the unit to auto-select charge current may not be foolproof..

MC3000 has user-configurable temperature threshold so it may come in more useful (also, if attached to a computer or phone for graphing, one can monitor the temperature raise in the graph, eg. if it’s rising too quickly, may indicate a problem with the cell…)

But, I usually won’t immediately test the capacity of a cell that has unknown condition (eg. 2nd-hand from battery pack) since they could have very high IR, or drained to too low voltage, or other damage. Usually when trying to charge something unknown, I use the slowest charge current (eg. around 100mA) and see if the voltage rises. (after checking that the voltage is not “too low” and also checking the IR first with a battery resistance tester.)

Hey, I just spotted this thread. Yes the BT-C3100 has temperature sensors, but the software ignores them during the charge cycle. At least that’s what I observed.

I“ve been asking after ( in another so far unanswered thread) recommendations for a low power solar charger controller, having accumulated some 5 and 7 AH cells from UPSes. I noticed while searching that almost all of the charge controllers for sale except the very cheapest incorporate a temperature sensor on a cable, meant to monitor the battery and warn against or shut off charging if the battery gets too hot.

It was news to me that some 18650-size chargers have heat sensors. I appreciate the info in this thread — it’s now a feature I know to look for.

Of course, a test result showing that the heat sensors work would be even more welcome. Has HKJ mentioned this feature anywhere?

GOOD LESSON. I had two older hot Tenergy AAAs I was trying to charge yesterday. Had to take them out and discard them. They got real hot to the touch.

hank wrote:

I“ve been asking after ( in another so far unanswered thread) recommendations for a low power solar charger controller, having accumulated some 5 and 7 AH cells from UPSes. I noticed while searching that almost all of the charge controllers for sale except the very cheapest incorporate a temperature sensor on a cable, meant to monitor the battery and warn against or shut off charging if the battery gets too hot.

It was news to me that some 18650-size chargers have heat sensors. I appreciate the info in this thread — it’s now a feature I know to look for.

Of course, a test result showing that the heat sensors work would be even more welcome. Has HKJ mentioned this feature anywhere?

I think HKJ’s reviews will mention the thermal sensors in his reviews… (eg. check SkyRC MC3000, Miboxer C4-12, Xtar Overslim)