How hot is too hot?

When testing your cells, how hot do they have to get before you decide to throw them out?
Seems the thermal runaway temperature is over 300F, but I've pulled a couple at 150F just because it seems too hot to me.
I've been charging and discharging at about 500mA.

If you can't touch them, they are too hot.
However, some cells can get hot on their first charge, let them set for 2 weeks, and charge again and they're fine. I just depends.

We went into pretty deep detail on this in another thread; almost exact same thread name.

Ok. I searched around and didn't find it. Do you have a link?

Hrmm, interesting. I can't find it now There was a thread that ended up being a couple pages long. Not sure where it's at. Plus, you can't search for terms "less than 4 characters in length".

However, this is one that is pretty close.

http://secondlifestorage.com/t-So-what-is-a-Burner-Cell

But essentially, if you can't touch it, it's too hot for a powerwall application. Especially if it gets hot on a second charge/test. At that point, flashlight or binned. Not worth the risk of setting off fireworks.


Update:
I tried to do some more searching, and I can't find it or one similar. That is odd. It might of ended up under a different title.

f im not mistaken the thermal runaway is around or above 120C... BUT.. there have been tests that above 85C over period of time can cause reaction.
This is HOT!

I would personally not use cells that cannot be touched. imagine the heat they produce inside a pack and the amount of energy that cell witll brun into heat instead of storing/used...

Also note that charging at lower current or not as high will on many sanyous not cause any temperature at all.

I have to say I find most of these hot cells to be leakers. Typically when I am doing my initial voltage readings and they are < 1 volt, I throw them in parallel with a good cell just to bump up there voltage. Now I take them out before charging, if the voltage is dropping (leaking), I toss them in the recycle bin no questions asked. I suspect that is I tried to charge them they would be burners.

-Bob

rebelrider.mike said:

When testing your cells, how hot do they have to get before you decide to throw them out?
Seems the thermal runaway temperature is over 300F, but I've pulled a couple at 150F just because it seems too hot to me.
I've been charging and discharging at about 500mA.

Click to expand...

I don't look at the thermometer other than when I'm curious to see how overheated it got. If I put my hand on it and it makes me think "damn that's hot", it's too hot. It seems like that starts for me around 120F, but I guess everyone's hand is different.

Thanks everyone! Seems I'm pretty much doing the same stuff as everyone else. I'll check them by hand every now and then. Most range from stone-cold to warm, subjectively, but the ones that feel hot I'll actually measure.
Some of the hot ones do quite well, but most have very low mAh, or won't fully charge. I've started marking the hot ones and setting them aside to fiddle with later. I find they are actually physically uncomfortable to handle starting at around 125F, and I'll go ahead and pull them at 150F.
I finally have enough good tested cells that I'm not as concerned as I was about keeping every possible cell. I think I'll actually have enough to build the batteries I have in mind.

This one is actually hard to say because it depends on the cells you are using. You should look at the spec sheets of the cells. For instance the LG HG2 specs say the following:

https://www.imrbatteries.com/content/lg_HG2.pdf

2.9 Operating Temperature (Cell Surface Temperature)
Charge 0 ~ 50?
Discharge -20 ~ 75?

2.10 Storage Temperature (for shipping statei)
1 month -20 ~ 60?
3 month -20 ~ 45?
1 year -20 ~ 20?

So 50C for charging and 75C for discharging is too hot, when you keep in mind that you should never run at absolute max. So if you're charging them and they get above 120F (keeping in mind that the room temperature also has a play in this) then it would be wise to discard them.

Yes, if a cell gets to 50C/120F, then it's to be put aside. Most likely recycled. However, it is possible that cell will only reach this temperature when it's at it's 4.1-4.2V charge state. So, it could run cool if it's only charged to 4.05V. But I would not put these cells into a powerwall application. They would be used only for single cell applications (flashlight for example).

Also to note, some cells may reach this temp during initial charge. After they have reached their 4.2V, sat for a few weeks, (assuming no large self-discharge) discharge slightly (around 3.6V) and then recharge, they may very well not heat up again.
I've had a few cells not re-heat on the second charge. I have no idea why that is. But, as I stated, these cells aren't going into the pack builds.