21700 in my Sofirn SP35 suddenly died

Bright+

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Reads 0.0v and I can't get it to charge. It was in my jacket pocket. I think it may have gotten switched on in the pocket and stayed lit on high.
The light itself powers up "tethered" with charger hooked up.

When I apply about 5v directly to the battery, it doesn't take-in any current, which suggests to me the protection circuit is tripped. Do some batteries have a thermal switch? I am wondering if it got hot when it lit up in the pocket to the point of popping an internal thermal fuse.
 

vicv

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The internal fuse is called a PTC. Doubt it popped though. That's more for like a dead short. I'm going to say the protection circuit went bad. But putting 5v directly to the battery won't work either. The protection circuit, if good, would stop it
 

Bright+

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The internal fuse is called a PTC. Doubt it popped though. That's more for like a dead short. I'm going to say the protection circuit went bad. But putting 5v directly to the battery won't work either. The protection circuit, if good, would stop it
Oh, it was the CID. Shortly after I made this post I followed the CID reset YouTube and the cell was revived. The battery had 3.8v left. The video is at https://www.candlepowerforums.com/threads/cid-protection-reset-18650.434728/#post-5103100
 

aznsx

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EDIT: You should I would dispose of that cell and attempt to use it no further.

Keep in mind that PTC stands for 'positive temperature coefficient', which is really an electrical characteristic (used like an adjective), and in this case really should be followed by a noun. The most common type are called 'PTC resistors', which limit current over a certain designed threshold level (by instantly increasing their internal resistance dramatically when current over their designed threshold is reached), are often referred to as 'self-resetting fuses', and therefore do generally auto-reset with no action required after the overcurrent condition clears. I don't have such off-hand knowledge of 'CIDs', and therefore cannot comment regarding those.

Under-voltage (vs over-current) protection devices / circuits generally do not self-reset, but may be reset by application of external voltage, which is what chargers capable of it do to reset those cells which have 'tripped'.
 
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aznsx

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Once resetting a defective cell, now without a functional CID, next time overheated there's a good possibility the cell will runaway?

I wouldn't want to take that chance.
Sure, just stick a penny in the fusebox next time one of those blows too while you're at it. NTF (no trouble found;-).
(Some may be old enough to remember those old thread-in [Edison base?] fuses. I'm sure you've never seen one, KG.):)
 

Bright+

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Especially for about $5
Once resetting a defective cell, now without a functional CID, next time overheated there's a good possibility the cell will runaway?

I wouldn't want to take that chance.

I don't plan on putting it back to use. I reset it, because I wanted to know what failed.
I'm thinking the flashlight got hot enough from accidentally getting left on inside the pocket and "cooked" the battery hot enough to pressurize it.

I feel that Sofirn should have designed thermal foldback to prevent this.
 

aznsx

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I'm thinking the flashlight got hot enough from accidentally getting left on inside the pocket and "cooked" the battery hot enough to pressurize it.

You could very well be right about all that, but it seems you may be making an assumption that the root cause was overheating due to the light's having being 'on' (unintentionally), which again, might be the case, but seems hardly the only possibility. Unless I'm missing something however, it might also be due to an internal failure, within the cell itself, which caused the overheating. If that's the case, your flashlight may not have any blame in this at all, and it may just be the safety circuitry doing exactly what it's intended to do (among other things), which is prevent the cell from doing the 'china syndrome' thing due to an internal short / severe overload condition.
 

Bright+

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You could very well be right about all that, but it seems you may be making an assumption that the root cause was overheating due to the light's having being 'on' (unintentionally), which again, might be the case, but seems hardly the only possibility. Unless I'm missing something however, it might also be due to an internal failure, within the cell itself, which caused the overheating. If that's the case, your flashlight may not have any blame in this at all, and it may just be the safety circuitry doing exactly what it's intended to do (among other things), which is prevent the cell from doing the 'china syndrome' thing due to an internal short / severe overload condition.
Highly doubt internal short. After I pushed the button back in per video, the cell had 3.8v and the light worked for considerable time. I think internal short would've drained the cell.

Severe overload would've only happened due to engineering flaw. It was a Sofirn light with Sofirn battery, so it would indicate an engineering failure of pairing these two.

This being said, does anyone want to try out their fully charged Sofirn SP35 on "high" wrapped in fiber glass insulation (so it doesn't burn) and see if they can replicate this fault?
 
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aznsx

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Highly doubt internal short. After I pushed the button back in per video, the cell had 3.8v and the light worked for considerable time. I think internal short would've drained the cell.

Severe overload would've only happened due to engineering flaw. It was a Sofirn light with Sofirn battery, so it would indicate an engineering failure of pairing these two.

This being said, does anyone want to try out their fully charged Sofirn SP35 on "high" wrapped in fiber glass insulation (so it doesn't burn) and see if they can replicate this fault?
Not me. I wouldn't even do what you've already done. Life's too short, and cells too cheap. Have fun though!
 

knucklegary

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Being it's a Sofrin cell. I'd contact them, they're fast to reply, have a replacement 21700 sent. Then try to replicate what happened?

...but not in coat pocket 🙏
 

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