Thermal Runaway on Purpose

Generic

Generic

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Oct 23, 2018
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So I've abused a lot of cells and have gotten close, but have never actually induced thermal runaway (thankfully). Iaccidentally shorted a high dischargecell that reached 235*F/112*C, but CID protected that cell. And on laptop cells that I've shorted on purpose, PTC has protectedthe cell from thermal runaway. Every thermal runaway video I've seen has either been a lithium polymer battery (no protection, Galaxy Note 7), mutilation (axing an 18650 in half), or externally igniting an 18650 with a propane torch or a heat gun (hi Daromer). I haven't tried overcharging a cell yet (think: hoverboards), and that's next on my list, but I'm just wondering if anyone here has accidentally or on purpose successfully initiated thermal runaway on an 18650 and how you did it?Unlike most of you, I'm dealing with generic cells and trying to do it in a safe way, so I'm doing a lot of independent safety testing, and besides shorting cells, I'm trying to figure out other ways to test my datasheetless cells for worst-case scenarios.
 
Generic said:
...but I'm just wondering if anyone here has accidentally or on purpose successfully initiated thermal runaway on an 18650 and how you did it?Unlike most of you, I'm dealing with generic cells and trying to do it in a safe way, so I'm doing a lot of independent safety testing, and besides shorting cells, I'm trying to figure out other ways to test my datasheetless cells for worst-case scenarios.
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Ive done it by using a motorcycle battery directly connected across the cell under testwith reversed polarity. This forces reverse charging at incredibly high current levels.The key to making it work was the use of very low resistance wiring/connections to ensure that enough current flowed to initiate thermal runaway before the CID or PTC protection kicked in. I used dual 4AWG wiring for both thepos and neg leads and 3/8 brass bolts for the contacts to the cell under test.

Im sure a good LiPo pack (or other low IR pack) could do it too. A 24V setup, or higher voltage, can be used to increase the current flow.

External heating is a foolproof way though as it allows bypassing all of the cells internalprotection devices.
 
Generic said:
Unlike most of you, I'm dealing with generic cells and trying to do it in a safe way, so I'm doing a lot of independent safety testing, and besides shorting cells, I'm trying to figure out other ways to test my datasheetless cells for worst-case scenarios.
Click to expand...

Did you decide on any particular methods yet?
 
I have not been able to abuse any 18650 till the point it goes boom except for with external abuse like heat. Over or undercharrg never worked since the cid took ovet before.

Lipo on other hand is easy to overcharge and have a nice fire
 
We fuse 18650's in packs in case one shorts out - to save the pack. Can individual LifePo4 prismatic cells 'short out' like 18650 cells? can this cause fire?
 
Life can Short too but they dont burn like liion. Risk is alot smaller.
 
The A123 26650 lifepo4 if you short it against the side of the cell where it punches a hole in it will catch on fire extremely well, I learned the hard way.The fire was comparable if not more violent then some of the 18650 cells I seen on videos. This short was accidental while taking the cells apart, the nickle strip shorted against the side shown in the picture. This is worst case scenario that can occur when disassembling packs of high discharge cells.


image_dxnxet.jpg
 
BatteryMooch said:
Generic said:
Unlike most of you, I'm dealing with generic cells and trying to do it in a safe way, so I'm doing a lot of independent safety testing, and besides shorting cells, I'm trying to figure out other ways to test my datasheetless cells for worst-case scenarios.
Click to expand...

Did you decide on any particular methods yet?
Click to expand...

Mooch, I decided that for basic testing, I'm going to use a 12V, 1A power supply directly connected to the battery to test for CID. If the cell has CID, it should pop. If it doesn't have CID, it should blow up.

Believe it or not, your example, while it seems to be an extreme example, is actually the reason why we fuse our cells despite their CID and PTC protections. Here's a NASAarticle that basically states that CID and PTC doesn't work in multi-cell and high-voltage packs like it does in single cell packs.So your motorcycle battery is not that different than having 299 cells dump current into a cell that has short circuited for whatever reason.
 
Generic said:
Mooch, I decided that for basic testing, I'm going to use a 12V, 1A power supply directly connected tothe battery to test for CID. If the cell has CID, it should pop. If it doesn't have CID, it should blow up.

Believe it or not, your example, while it seems to be an extreme example, is actually the reason why we fuse our cells despite their CID and PTC protections. Here's a NASAarticle that basically states that CID and PTC doesn't work in multi-cell and high-voltage packs like it does in single cell packs.So your motorcycle battery is not that different than having 299 cells dump current into a cell that has short circuited for whatever reason.
Click to expand...

Ive seen that NASA doc, thanks though!
So easy to overlook something like that when designing a pack. :)
 
This happened to my ebike battery over the summer during testing. Totally operator error, the bottom of the battery was hitting the water bottle holder screws I didn't take out of the bottom tube. I only noticed after my range went way down. These are 3.2ah 10a ncr18650db's (same tesla uses). Nothing catastrophic surprisingly. I was able to manually balance the packs then replace the damaged ones. Probably have like 150 cycles on it since then.


image_bixecs.jpg
 
I have accidentally (well rather, out of lack of basic safety calculation) caused a cell to go internal short, and go into thermal runaway. Luckily nothing too bad happened, I was able to submerge it in ice water until it drained itself out. Still a very scary experience, and one I wasn't really prepared for.


2:02 is just before the cell goes internal short (you can see the pack voltage drop from 26.5V to 22.9V). This was after 2 pack dead-shorts while trying to test the protection functionality of a BMS. There's more info on the slide at 19s in the video. The cell is an LG F1L (as far as I can tell with my visual and electrical test methods), though may not be a legitimate or "grade A" cell, since it was a rewrap from China.
 
You got lucky, that thing was really hissing! Looks like the CID popped too late. But the fact that you could hold it in your hand makes me think something else happened. When I accidentally shorted a high drain Samsung cell, that thing got up over 235*F/112*C, but it didn't hiss and CID protected it from getting worse. How hot did it feel in your hand?
 
Generic said:
You got lucky, that thing was really hissing! Looks like the CID popped too late. But the fact that you could hold it in your hand makes me think something else happened. When I accidentally shorted a high drain Samsung cell, that thing got up over 235*F/112*C, but it didn't hiss and CID protected it from getting worse. How hot did it feel in your hand?
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The body of the cell was not too hot, probably less than 60C which is about the tolerable threshold for holding. The short was definitely localized in the top cap of the cell. In retrospect I should have put the thermal cam on it, I forget if I had it at the time.
 
In that situation, you are only thinking about your own safety and about protecting the property around you from damage, should the cell explode or flare up. The last thing on your mind is "hey, is my thermal camera around?" Luckily I was filming the whole thing, so I was able to go back and see what exactly happened. As soon as I saw the puff of smoke, I got the pack I was working on outside and away from anything flamable, and that's when I noticed the cell was hot. Grabbed my cheap infrared thermometer and noted the temperature. Then I got my leaf blower and blew on that thing for at least 5 minutes straight.
 
Generic said:
You got lucky, that thing was really hissing! Looks like the CID popped too late. But the fact that you could hold it in your hand makes me think something else happened. When I accidentally shorted a high drain Samsung cell, that thing got up over 235*F/112*C, but it didn't hiss and CID protected it from getting worse. How hot did it feel in your hand?
Click to expand...

When I accidentally shorted a Samsung 13q the fuse burned and nothing bad happened.
I removed its cap and making a contact directly to the internal + worked, the cell was still usable.
 
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