NASA blows up a lot of 18650 batteries

Batteries and Chargers Rechargeable Batteries
1

Stumbled on this. Interesting reading. Essentially NASA torture tests 18650 li-ion batteries (overcharging, undercharging, over-discharging ’em to 2.0 volts) and blows up a lot of 18650 batteries in the process!

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CFYQFjAB&url=http%3A%2F%2Fntrs.nasa.gov%2Farchive%2Fnasa%2Fcasi.ntrs.nasa.gov%2F20100037250_2010040765.pdf&ei=7a4aUPWMNeHNiwLygoFY&usg=AFQjCNELfn3dK70CnEe8JZ-unGxMXwfB0A

I don’t have time to read and absorb it right now, but in one series of tests, they over-discharged 18650s repeatedly to 2.0 volts. Unless I’m reading this wrong (which could well be the case), SINGLE overdischarged cells survived just fine (even after an overcharge to 4.4 volts), but over-discharged cells IN SERIES were a different animal:

“If the capacity removed from the unbalanced cell was 100 mAh or greater, the series configuration test modules with the unbalanced cells displayed different behavior. If the capacity removed from the unbalanced cell was 100 mAh or greater (50 mV or greater imbalance), the cells did show internal shorting at some point and this caused instability in the whole string or abnormal behavior in some.”

Nice having NASA testing 18650s for BLF! Your tax dollars at work (for those in the U.S. anyway)!

2

That’s why we need PCBs.

3

Well, that was interesting for sure. Some definitely destroyed batteries. Also, some reached 600C+, that’s insane.

4

I red some parts, it is very interesting.
Thanks for sharing

5

If I read this right, then they said what we’ve always known. You gotta watch out for harvesting laptop batts. If they are connected in series (which I think they are?), then if they are overdischarged, then you got BIG problems if you use em in two-cell lights. But you shouldn’t even use them in one-cell lights.

“……the cells did show internal shorting at some point and this caused instability in the whole string or abnormal behavior in some.”

Weird that you can overdischarge them singly and you’re fine. If I’m reading this right. So if you overdischarge em to 2.0 volts less than 75 times SINGLY in a light, you should be okay. I wonder what the “in series” over discharge does to mess em up?

6

I believe when you overdischarge a string of batteries in series, the battery that goes depleted first then has the current of the remaining cells passing through, and this act like a reverse polarity recharging, e.g very bad for the battery health. A single overdiscahrged cell can only drop to zero volt, but then it’s subject to no other reverse current so the internal damage is somewhat limited…