2003/2/9 Lithium Polymer got fire Return to top.

What will happen if you charge 2 cell at 3 cell setting? You get trouble.

I have been using the beta version of Lithium Polymer cell (E-Tech) in 2 cell pack and flew great. Last night I made a mistake to charge 2 cell pack as 3 cell, and after 30-40 minutes or so, it got swelled, smoked and got fire in bad way. Here is what happened and analysis.

What happened.
- I use Lipo packs in 2 and 3 cell combinations. Charging with dip switch setting of Apache charger to appropriate way. When I came from field after all day flight, I was tired and made mistake in switch setting. I was charging in my room and away at other room.

- Noticed a sweet paint or gas like smell first. Checked the battery. It swelled and blowing off white gas like a smoke spot. I quickly disconnected but gas did not stop. In a few seconds each cell got fire one by one blowing lots of flare and sparks like fireworks. I picked up and threw out to Veranda.
- Luckily I could extinguish fire easily. Resulted burned thumb and many burned spots on carpet.

Analysis
- Lithium Polymer cell behaves badly when overcharged. It gets fire by itself with flare. The flare itself is burning and light, can expand fire. I think this is common in all lithium polymer cell as it has layered thin metal sheet in it.

Did I abuse them? maybe. The exact cell packs were over charged once in the same situation at bench for 10 minutes or so. The cell did not swell but may have been damaged internally. I have been flying them at max of 5-6A without noticing performance loss.

- Charger sometimes does not detect cell count. Although it needs to be manually set with dip switch, I observe it has voltage checking before charging to prevent wrong setting. Still it does not detect correctly half charged cell because Li+ cell has very wide voltage range. (This issue is addressed with production version of Apache charger. It has very strict voltage checking and will not make mistake. Good! All Li+ charger should follow this.)

This is a nature of Li+ charger and we need to be careful. .

I have been using metal Lithium Ion cells for over a year by charging one cell charger in parallel without any problem. This trouble happened because I started using mix number of cells. Need caution.

- Do not charge unattended, nearby flammable materials.
- Set charger manually, check setting again before charging to make sure.
- It might be better to prepare separate charger if you mix 2 and 3 cell packs.
- Do not use automatic setting charger, do not use multi mode charger that charge Ni-Cd, Ni-MH.

Sasaki

Photo to be posted later.

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