storing lipos

There is a very simple explanation. All the commercial applicatons employ safety devices built into the battery pack. Note that none of the "majors", Sanyo, Panasonic, SAFT sell bare lithium cells directly to the hobby market. They do not want the liability. Lipo cells do not spontaniously self-destruct. There must be an external stimulus. Deep dischare, short circuit, overcharged etc. to initate an incident.

Lithium packs made for commercial accounts have safety circuits built into the battery pack. Notice you don't see the majors like Sanyo, Panasonic or SAFT selling raw cells directly to the hobby market. Lithium packs do not self destruct without some external influence. Shorts, overcharge, too deep a discharge, physical damage, are some causes of lithium battery incidents.

-- Red S. Red's R/C Battery Clinic

So what about what I'm hearing about lipos catching fire for no other reason than being in a hot car? There are very few accounts of this specific scenario, but they exist.

I think the key issues that have been identified are that hot lipos produce gas, and deform. They are supposed to then pop and vent the gas, but sometimes the pressure doesn't result in proper venting, and the cells short internally under pressure, go red hot and woof.

The key is to keep idle packs at less than 75C. More than that and they are destroyed anyway, and may, if they short, catch fire was well.

Packs used in cell phones are designed for lower discharge rates and don't either have the same liquids in them that gas, or have the electrodes so close together that shorting out internally is such an issue.

We discussed this at length on the e-zone.

The tentative hypothesis that fits the facts is that the cells distorted under the heat, and shorted internally.

Was the switch left on perhaps? Was there any study done to determine the actual cause? There are far too many of these I knew a guy that knew a guy that . . . . . . . . in this hobby . . . . . Can you give us the benefit any details of one specific account? Otherwise its hearsay. . . not admissable evidence. The CPSC would love to hear about any spontanious "incidents. Sounds like more of Dave Brown's "models being flown at $25,000 feet". :-)

True, you have to rely on heresay in these matters, and it's nothing that will hold up in court. But I never heard these stories with Nicd or Nimh. I also never went to bed wondering if my shop was going to be there in the morning, firesafe or no. I have 7 lipos now, and I love their performance. I'm taking all the precautions I'm supposed to and hope that this is getting overblown in some way, and that the spontaneous combustion stories have more to them than meets the eye.

| True, you have to rely on heresay in these matters, and it's nothing | that will hold up in court. But I never heard these stories with | Nicd or Nimh. I

Then you haven't listened very carefully. It does happen, it's just rare.

I'm guessing that *more* NiCd and NiMH cells have caused fires than LiPo batteries over the years. Probably the number one cause is something that shorts out the pack, either internally or externally, causing something to get red hot and start a fire. Damage to the pack and poor wiring would be the likely culprits.

Of course, my statement is rather misleading -- NiCd and NiMH batteries have been around a lot longer than LiPoly, and I only mentioned LiPoly and not LiPoly/LiIon. Also, when something goes wrong with a NiCd/NiMH pack, it's normally not the pack itself that burns but it starts something else on fire. But even so ...

Its all discussed on te E-zone.