Fire Hazard: Nil If Battery Not In Use?

Does the fire hazard on batteries go away when the battery is neither being charged nor discharged?

i.e. Should I be parking my ebike in the garden shed instead of the garage?

A lot depends upon the chemistry - I believe that LIPO batteries can be unstable and a possible fire hazard if the cell voltage falls below 3 volts. LIFEPO4 and SLA are fire resistant but probably not good for any battery to sit fully discharged for any length of time.

if the battery pack is " open circuit " ie : no bms, no charger, nothing connected what so ever... chances of it going ballistic on you are extremely slim, but not impossible.

critters chewing on wires, water leak in just the right spot, external elements can also come into play.... again... unlikely but possible.


it's like the polar oposite of winning the lottery......

if you have a lifepo4 pack there is no fire hazard from the pack but you have to worry about shorts which is how most of these fires start anyway. lipo is vulnerable to thermal runaway if overcharged above 4.2356V or so and the thermal runaway can induce thermal runaway in adjacent pouches so you could have a fire break out then. lipo does not ignite from being discharged and 3V is not fully discharged for lipo. 2.7V is fully discharged for lipo.

that's not an absolute...

i've taken HK 20C lipo cells to 5V+ without drama... and then discharged them to 0v.. and recharged that same cell again, no fire.

http://www.youtube.com/ypedal

got video's documenting the whole thing.

http://www.youtube.com/watch?v=hg_8sVXxIsw&list=UUJCgYcCXBAuxEgVT1bpMnyQ&index=27

part 1 of a multi part abuse test series.

part2
http://www.youtube.com/watch?v=o5QHEO6wFm0

i agree, it is not an absolute. i have overcharged lifepo4 too without killing them also. but i used the term 'vulnerable' to reflect the literature documenting the conditions which lead to thermal runaway. i do not have direct knowledge of what it takes to ignite them, just what the literature states.

The main concern with Lipoly sitting unattached to anything drawing power is that if the cell decides to puff (impurities?) there's a very real risk that the tabs on cells can short and send things into a very dire situation.

Is it likely to happen? Not in my opinion but watching for puffers and leakers (cells who self-discharge) is probably a good habit to develop. Along with storing long term in relatively fire resistant areas.

I believe a cell is also more likely to puff or otherwise become damaged in storage if it is at a higher temperature. I don't think there's any real likelihood that a cell that you've tested and used will randomly vent while just sitting, but storing at a lower temperature may help them last longer.

dnmun said:

lipo does not ignite from being discharged and 3V is not fully discharged for lipo. 2.7V is fully discharged for lipo.

Click to expand...

I'm really afraid some might take this as fact, Most manufacturers don't recommend discharging lipo below 80% dod. Now that's about 3.7V. All this 3V and 2.7V talk is max c rate load voltage, not resting voltage, at which most of us check our packs. At 3.5V you are very close to 100% dod. IOW's very very close to being fully discharged. At 3.0V resting you have over discharged you battery. Expect a way shortened life cycle. At 2.7V resting, not only have you shortened your life cycle, but you're in the range where more high load could end in disaster if you try and pull another high load from it. You don't have to believe me. Just hook your charger to a battery at 3.5V and check it's soc. It should show less than 5%. Probably more like 1-2%.

it is fact.

But they might get pretty hot and melty around the shrink wrap as they go below 2.7v though. Mine didn't catch fire going to 0v, but they did vent stinky stuff that might have flamed.

but has nothing to do with the original question. lifepo4 would more likely just puff and stink if something happend in storage. When I killed my first pingbattery, I parked it 90% discharged, then forgot to turn off the controller and left it for 3 weeks. The 3w drain took the whole 36v pack to 0v. In my garage, attached to my house, but all it did was swell up to unbelievable size. Nothing was melted, not even easily melted duct tape.

why would anyone discharge a lipo below 2.7V if that is fully discharged? i did not make up that number, it is documented. it is just the tourists on the sphere who decided that 3.5V is fully discharged.

i know most manufacturers recommend not going below 3V, and the RC guys swear by 3V, but the number in the literature is 2.7V. this is the number that used to be considered accurate by experts here before this place changed.

dnmun said:

why would anyone discharge a lipo below 2.7V if that is fully discharged?

Click to expand...

DogMan's observation rang true to me: accidental discharge via parasitic load by the controller.

3.5v per cell is a good place to stop discharge while under load. It is also where the HK packs tend to start getting out of balance, increasing the risk of damaging a cell without a BMS. There is still energy left in the pack, but I prefer to stop with 10% left unless all cells are monitored. On a large format pack that is 1p, I would probably run it down to 3v if there was a BMS watching over me.

dnmun said:

it is fact.

Click to expand...

Prove it. And I'm not talking about the wikipedia article. I'm talking about from manufacturer specs. I don't remember which manufacturers site I got the info from, but they did not even come close to agreeing with your "facts". I do remember they recommended an under load cutoff voltage of no less than 3V and recommended 3.5V. From the hundreds of discharges of lipo packs I've seen, including my own, I think you have your "facts" confused. You are doing no one a service with your "facts", and anyone using your values as fact will soon find themselves with damaged lipo battery packs.
http://www.rchelicopterfun.com/rc-lipo-batteries.html
OVER DISCHARGING - THE NUMBER ONE KILLER OF LIPO'S!!!

The other thing that will heat a pack up fast is if you push it right down to or lower than 3.0 volts per cell under load. Even if you have a 40C pack and can only draw half that amount, if you push it hard right down to 3 volts per cell - it will become very warm/hot and will shorten its life substantially.

There are literally hundreds of post like this on the web.
http://www.fesselflug.eu/html/battery_questions_answered.html
5. What is the lowest safe discharge voltage of a Lipo cell?

Standard Lipo batteries should only be discharged to 3.0 vDC per cell, measured under load. Example - discharge a 5S 1800 battery to 15 vDC; 3.0 x 5 or 15 vDC. Many folks set the low voltage cutoff on their ESC to 3.2 vDC per cell - this is conservative but I think prudent. In our example this would discharge to 16 vDC under load. The place to control this is in your ESC setting.

For damn sure I never meant to run a nice battery dead. When I parked that bike and forgot to unplug, I was running a 104 F fever, the day I got west nile.

Before I learned to dilligently tape the plugs of lipo packs I was connecting paralell, I ran a few lipo packs to 0v. One plug pulled loose, and now I was riding along with a 5 ah pack, thinking I was fine with 10 ah. Both times no fire, but the overdicharged pack definitely got very hot, and melted the shrink off the bundle.

I store my lipo's in a fire resistant metal box, outside or on my fireplace hearth. Just in case. I've parked a lifepo4 pack in my garage with no worries, since 2008. It happens to be mounted on the bike inside a metal box, which hopefully will help if I have a big problem. But it's parked near plenty of flamable stuff, like the painted sheetrock.

IIRC, JohninCR had a cell go thermal just sitting on the shelf.