the expanding lipo! questions for the lipo gods

[Semi Pro]

so i have a lipo pack that is puffing alittle every time i use it, after its recharged and sits over nite is shrinks back down to its normal size.


is it really safe to run it?

i have never had a pack do this, is it normal?

what could have caused it to start doing this?

the pack looks like new, its never been in any crashes, and it has only been run 20-25 times,

[brushlessboy16]

I had this happen to a zippy pack, as long as the cells hold voltage and stay balanced you are fine.

[BrianG]

Expanding lipos means they have been/are being pushed too far. Sounds like they are heating up too much, which means you are pulling too much current. Or, your LVC could be set too low.

Either way, I personally wouldn't use them.

[Semi Pro]

afew more questions brianG

how hot is to hot, it has never gotten above 120*

the pack is 35c i cant be drawing that much with a mmm and align 600xl 1600kv could i?

my cut off is set at auto lipo, should i raise it alittle, i normaly never hit cut off and stop with about 20% remaining (how high on a 5cell to reall make a diffrence?)

[BrianG]

120* is probably on the upper end of what I'd run, but it's not terrible. And the amount of current draw is going to depend a LOT on gearing. Even a low kv motor can pull substantial current when geared high.

What batteries are these? I'm wondering if they are simply overrated and more like 20C or less.

Unless you use the new firmware (I assume this is using the MMM), auto lipo is set to 3v/cell IIRC. Either set it to manual 3.2v/cell (16v for a 5s pack), or change the auto-lipo cutoff value to 3.2v in the new firmware. Most of a battery's heat is generated near the end of the run where its internal resistance begins to climb. If you increase the LVC point, the battery will cut off before the cell resistance gets too high, and will stay cooler.

To be clear, I don't know if making these changes will help the questionable pack. It may have weakened.

[lincpimp]

Sounds like maxamps... I am betting the label fell off the pack, cause we all know that the label determines the C rating on maxamps packs, not the actual cells.

If it is puffed it is done, either toss it, sell it () or use it for a roto start or a low draw app like a crawler.

[simplechamp]

Don't you guys worry about the cells exploding and starting a fire?!??! I know lipos are pricey, but personally I wouldn't risk my home and personal safety to try to salvage a puffed lipo.

[lincpimp]

Nah, I fool with puffed lipos all of the time, and no explosions yet. Got a little smoke when I hooked 1 cell to a car battery, HEHEHE

[simplechamp]

I don't have enough experience to know how likely puffed lipos are to explode, or the overall safety of lipos in general. All I know is that the warning labels and youtube videos of exploding lipos have scared me enough to not take any chances.

[BrianG]

So far the worst I got was small flames, a lotta smoke and a pile of ash. I've even TRIED to blow some up. Mostly, I just get an instant puff and a whole lotta smoke (enough to thickly cover a city block). Luckily I did this at night and near the 4th of July where it would be less noticeable. Anyway, this was done by driving a nail into the pack and moving it around so it shorts the internal conductors. Of course, if you do this kind of thing where there is "fuel" (flammable stuff like plastic and such in a vehicle), the whole thing will go up if you do something bad enough.

[simplechamp]

I would say if you insist on trying to salvage the puffed battery make sure to use a lipo safe-bag, safe-sak, etc. or a bucket of sand when charging (I think a lipo bag should be used whenever charging a lipo; new, old, or puffed).

I didn't join the forums to preach lipo safety, but I think people really underestimate how hazardous these batteries can be without the proper precautions. Even with safety measures there are still risks.

[Unsullied_Spy]

I would toss the pack. I had a Maxamps pack (2s 6000 mAH) do the same thing to me and it just got worse. A few runs after I noticed it was puffing it was puffed enough to put strain on the battery hold-down in my Rustler. I figured after a while it wouldn't be able to handle it anymore and would do something a little more spectacular so I stopped using it.

With that dead pack I took the shrinkwrap off and threw it at the ground as hard as I could. All the cells flew apart in different directions and bent pretty badly but no massive explosion or anything like what you see on YouTube. My 2nd Maxamps pack that went bad was a 3s 6000, and it got a much more deserving end. All that happened to that pack was a whole lot of smoke.







I love sharing those pics, good carnage If that wasn't enough to get flame, I doubt they are really all that volatile. My 3rd and 4th Maxamps packs died a less spectacular death, they just got worse and worse at staying balanced and wouldn't take a full charge so I sent them back. 5th and 6th packs are still going, they will probably get the same treatment when they kick the bucket.

Bottom line, toss the pack. Good lipos are getting cheaper and cheaper all the time, it's not worth the risk IMO.

[Semi Pro]

well so far the pack is still hanging in there, i letting some buddys use

brianG

you said gearing had alot to do with it, my buggy was geared for 35mph, i guess im alittle suprised still that it puffed