Puffed LiPo - when to start getting worried...?

[james_s]

I don’t really know... but honestly, on my bench, I prefer a Lipo or something smaller...
The battery type doesn’t matter much I think, the point being more what current it can deliver, can a (typical) lead-acid battery deliver in excess of 800A ?

Yes, a starting battery certainly can, especially the sort that would be used in something like a diesel pickup truck, even a conventional medium sized car battery can likely manage though. The downside is that lead acid is bulky and very heavy and they can be dangerous, flooded cells will leak acid if tipped and they give off corrosive vapors and produce hydrogen when charging. They are extremely robust and can take a lot of abuse though.

[Berni]

Yeah if its puffed its on its way out.

But it doesn't mean that it will spontaneously catch fire when left alone on a shelf. But if you continue stressing it so much it might puff up even more and at some point cause enough of a current concentration inside to create a hotspot and start the runaway self destruction. Tho physical damage tends to be a much easier way to start this self destruction process.

In any case even a brand new perfectly fine looking LiPo pack should be treated with care, especially these RC packs that are protected by nothing else than foil. All it takes is dropping a heavy or sharp object on it and it has a pretty good chance of suddenly catching on fire.

[Siwastaja]

Could you provide some data to back this up? It's not just me, there are thousands of people flying models with LiPo packs, a handful in the community have had fires, about 90% of those occurred while charging and almost all of those that I've seen were charging without the balance leads connected.

Note that "a handful" out of "thousands" is roughly 0.1% meaning you are agreeing with my numbers! You just need to apply logic instead of emotion.

A proper cell does not typically go up in flames while charging, even if electrically abused. They have passive safety layers; which are not perfect, of course, but make a big difference between a cheap Chinese product made in a no-name factory vs. a Panasonic or Samsung cell with decades of R&D and responsibility by the manufacturer.

It's hard to protect against physical damage, like a copter crash; but during charging, having catastrophic failure is almost inexcusable, even if the charger does something wrong. Yet as you say, these crap cells fail while charging. It's a clear sign of lack of passive cell-level safety including shutdown separators, CIDs and PTCs (and likely modern and proprietary things I'm not even aware of).

The fact the same people who sell these crap cells, also sell fire-proof sacks and stainless steel bunkers for charging, tells the whole story. They make a business out of the well-known unsafety of their own products.

No one has actual data about this, obviously. The many orders of magnitude difference in safety between proper cells inside hunderds of millions consumer device, vs. "almost everybody has seen or heard about someone (2nd or 3rd hand) having a fire" in the Hobbyking hobbyist scene, should be evident.

Similarly, it's very typical that when a phone goes up in flames generating headlines, it's almost always a cheap replacement cell that was used; even if the percentage of such replacement cells inside the devices is minuscule. Hence many orders of difference in safety. But again, no one has hard data on this.

Do note, I have absolutely nothing against these Hobbyking products and do use them myself, they have their place. I just don't like mental dishonesty.