LiPo and LiFePo4

[Freddyflatfoot]

Ok, I just saw a vid of a LiPo fire, from overcharging.
The vid was posted by a guy on another forum, in answer to LiFePo4 batteries being unstable.
I think he is mistaken, but so that i don't look the uninformed one, is he wrong?
Can LiFePo4 explode and burn?
Or is he confusing the two chemistries?

 

[TylerDurden]

Somebody here had a pack with A123 cells short...
http://www.endless-sphere.com/forums/viewtopic.php?f=3&t=3951&p=59821&hilit=

 

[Battboy]

We have tested LiFePO4 (LiFeBATT) Cells up to 180 degrees Celsius @ Sandia National Laboratories with no fire or explosion. All that happens
in a properly designed LiFePO4 is a puff of gas is emitted from one end because the cells are designed to "vent" and the LiFePO4
chemistry is intrinsically "safe". Not to worry - this was probably a Li-Polymer cell that you saw explode and they really go off like
a firecracker if they suffer from thermal runaway.

Don Harmon

 

[swade]

Somebody here had a pack with A123 cells short...
http://www.endless-sphere.com/forums/viewtopic.php?f=3&t=3951&p=59821&hilit=

Yeah that was me. I wouldn't say they exploded, more like they expanded when heated by the metal and wires and tape that was on fire due to shorting them out.

 

[Battboy]

Just curious - why do those cells look like they are wrapped with cardboard ?????

Don Harmon

 

[TylerDurden]

Just curious - why do those cells look like they are wrapped with cardboard ????? Don Harmon

That's why the links are in the posts, dork.

The diagnosis: my copper bus bars had shorted out on the side of one of the a123 cells that didn't have the original casing on it -- just some masking tape instead. (that's a longer story).

http://www.endless-sphere.com/forums/viewtopic.php?f=3&t=3951&p=59821&hilit=

 

[Battboy]

Sorry Dork - didn't see any explanation of the cardboard wrap in any links.

 

[kbarrett]

... dork.

... Dork, ...

Get a room, Funboys ...

 

[Toorbough ULL-Zeveigh]

cardboard is an insulator which prevents adjacent cells from making contact with each other & shorting out.

 

[Jeremy Harris]

Personally I think a cardboard wrap is a very good thing, much, much safer than the thin heatshrink on some cells.

Inter-cell shorts were a very big contributory factor in the battery fire I had with the original NiMH pack that I built. What happens is that when a cell gets hot, the heatshrink splits and almost disappears as it shrinks further from the heat. This allows adjacent cells to short, causing a chain reaction, with masses more heat and eventually exploding cells.

At least cardboard is relatively immune from this sort of effect, which may well be why so many industrial-type cells use it. The added advantage of cardboard sleeves is that they usually have the positive end folded over, so providing a good end-cap insulator, preventing shorts from battery connection tabs.

Jeremy