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[hoverboy]

Hi,

I have just had a Ni-cad 8v battery catch fire on me. All I done was to connect it up in my boat as usual, something I have done many time before.  After i removed it I put another batter in and all was OK.

Has anyone else experienced this or can anyone explain what went wrong? I have attached a picture.

Pete

[Martin (Admin)]

I've had a couple of burn up.... usually insulation was damaged or a cell just committed "Harri Karri !"

Have you tried another battery to (carefully) check the motor and Speed controller are OK?

[andrewh]

Hoverboy

Terribly tentative conclusion is that the burning was the red insulator fibre - hence the blackening.
 I dunno if you pulled the end cell off, or if it contributed by falling off?

Looking at the cell connections they are by 4 or 5 spot welds - this is a non-recommended way of passing huge currents since the area available for conduction is quite small.  (the big-current boys used soldered braid or Litze wire connections if they can't solder cell to cell)

 So tentative cause - one of the welds failed (possibly the end cell was able to move and strained the welds) the current overheated the remaining weld or welds enough the ignite the fibre insulator.  Both sides are equally hot and blackened so it is not outgassing (hydrogen) burning (the hydrogen vent is in the positive cap)

Not necessarily right, but hope the thinking may help
andrew

[hoverboy]

Thanks Martin. Hope that was all it was.

Andrewh.

Your comments are interesting. The battery cells were firm as they were in the outer case as supplied by the manufacturer. I have just looked at another battery from the same company and found the negative wire was badly carroded  all the way from the battery to the connector. The positive was OK These batteries were about three years old.

Pete

[SteamboatPhil]

Always worth checking all connectors (negative getting hot=very bad) as over time they do corrode and become loose, can cause your fault, plus lack of performance.3 years use, not bad though.

[malcolmfrary]

I have just had a Ni-cad 8v battery catch fire on me. All I done was to connect it up in my boat as usual, something I have done many time before.  After i removed it I put another batter in and all was OK.

If the welds failed, then both sodes failed simultaneously.
Did it fire up on insertion, or was power being drawn?
It could have been an insulation fail between the two end longitudial cells.  Tis would give a very large current at that end of the battery.

[hoverboy]

All I done was to plug the battery in. Everything happened so quick. At the time I was bench testing the system in the boat to check all was well. My main concern was to get it out of the shed.

Pete

[DickyD]

Wouln't have anything to do with the fact your lawnmower hovercraft has been starting up on it's own Pete.   

[BobF]

As you say only the neg wire was faulty, I think this could be Black wire syndrome. This is caused by damp. Some new cells suffer from this, if they are not stored in dry conditions. If the cells were damp then as already mentioned, it is most likely the insulator failed between cells. Black wire would not cause the fire, but leads to no power from the battery in worst cases.