Why a fire extinguisher is a good idea...

[Rhod]

Earlier this week I fitted a new Exrider 105AH battery into the Mazda Kitchen Unit. The battery terminals were on the opposite sides to the original, so I extended the +ve lead to let it reach. Today I used the Bongo for the first time since fitting & drove the 4 miles into work - everything seemed ok. Driving back this evening, prior to heading off to Galloway for the weekend, I was almost home when I noticed the Leisure Battery cut-out switch LED (Still Desperate modification) on the dash flickering. At the same time I got a smell of burning plastic & saw smoke in the back of the van. I hit the hazards, leapt out of the front & back in the side door, grabbing the extinguisher en route. Opening the battery compartment door on the cube, there were flames licking up from the battery leads The extinguisher did it's job. I disconnected the -ve lead & drove home - to spend the next 2 hours cleaning extinguisher powder out of the kitchen unit. They don't half make a mess, but I hate to think what would have happened if I hadn't had one

The circuit has obviously shorted out somewhere, but where & how
On the Mazda Cube, the +ve & -ve battery leads are seperate only for a few inches before they are wrapped together into the loom. The -ve lead has broken about 2" beyond this point, inside the loom. The ends look almost as if they had been cut, and I doubt that the heat of the fire would have been enough to melt the copper, or that the break would look so clean. So the question is, could a break in the -ve cable which was making & breaking contact cause heat which would break down the insulation on both leads, resulting in a short across them?

[francophile1947]

I suppose that it's possible that the flowing current could result in arcing between the gaps - that can certainly generate a load of heat that could melt the plastic insulation.

[Rhod]

Thanks John - useful input.
I should add that lights, fridge etc were all switched off, although the monitoring system does take a small current from the battery.

When I extended the +ve lead I used a blue butt-join crimp connection because it was the only one I had handy. I intended to replace this with something beefier to be on the safe side. This doesn't appear to have been the source of the fire however & I'm fairly confident that it would handle the current loading in any case. Extending the lead did mean that I stretched the cables a little during the process, so this could have been enough to pull the broken ends of the -ve lead apart I suppose, leading to arcing.

[mikexgough]

every vehicle should have one and when they are £6.68 at Lidl...... no excuses....

I suppose as safety devices like Triangles,Hi Viz vests (CE approved),Bulb kits, Extinguishers and First Aid Kits are treated as an optional accessory in the UK rather than a legal requirement, UK driver ignore having these valuable devices in their vehicles....

As a driver who travels Europe, I have all the above and a spare pair of specs too.....

Glad you managed to kill the fire.....

[northerntaff]

Can't help you on the techie side of things, but damn good job you had the extinguisher...well done on averting a complete disaster

[cheffy34]

Good show with the extinguisher a brake glass hammer is another good one to have


Dar

[munroman]

Hi Rhod, the extra resistance caused by the frayed/broken wires would lead to heating at the weak spot, so it could easily have melted through the insulation at this point.

As I have a factory kitchen guess what I will be checking in the morning!

Glad that you saved the situation, well done for the quick reactions!

[mikeonb4c]

Phew. I broke out in a hot sweat reading this. Well done Rhod and his extinguisher for saving the day

Nothing beats soldering and heatshrink tubing when the going gets serious I reckon. Maybe solder in a new run of wiring with some extra spare length, starting from a safe, unstressed point some way back up the loom. And is a fuse right by the +ve terminal a good idea so any naughty stuff like that is prevented from getting out of hand? Maybe also one of those isolator terminals if battery not needed for a lot of the time?

[Rhod]

Time for an update..
Just spent the day stripping out the Cube in order to fit my spare loom. In addition to the possible broken -ve lead, there was also bare wire showing at the point where the 2 battery leads join into the main loom. The loom is stressed at this point as it tries to turn in several directions & there are also a few sharp metal edges around. I'm pretty sure that the loom has been rubbing at this point & has shorted out, although the fire seems to have started further up the spur at the broken lead.

My new loom is routed very carefully, has half a roll of insulation tape reinforcing suspect points & every metal edge in the Cube sub-frame has piping protectors

The original loom had butterfly nuts on the connectors, which meant a panic disconnection was easy. The new one has nuts, so I'll be fitting a quick release set as soon as I can get hold of them.

An inline fuse beside the battery, as Mike suggests is a good idea & is also on my shopping list.

I still need to extend the new loom so that the +ve lead will reach the terminal. I don;t really trust my soldering on such a critical connection. Any suggestions on an alternative connector? Was thinking of a yellow butt-join crimp connector - I think they're rated at 30A plus?

Off to the chandlers tomorrow to replace my fire extinguisher!