Battery DIRECT short feasibility

[Excaliber]

Inspired by the 300 amp circuit breaker thread, I offer a couple of personal life experiences, yes it happend to me!

#1. Four wheelin' in a Jeepster Pickup (Buick V8, a real beast). Battery NOT bolted down (young and foolish). Crashed into a tree coming down a hill (to fast, to stupid). Didn't crash "that hard", just a dent in the bumper, BUT, the dang battery came loose. The main + cable contacted the hot exhaust manifold, the heat melted the insulation! The cable now had a direct short to ground, and a GOOD one too! The cable insulation started to smoke and melt, both from the exhaust manifold heat AND the rapid discharge of the battery. The cable was glowing red hot, the insulation dripping off in chunks. I reached down to grab the battery and move the cable out of harms way, to late, the battery exploded! I narrowly escaped being hit by the shrapnel but took a face full of battery acid. I was instantly blinded by it all, my brother dragged me down the hill and threw me in the creek, which was perfect! I made a full recovery, as did the Jeep. There was no damage to any of the electrical systems, we simply replaced the battery and the cable and were back on the road! Piece of cake....

#2 My ERA Cobra!!! I was drilling with self tapping screws in the floor board, right above where the battery + cable was. Yup, screwed the + cable right to the floor of the Cobra! Terrific short, good and strong one, screwed it real good and tight, massive short. Now the fiberglass body doesn't have a real good ground connection, right? So, the path of the current was to every stinking ground wire on the car, burned a bunch of them up before I could disconnect the battery in the trunk. No other components were damaged, just the grounds, which actually still worked, everything worked, but the wires were all nekkid with the insulation burned off. Which is why the ERA has a new wiring loom... That was a few years ago, by the way. Be careful with those self tapping screws. The battery? It lived a long and properous life after that, worked good for another year or so.

#3 ERA Cobra, round two. The main battery cable runs from the trunk to the front, right next to the driveshaft. The drive shaft rubbed a break in the insulation, the main cable would, occasionally, "short" to the rotating drive shaft. It never gained a good enough ground to cause any trouble, in fact, I never noticed a problem at all. I just happen to see the "scorch" marks on the drive shaft one day and traced it down. Got lucky there.

Submitted to increase the general paranoia of battery shorts, carry on.

[DougD]

I was helping my brother change the oil on his Cutlass Supreme sometime back in the '80's. It was long enough ago that oil still came in cans. Anyway, he accidentally dropped the oil can spout down between the battery and the inner fender. That sucker contacted the positive terminal and literally welded itself to the inner fender. Had to hacksaw it off to get it out. The battery didn't explode - we were lucky.

[mkassab]

I guess the moral to the story is disconnect the ground wire from the battery before we work on our cars

Mark

[Rick Parker]

Ernie:

In cases 1 & 2 you demonstrated the absolute "FASTEST" method of "Discharging" a battery. Well done.

[Ronbo]

I think in the case of trunk mounted batteries you run a greater risk just because of the amount of extra cable involved. This one reason I never understood placing the disconnect switch on the dash as some folks have, it should be as close as possible to the battery.

[Excaliber]

Interesting question as to why the battery exploded on the Jeepster, from a rapid discharge. An over charge creates hydrogen gas (I think it's hydrogen?) which in turn ignites and causes the explosion, thats faily well understood. The need for venting such gases, etc.

Question: Does a rapid discharge also create explosive gases? What happens with a rapid discharge that would cause a battery to explode?

[twobjshelbys]

Originally Posted by Excaliber

Interesting question as to why the battery exploded on the Jeepster, from a rapid discharge. An over charge creates hydrogen gas (I think it's hydrogen?) which in turn ignites and causes the explosion, thats faily well understood. The need for venting such gases, etc.

Question: Does a rapid discharge also create explosive gases? What happens with a rapid discharge that would cause a battery to explode?

Heat. Lots of it.

[olddog]

I too have a battery in the trunk and admit the lack of ventilation is a bit unsettling to me.

Technically the battery does not explode. The hydrogen sulfide gas burns quite rapidly and pressurizes the battery case well beyond the breaking point. Explosion seems quite accurate when you see one.

[Excaliber]

"Burns rapidly", a slow moving bomb.

With todays sealed batteries ventilation does remain a concern, but not so much, it would have to be a worst case scenario. Severe over charging maybe. Or, screwing the battery cable to the floor, which of course is highly unlikely, uh, wait,,,,