Jump starting a car

Forums › Transport (cars, bikes and boats) › Jump starting a car

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946 posts

Ultimate Geek

#657960 18-Jul-2012 19:51

I was a qualified mechanic for 10 years a long time ago and I jump started quite a few cars. Some directly to the battery, most to engine.

Sealed batteries are NOT completely sealed, I have opened them up and YES they do release gas.

The risk of explosion is very very very small, it is not the main reason why I prefer to attach to a lifting bracket and I have seen a battery explode, well I heard it then saw it land. Another mechanic was welding nearby and the battery that was supposedly dead was sitting on the floor a few metres away.

I am done trying to explain what I know against what you assume. You take the risk, I really don't care.

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#657965 18-Jul-2012 20:01

riahon: I was a qualified mechanic for 10 years a long time ago and I jump started quite a few cars. Some directly to the battery, most to engine.

Sealed batteries are NOT completely sealed, I have opened them up and YES they do release gas.

The risk of explosion is very very very small, it is not the main reason why I prefer to attach to a lifting bracket and I have seen a battery explode, well I heard it then saw it land. Another mechanic was welding nearby and the battery that was supposedly dead was sitting on the floor a few metres away.

I am done trying to explain what I know against what you assume. You take the risk, I really don't care.

And myself I'm a qualifed Electrical Engineer, having worked in this area for over 25 years. As for the exploding battery you mention, most likely a hot blob of molten metal from the welding landed on the battery, melting thru the plastic and the electrolite igniting.

riahon

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Ultimate Geek

#657970 18-Jul-2012 20:06

So did the electrolyte explode or the gas explode?

jeffnz

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#657975 18-Jul-2012 20:20

if a battery has been charging it will produce gas (hydrogen) which is explosive, electrolyte or sulphuric acid isn't flammable.

Generally the amount of gas is minimal but if the battery has been discharged a fair bit it will be working hard to recharge therefore producing more gas. It can sometimes only take a short on the terminal to ignite.

SMF or sealed maintenance free batteries have a baffle system which , which gas is made, is routed round the baffles whereby it generally cools down and returns to liquid state and goes back inside the battery. Excessive gassing will be released from the 2 safety exhausts usually at either end.

Low maintenance batteries have the normal tops that you can take off to check acid levels, some look SMF but have lids hidden beneath labels.

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MikeB4

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#657978 18-Jul-2012 20:23

Before jumpstarting check with the agents for both the receiver and donor vehicles as serious damage can be done
to both vehicles Electrical control systems.

johnr

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#657981 18-Jul-2012 20:26

I did contract work for State Road side rescue and many other lease car companys and jump started enough cars to sink a battle ship

Never had an issue doing it direct to the battery

riahon

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Ultimate Geek

#657989 18-Jul-2012 20:33

johnr: I did contract work for State Road side rescue and many other lease car companys and jump started enough cars to sink a battle ship

Never had an issue doing it direct to the battery

So is it impossible or improbable?

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johnr

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#657998 18-Jul-2012 20:40

I took a car Battery off the bench charger once and I forgot to turn the charger off at the wall and it exploded, Side of the battery split open and my ears rung for a day,

Just about had to go home and change my pants and not cause of battery acid on them

jeffnz

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#658003 18-Jul-2012 21:08

we had a large commercial battery explode about 2 months ago at work. Had just come off top up charge and was being wrapped to go to one of branches and the stretch wrap managed to short across terminals and it went off like a bomb and covered a couple of guys in acid, lucky we are setup to deal with it but you can get complacent.

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AviZ

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#658038 18-Jul-2012 21:53

jumpering your car and putting it on the engine is just incase you have a poor earth, there are many earthing points on a car
so it dont matter where you put the earth.

its a very uncommon case when a battery has exploded upon a jump start.

oxnsox

1923 posts

Uber Geek

#658041 18-Jul-2012 21:57

Key thing in all this is that you should connect one lead at a time. ie: connect both ends of the +ve lead before you begin with the -ve

I've more than once seen folk connect both leads to the donor car and then have the other ends (one in each hand) touch and short, albeit briefly. Scares them white and they'll drop both leads... may also cause damage to (or stall) the donor car.

Also remove one cable completely before starting on the other for exactly the same reason.

mjb

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#658053 18-Jul-2012 22:18

riahon: I am done trying to explain what I know against what you assume. You take the risk, I really don't care.

Agreed, and no matter what you tell me, batteries (pretty much all of them) are dangerous, and care needs to be taken at all times.

Any attitude which basically boils down to "She'll be right mate" is 1) irresponsible, 2) not welcome where I work, and 3) pretty much deserves what they get.

edit: then, we're all know-it-alls here (including me), so... I'm already wrong to someone. ;)

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#658079 18-Jul-2012 22:56

Some joker swapped the red and black rubber terminal covers on the battery on one of my first cars. I had it for a couple of years then had to jump start it for the first time... fortunately no major damage to either car but I had to replace the battery on the car I was trying to jump and buy new jumper cables; and boy did it stink.

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numfarr

329 posts

Ultimate Geek

#658083 18-Jul-2012 23:01

It's pretty unlikely that it will explode, but the consequences are potentially so bad that it's worth taking a simple step to avoid. Some US statistics:

http://www-nrd.nhtsa.dot.gov/Pubs/97840.PDF
2,800 people injured by battery explosions badly enough to need hospital treatment
19% of them were jumpstarting the battery
43% of injuries were serious
72% of injuries were to the eyes, 22% to the face

avecha

209 posts

Master Geek

#658102 19-Jul-2012 00:07

KiwiNZ: Before jumpstarting check with the agents for both the receiver and donor vehicles as serious damage can be done
to both vehicles Electrical control systems.

Thats what happened to me with my Subaru.
Jump started a mate and it fried my computer. Then my car wouldn't start.

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