Safe way to jump start a car

[stevie_b]

Now that I only use my supra at the weekends (if that), sooner or later I'll probably need to jump start it.

 

What's the safe way of jump starting a car (not just a supra) without lunching the electrics? I thought it went something like this:

 

1) With both engines off, connect the +ve of the good battery to the +ve of the dead battery.

2) Connect the -ve of the good battery to the engine block of the car with the dead battery.

3) Start the car with the good battery.

4) Without revving the engine of the good battery, start the engine of the car with the dead battery

5) Remove -ve jump lead

6) Remove +ve jump lead.

 

Is this right? I've jump started cars before without problems, but I don't want to risk the electrics by following a sloppy procedure.

 

I searched the internet (very briefly, admitedly), and found this on the AA website:

 

1. Use the red jump lead to connect the positive terminal of the donor vehicle's good battery to the positive terminal of the flat battery.

 

2. Then use the black lead to connect the negative terminal of the good battery to a suitable earthing point on the engine or chassis of the other vehicle. This earthing point must be away from the battery and fuel system.

 

3. With both leads connected wait three minutes for the voltages to equalise before starting either engine.

 

4. Start the engine of the donor car and allow it to run for a minute then, with it still running, start the engine of the other car and leave both running at a fast idle for ten minutes. Do not remove the jump leads while the engines are running as this can cause serious damage to the electronics on either car.

 

If the jump leads get hot, then avoid a possible fire by switching off both engines and allowing the leads to cool.

 

5. Turn off the ignition on both cars and then disconnect the leads carefully in the reverse order to the way that they were connected. Be careful not to touch the clips against each other or against the car bodywork.

 

6. Start the car that had the dead battery using its own battery power. If it won't start this could indicate a more serious problem with the charging/ignition system that will need investigating by a professional.

 

 

Surely this technique wouldn't give the dead battery enough time to hold enough charge to be able to crank the car over by itself?

[Blackie]

I didnt know there was a procedure

[stevie_b]

I didnt know there was a procedure

 

Maybe there isn't, I just don't get out much!

[Swampy442]

I always put the +ve on the good battery last and take it off the good one first. Supras are 'blessed' with a dirty great lifting hook on top of the engine to put the -ve on. Not sure why you would want to equalise voltages though..

I was told many years ago not to connect 2 batteries directly together.

Good point about the leads getting hot, especially if youre using budget leads and trying to jump start a car that draws alot of current such as a diesel.

[stevie_b]

2 things in particular I'm unsure of:

 

1) should the car with the good battery be started at all?

2) assuming the answer to (1) is yes, should the car with the good battery be revved whilst the dead car is cranked?

[Benjy]

Rather than allowing your battery to go flat, if you're only using it at the weekends, why not get a cut off key? It'll take any drain away from the battery (i.e. clock etc) and it's a pretty good security device for the opportunist tea leaf.

[Ark]

I've jumped both my Supras thanks to duff jap-spec batteries.

I had the donor car running before connecting any cables to make sure the battery voltage stayed high. Connect positive first, then negative.

As long as the battery and alternator aren't totally f'ed, you only need to connect them for long enough to turn over the starter, and it'll self sustain after that. That way there's no chance of cables getting too hot.

 

The thing with not connecting directly to the battery seems a bit odd to me. Yes, it'll spark when you bring the clamp near-by, but as long as you don't piss about with it, it should be fine.

[Swampy442]

Ive always gone on how dead the battery is on the bad car, but as a rule I always run the charging car, revving does help cos the alternator ramps up to 14 or 15 volts over a certain rpm so thats gonna help. But like I said thats what Ive always done.

Or go to Halfrauds ad get a booster pack, avoid all the jump leads guff

[Ark]

2 things in particular I'm unsure of:

 

1) should the car with the good battery be started at all?

 

Yes, to keep the voltage and charge nice and stable - you don't want to wind up with two dead cars.

 

2) assuming the answer to (1) is yes, should the car with the good battery be revved whilst the dead car is cranked?

 

No.

[stevie_b]

Rather than allowing your battery to go flat, if you're only using it at the weekends, why not get a cut off key? It'll take any drain away from the battery (i.e. clock etc) and it's a pretty good security device for the opportunist tea leaf.

 

I didn't know such a device existed. Do you have one, and if so would you recommend a particular model?

[PeteA]

I think the idea behind letting the batteries equalise for a few mins is to help stop putting too much current down the jump leads - melting them.

I also reckon the AA say not to use the -ve point on the battery as its close to the +ve terminal and if you miss with the leads and melt things together you might blame them. Since any earth point is connected to the battery anyway, i dont see why you shouldnt just go straight to source?!

[keener]

The thing with not connecting directly to the battery seems a bit odd to me. Yes, it'll spark when you bring the clamp near-by, but as long as you don't piss about with it, it should be fine.

 

I used to do this but when the battery died in the middle of no where and Mr AA came to my rescue he linked the -ve to the lifting eye as described earlier. When I asked why he did this he showed me the explosive symbol on the battery and explained that they sometimes give off fumes that can explode - especially old batteries like mine! Fair enough I said, I'll connect to the lifting eye in the future too then! No risk at all of sparks.

 

I've also had issues with my stereo tripping out when I've jumped the battery. (Just disconnected the -ve, left for about an hour and it re-sets itself but a PITA none the less). Mr AA said to turn on your lights when jumping and any spike charge will go to the lights rather than stereo. No it wont blow the lights apparently.

[PeteA]

I used to do this but when the battery died in the middle of no where and Mr AA came to my rescue he linked the -ve to the lifting eye as described earlier. When I asked why he did this he showed me the explosive symbol on the battery and explained that they sometimes give off fumes that can explode - especially old batteries like mine! Fair enough I said, I'll connect to the lifting eye in the future too then! No risk at all of sparks.

 

Good call, I remember reading that now. Sealed lead acid gives off something like hydrogen. Though I would have thought the chances of there being enough to explode from connection sparks, probably about the same chances of blowing up a petrol station with your mobile, but doesnt seem worth risking it

[creative]

I used to do this but when the battery died in the middle of no where and Mr AA came to my rescue he linked the -ve to the lifting eye as described earlier. When I asked why he did this he showed me the explosive symbol on the battery and explained that they sometimes give off fumes that can explode - especially old batteries like mine! Fair enough I said, I'll connect to the lifting eye in the future too then! No risk at all of sparks.

 

 

we have a winner!

 

I have been there when a battery has exploded when the charging pack slipped off the neg terminal on a battery and it ignited.... not an experience I want to re enact!

[Fire148]

A few weeks ago I had to jump start a Supra, and the guy who was 'helping' with his jeep connected the leads around the wrong way at his end.

 

The main fuse blew on the supra ... 120A fuse I think ...

 

I have never seen anyone do this until now, and I was torn between laughing and crying ! His jeep seemed fine, but FFS !

[garethr]

I always put the +ve on the good battery last and take it off the good one first.

Wrong, Craig

 

If you connect the -ve to the car with the duff battery first, then you'll have a short if you drop the +ve jump lead into the engine compartment.

1. +ve good

2. +ve duff

3. -ve good

4. -ve duff (not directly to the battery)

 

Remove in reverse order.

[stevie_b]

To summarise:

 

1) Connect lead to +ve on donor battery

2) Connect lead to +ve on duff battery

3) Connect lead to -ve on donor battery

4) Connect lead to -ve on duff engine block (or any other beefy-looking metal part of the engine or chassis), not the battery terminal itself

5) Start the donor car

6) Wait a couple of minutes to allow voltages to settle down (not sure if this is necessary, but no harm in doing it)

7) Start the car with the duff battery, without revving the donor car

7a) Optional: To be uber-safe to the cars' electronics, allow the engines to run for 10 mins at this point and then turn off both engines.

8) Disconnect the jump lead clamps in reverse order of connecting them.

 

This differs a bit from what some poeple have said in this thread, but I'm trying to record the safest way of doing it.

 

Mods, if this sounds about right, maybe it could be saved as a FAQ or HowTo or something.