Training Titbits .. Jumpstarting

[james chalkley]

The latest instalment from the SE4x4R training team.

And now with added video https://www.youtube.com/watch?v=BJWGCnghf6o

Jump leads are a handy way of recharging a flat battery, but they can cause real damage to both cars and people if they’re not used properly.

Important safety information
Batteries produce flammable gases, so:
never try to jump start a battery that looks damaged or is leaking
don’t use jump leads that are damaged
stop using the jump leads if they get hot. Switch off both engines and allow the leads to cool to avoid a possible fire
never smoke or allow naked flames anywhere near either battery
don’t let any metal objects come in contact with the cars’ batteries, as these could cause a spark and possibly make the battery explode. That includes rings, necklaces, watch straps, hand tools, clips, stray wires etc
Don't remove the jump leads while the cars’ engines are running. This can cause serious damage to the cars’ electronics
Before you start, remove any loose-fitting clothing – like a scarf or tie – as these could get caught up in the moving engine parts
A step-by-step guide
Find someone with a car who’s happy to help. Their car must have a fully charged battery with the same voltage as yours (usually 12 volts)
Park both cars so their batteries are within easy reach of one another (without the cars actually touching). Keep the handbrakes on and the ignitions off
Use the red jump lead to connect the working battery’s positive (+) terminal to the flat battery’s positive (+) terminal
Take the black jump lead and attach it to the negative (-) terminal on the working battery. Then attach the other end to an earthing point (unpainted metal on the engine block or chassis) well away from the flat battery and fuel system
Keep both engines off and wait for three minutes, then start the working car’s engine and let it run for a minute
Start your car
Leave both cars to idle, at a fast pace, for around 10 minutes
Turn off both cars’ engines and carefully disconnect the leads in the reverse order to the way they were connected (i.e. remove the black lead from your car first and finish with the red lead from the other car). Make sure the leads don’t touch one another, or either car, as you remove them
Restart your car
If your car won’t start there’s probably a more serious problem requiring professional help

[Jerry G]

Quote (partial) 'Don't disconnect while engine running. Can seriously damage cars electronics.'
Yet utube video shows just that! Explain.

[Stephen Marquis]

Originally Posted by JerryG

Quote (partial) 'Don't disconnect while engine running. Can seriously damage cars electronics.'
Yet utube video shows just that! Explain.

If you switch off to disconnect jump leads, there is a pretty good chance the dud vehicle will not restart as it will not have gained enough charge to restart yet.

Both vehicles should also switch off unnecessary electrical loads, heated screens, sidelights only etc during the process,and the dud vehicle should maintain minimum necessary electrical load until it is certain there is enough charge stored to enable restarting

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[Gordon Brown]

Indeed - the instruction to switch-off to disconnect the leads goes against the training I've had previously, not to mention the instruction for undertaking a jump-start in my vehicle's handbook.

I'd be interested to hear the rationale / provenance of that particular approach.

[James Addy]

I agree, in that the way I was taught was to start engine and leave running whilst carefully removing the leads.

And my guess is that any 'official' training, may say turn off engines before disconnecting to try and safeguard any shorting or Engine Management Unit issues (But can't see how it would avoid any of that if the engines were off - your dealing with potentially raw electricity, so be careful, be safe, and keep the leads apart at both ends at all times until nowhere near vehicles and/or batteries)

Regards James

[Jerry G]

Well you could switch off the donor vehicle to halve the perceived problem. But actually, whether the engines are running or not, you still have live 12+ volts at both ends with no short circuit protection!
So as the previous poster says, keep leads apart and clear of everything.
The donor should start again as it was full up before the jump start.
Put some electrical load on the 'jumped' vehicle to stabilise the voltage, not too much, before disconnecting.