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My neighbours car wouldn't start this morning and as it has been unused on her drive for around 4 months I suspect that it might be the battery.

I said I would happlily jump start it for her but I am not sure how to do it.

Do I connect the red lead to the positive on my battery and the positive on her battery

Connect the black lead to the negative on my battery and the negative on her battery

Start my car

Rev my car a little

Get her to start her car

 

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I was always told to put the headlights on first incase of surge reducing the risk of damaging ecu or modules, put positive lead on both then negative my car has always been running anyway when I connect leads just be mindful of moving parts

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8 minutes ago, ilovemyheckler said:

My neighbours car wouldn't start this morning and as it has been unused on her drive for around 4 months I suspect that it might be the battery.

I said I would happlily jump start it for her but I am not sure how to do it.

Do I connect the red lead to the positive on my battery and the positive on her battery

Connect the black lead to the negative on my battery and the negative on her battery

Start my car

Rev my car a little

Get her to start her car

 

in that order.........always connectbthe negertive last............well done:good:

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Totally off topic but what ever you do DO NOT TRY AND BUMP START A CAR unless you fancy a broken timing belt, a workmate also works for the RAC & he was telling me he has lost count of people with dead batteries trying to bump start their cars resulting in a snapped belt.

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1 hour ago, London Best said:

Timing BELTS. Real progress in engine design...........NOT.

Actually yes.  But since superseded.  

Back on topic:

Ideally, always connect the negative on the dead vehicle on the body/engine.  This is because the flow of electrons is actually from negative to positive. You want to provide the best possible path from the healthy vehicle's battery terminals to the starter motor (and back again), WITHOUT getting diverted via the dead battery (as far as possible).

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Connect the red (positive +) terminals between each car.  Then use the black lead to connect between some part of the chassis on each car (rescue car first, then flat one).  You can usually find a suitable spot under the bonnet like an engine mount.  You'll often get a little spark from the black croc clip as you touch it onto the stricken car's chassis, which is a sign you've got a circuit..  A 12v DC circuit in a vehicle is "earthed" or "grounded" to the chassis, so the circuit will be made when you connect each chassis to each other.

Found this, which is not a perfect explanation but is a start:

Quote

During jump-starting, we connect the boosting battery to ground rather than to the dead battery's - terminal for the simple reason that this provides a more direct return path to the good battery which is powering the dead car: the return current does not have to travel through the dead battery's minus terminal hookup cable and then to the jumper cable, but can go directly from the chassis ground to the jumper cable.

A more direct return path allows for better current flow and less voltage drop, like plugging a big appliance directly into an outlet, rather than via an extension cord.

In case you're also wondering why the plus jumper connections are made first, then the minuses. This is because there is no harm done if you leave the minus jumper dangling in the chassis of the car. Anything it accidentally touches is likely to be ground. If you connect both alligator clips on one end before connecting the other end, the other end is now live and you can accidentally touch the clips together to create a short circuit. If you connect the minuses/grounds first and then go to connect one of the pluses, you can create a short circuit, because the opposite side plus is probably dangling and touching something that is grounded.

 

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Was at a petrol station yesterday and the guy in front of me opened his boot took a battery and jump leads to the front of his car and jump started his car while still parked at the pump. Dodgy thing to be doing!

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On 30/01/2021 at 15:43, blackbird said:

Totally off topic but what ever you do DO NOT TRY AND BUMP START A CAR unless you fancy a broken timing belt, a workmate also works for the RAC & he was telling me he has lost count of people with dead batteries trying to bump start their cars resulting in a snapped belt.

Anyone care to explain how a bump start could possibly damage a timing belt? Surely it's the case that whatever way the engine is started it's always the crankshaft that drives the belt so a bump start doesn't do anything the starter motor doesn't do.

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I was surprised about the timing belt, but it could well be right. When you turn the starter key it turns the engine over relatively slowly. If you tow or bump start, I suspect there is far more instant pressure.

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2 hours ago, Westward said:

Anyone care to explain how a bump start could possibly damage a timing belt? Surely it's the case that whatever way the engine is started it's always the crankshaft that drives the belt so a bump start doesn't do anything the starter motor doesn't do.

I've never heard of a belt letting go when bump starting but I have heard of ford transit's camchain jumping a tooth.

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