Connecting jump leads

[hornetrider]

Right now. I'm going to show myself to be a bit of a buffoon here, but still.

Whenever jump starting a car, I have connected the leads in the following manner - negative terminal to negative donor, then positive terminal to positive donor. I figured that it was sound practice to earth the car prior to connecting the live leads.

However, reading the manual for my new car, it states connect the positive leads first, and also to connect the negative donor to a solid earthing point on the car

So, two questions really.

1. Why do you need to connect positive first
2. Is there an issue with using the car negative battery terminal as the earthing point?

[S3_Graham]

hornetrider said:

Right now. I'm going to show myself to be a bit of a buffoon here, but still.

Whenever jump starting a car, I have connected the leads in the following manner - negative terminal to negative donor, then positive terminal to positive donor. I figured that it was sound practice to earth the car prior to connecting the live leads.

However, reading the manual for my new car, it states connect the positive leads first, and also to connect the negative donor to a solid earthing point on the car

So, two questions really.

1. Why do you need to connect positive first
2. Is there an issue with using the car negative battery terminal as the earthing point?

As far as im aware... its to do with completing the circuit in an order as to reduce the chance of sparks(completing the circuit)

So you do the positive first and last... connect it first... take it off last.

[hman]

hornetrider said:

Right now. I'm going to show myself to be a bit of a buffoon here, but still.

Whenever jump starting a car, I have connected the leads in the following manner - negative terminal to negative donor, then positive terminal to positive donor. I figured that it was sound practice to earth the car prior to connecting the live leads.

However, reading the manual for my new car, it states connect the positive leads first, and also to connect the negative donor to a solid earthing point on the car

So, two questions really.

1. Why do you need to connect positive first
2. Is there an issue with using the car negative battery terminal as the earthing point?

wiki says:

Operation of a lead-acid battery produces hydrogen gas which is flammable. Caution is needed to avoid a spark that may ignite the gas. The recommended sequence is to first connect the positive terminals of both batteries, then connect the negative post of the charged battery and make the last connection to the frame of the vehicle with the dead battery, at a location away from the battery. By not connecting the last clamp on to the dead battery, the risk of ignition is reduced. The described sequence of connections is intended to reduce the chance of accidentally shorting the good battery.

I say:

Its also best practice to use an earthing point on the engine of the car you wish to start to ensure that you minimise any power losses through the dead cars earth circuit. Obviously taking the earth jump cable to the part of the car that the starter motor etc. is directly earthed to achieves this.

[Strangely Brown]

hman said:

wiki says:

The recommended sequence is to first connect the positive terminals of both batteries, then connect the negative post of the charged battery and make the last connection to the frame of the vehicle with the dead battery, at a location away from the battery.

I say:

Its also best practice to use an earthing point on the engine of the car you wish to start to ensure that you minimise any power losses through the dead cars earth circuit.

As above... I remember it as "Boost = Both, Slave = Separate", i.e. Both cables on the boost battery and separate the cables on the slave, one on the battery and one on the chassis/engine.

Always connect one lead at a time, positive first.

Edited by Strangely Brown on Wednesday 4th February 11:23

[Rofly Lollers]

hornetrider said:

1. Why do you need to connect positive first

Because if you connect the negatives first, then if you drop the positive it could make contact with the car body and short.

[hman]

Rofly Lollers said:

hornetrider said:

1. Why do you need to connect positive first

Because if you connect the negatives first, then if you drop the positive it could make contact with the car body and short.

that as well...

[lanby]

Rofly Lollers said:

hornetrider said:

1. Why do you need to connect positive first

Because if you connect the negatives first, then if you drop the positive it could make contact with the car body and short.

and if it shorts on the bodywork it can weld itself to it,
which goes down well!

[hman]

lanby said:

Rofly Lollers said:

hornetrider said:

1. Why do you need to connect positive first

Because if you connect the negatives first, then if you drop the positive it could make contact with the car body and short.

and if it shorts on the bodywork it can weld itself to it,
which goes down well!

or the battery can explode - as 448 people a year in the US find out!