Jump starting a car

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nate

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#106150 18-Jul-2012 17:36

When it comes to car, I'm hopeless. My complete car knowledge is: it has two pedals, one steering wheel and needs gas to go.

If you are jump starting a car I know you attach positive to positive. The one I'm confused about is, is it negative to negative OR negative to another part of the other car's body.

It seems everyone I talk to has different opinions of what is right. Keen to hear thoughts from here...

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#657871 18-Jul-2012 17:38

I'm also not a car person but I've done negative to negative and nothing exploded :)

billgates

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#657875 18-Jul-2012 17:41

red to red. black to black. make sure you start ignition on the good car before you connect the cables to the dead car

Do whatever you want to do man.

Phexx

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#657876 18-Jul-2012 17:43

Negative to negative terminal is usually what we do but I have talked to motorsport mechanics and they personally recommend this:

Good car = negative to battery
Bad car= negative to ground point on car, the alternator is a good place

Always make sure to read the owners manual, an AA guy decided to hook up the negative to the negative on the battery. Next minute there is smoke coming out of his bonnet (bad car was an rx-8).

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#657880 18-Jul-2012 17:44

- to the - on battery is fine

ubergeeknz

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#657892 18-Jul-2012 17:56

nate:
If you are jump starting a car I know you attach positive to positive. The one I'm confused about is, is it negative to negative OR negative to another part of the other car's body.

This is how I do it:

Donor car: car with good battery
Recipient car: car with dead battery because you left the lights on, you idiot :)

Turn off all accessories in both cars. Start the donor car and let it run for a few minutes to charge its own battery. If it was already running, then keep it running. The shock of charging a battery that's just started an engine + the dead battery will strain the alternator even more.

Connect red wire to Recipient battery + terminal, and connect the other end to the donor + terminal. Make sure they're secure!

Connect black wire to Recipient engine block (usually there's a hoisting hook sticking out which is handy for this purpose). This is because the block is where the starter is earthed to, so it will give the highest voltage to the starter possible. If you can't find anywhere, the - terminal will work, just not quite as well.

Now connect the other end to the donor car engine block or battery - terminal. The engine block is also where the alternator is earthed to. There will be sparks, don't be afraid, just secure it well and wiggle it on the metal to get a clean connection. At this point, the revs will likely drop a little on the donor car as it takes up the strain of charging the dead recipient battery.

On the donor car, take the revs up a little (about 1500rpm) so that the alternator runs at full efficiency. Run it for a minute or two to get some charge into the recipient battery.

Start recipient car.

Disconnect donor -, and recipient -, drop them to the ground. Then donor + terminal and recipient + terminal (in that order). Note that dropping the - connections first decreases your chance of shorting one of the + ends of the cable to one of the car bodies accidentally, and melting something.

Now I am no auto electrician, but this works well in most circumstances, unless your recipient battery is completely toast. In that case your only option is to replace it.

gregmcc

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#657913 18-Jul-2012 18:36

ubergeeknz:
nate:
If you are jump starting a car I know you attach positive to positive. The one I'm confused about is, is it negative to negative OR negative to another part of the other car's body.

This is how I do it:

Donor car: car with good battery
Recipient car: car with dead battery because you left the lights on, you idiot :)

Turn off all accessories in both cars. Start the donor car and let it run for a few minutes to charge its own battery. If it was already running, then keep it running. The shock of charging a battery that's just started an engine + the dead battery will strain the alternator even more.

Connect red wire to Recipient battery + terminal, and connect the other end to the donor + terminal. Make sure they're secure!

Connect black wire to Recipient engine block (usually there's a hoisting hook sticking out which is handy for this purpose). This is because the block is where the starter is earthed to, so it will give the highest voltage to the starter possible. If you can't find anywhere, the - terminal will work, just not quite as well.

Now connect the other end to the donor car engine block or battery - terminal. The engine block is also where the alternator is earthed to. There will be sparks, don't be afraid, just secure it well and wiggle it on the metal to get a clean connection. At this point, the revs will likely drop a little on the donor car as it takes up the strain of charging the dead recipient battery.

On the donor car, take the revs up a little (about 1500rpm) so that the alternator runs at full efficiency. Run it for a minute or two to get some charge into the recipient battery.

Start recipient car.

Disconnect donor -, and recipient -, drop them to the ground. Then donor + terminal and recipient + terminal (in that order). Note that dropping the - connections first decreases your chance of shorting one of the + ends of the cable to one of the car bodies accidentally, and melting something.

Now I am no auto electrician, but this works well in most circumstances, unless your recipient battery is completely toast. In that case your only option is to replace it.

Electrically there is no real benefit connecting the - jumper cable to either the engine block/lifting point or right to the - terminal on the flat battery.

All it takes is a bit of common sense, a little thought before hand to identify the correct battery terminals and you can't really screw it up....unless you're already brain dead.....

johnr

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#657914 18-Jul-2012 18:38

+1 to what Greg advises

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riahon

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#657920 18-Jul-2012 18:46

If an engine lifting bracket is handy I will go there. Apart from the risk of battery exploding, which is slight, attaching to the engine means the path is closer to the starter motor as poor earths add extra resistance.

gregmcc

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#657927 18-Jul-2012 18:59

riahon: If an engine lifting bracket is handy I will go there. Apart from the risk of battery exploding, which is slight, attaching to the engine means the path is closer to the starter motor as poor earths add extra resistance.

Just how much resistance between the starter motor earth and the battery - do you think there is? I would be more worried about poor resistance where ever you connect to the lifting point/engine block (paint/rust/grease etc) at least at the battery terminals the clips on the jumper leads will bite in to the soft battery terminals giving a good connection

mjb

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#657930 18-Jul-2012 19:05

One of the main reasons for not connecting the last connection directly to the battery is so that any sparks/arcing (however unlikely it is for that to happen, but can, if the dead battery is really dead, since there will be a large amount of current flowing) don't happen near a charging battery - which releases hydrogen - a highly flammable gas.

You should also wear safety glasses when you do this.

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gregmcc

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#657943 18-Jul-2012 19:16

mjb: One of the main reasons for not connecting the last connection directly to the battery is so that any sparks/arcing (however unlikely it is for that to happen, but can, if the dead battery is really dead, since there will be a large amount of current flowing) don't happen near a charging battery - which releases hydrogen - a highly flammable gas.

You should also wear safety glasses when you do this.

If the battery is actually flat then there wont be any hydrogen gas, there will be hydrogen gas present druing charging, but that won't happen until the jumper cables are actually connected, and there won't be enough hydrogen generated in the instant it takes to connect the jumper cable. Even if there was enough hydrogen gas present (for what ever reason) conncting the last jumper cable to another earth point around the engine means that you are most likely not more than a meter away and won't make any difference in regards to the possibility of a hydrogen explosion

riahon

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#657945 18-Jul-2012 19:19

gregmcc:
riahon: If an engine lifting bracket is handy I will go there. Apart from the risk of battery exploding, which is slight, attaching to the engine means the path is closer to the starter motor as poor earths add extra resistance.

Just how much resistance between the starter motor earth and the battery - do you think there is? I would be more worried about poor resistance where ever you connect to the lifting point/engine block (paint/rust/grease etc) at least at the battery terminals the clips on the jumper leads will bite in to the soft battery terminals giving a good connection

Batteries are usually mounted on inner guard. Often they have a strap from battery to body then, body to engine. When you clamp a jump starter clamp directly to a terminal you don't actually 'touch' the soft terminal. It is the hard terminal clamp. It is what we were taught to do at mechanics school years ago. There was also an 'order' to add the jumper leads as well to minimise risk to car and explosion.

riahon

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#657949 18-Jul-2012 19:28

gregmcc:
mjb: One of the main reasons for not connecting the last connection directly to the battery is so that any sparks/arcing (however unlikely it is for that to happen, but can, if the dead battery is really dead, since there will be a large amount of current flowing) don't happen near a charging battery - which releases hydrogen - a highly flammable gas.

You should also wear safety glasses when you do this.

If the battery is actually flat then there wont be any hydrogen gas, there will be hydrogen gas present druing charging, but that won't happen until the jumper cables are actually connected, and there won't be enough hydrogen generated in the instant it takes to connect the jumper cable. Even if there was enough hydrogen gas present (for what ever reason) conncting the last jumper cable to another earth point around the engine means that you are most likely not more than a meter away and won't make any difference in regards to the possibility of a hydrogen explosion

If a battery is flat it could be that it is out of water, and that could be because the alternator is overcharging - therefore risk of gas. If you had to strike a match, would you rather do it right next to a petrol tank or a metre away. (metre - to carry on from another thread - not meter). The theory is that gas is being produced from cells mere centimetres away from the terminals so a spark could cause an explosion however the gas is quickly dissipated when it drifts beyond that.

gregmcc

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#657954 18-Jul-2012 19:38

riahon:
gregmcc:
mjb: One of the main reasons for not connecting the last connection directly to the battery is so that any sparks/arcing (however unlikely it is for that to happen, but can, if the dead battery is really dead, since there will be a large amount of current flowing) don't happen near a charging battery - which releases hydrogen - a highly flammable gas.

You should also wear safety glasses when you do this.

If the battery is actually flat then there wont be any hydrogen gas, there will be hydrogen gas present druing charging, but that won't happen until the jumper cables are actually connected, and there won't be enough hydrogen generated in the instant it takes to connect the jumper cable. Even if there was enough hydrogen gas present (for what ever reason) conncting the last jumper cable to another earth point around the engine means that you are most likely not more than a meter away and won't make any difference in regards to the possibility of a hydrogen explosion

If a battery is flat it could be that it is out of water, and that could be because the alternator is overcharging - therefore risk of gas. If you had to strike a match, would you rather do it right next to a petrol tank or a metre away. (metre - to carry on from another thread - not meter). The theory is that gas is being produced from cells mere centimetres away from the terminals so a spark could cause an explosion however the gas is quickly dissipated when it drifts beyond that.

If it's out of water then there won't be any hydrogen gas, as the gas is a by product of the charging process and is seperation of oxygen and hydrogen from the water in the battery.

when was the last time you heard of a hydrogen explosion as a result of a car been jump started? take a look at any modern car battery, they are a completly sealed unit, nothing in or out except electrons.

tardtasticx

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#657958 18-Jul-2012 19:46

Every time my car has died, I usually sit there for about 10 minutes wondering what to do, usually end up calling whoever lives closest to where I am, if that fails, I call daddy. Lol. Nearly all my friends know how, but not me. Should probably learn. I have changed a tire before though! I was very impressed with myself that day :P

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