Dead Battery

Richard53

Mankysteve wrote: »

3. If you undo The negative first you don't get sparks and if renders the positive cable safe.

You can get sparks from either terminal when you break the connection. There's nothing magic about the negative. The advice to connect the negative last and disconnect first is because you can connect the negative cable to a part of the engine (like a lifting eye) well away from the battery, which means that any spark is well away from any H the battery may be giving off.

Connecting directly to the engine metal is also better for starting purposes as it bypasses the battery earth lead, which on an old car is often corroded and with poor connections, and gives the full power of the slave battery to the starter motor.

[Deleted User]

Richard53 wrote: »

The advice to connect the negative last and disconnect first is because you can connect the negative cable to a part of the engine (like a lifting eye) well away from the battery, which means that any spark is well away from any H the battery may be giving off.

The reason for connecting positive first is because it reduces the risk of an accidental short circuit.

With +ve first, if you drop the +ve lead there's no short because the negative isn't yet connected, and if you drop the -ve there's no short if it lands on the bodywork etc because that's where it was going anyway.

If the -ve is connected first, and then you drop the +ve onto the bodywork there'll be fireworks.

(Note that it's the live which goes on before the earth, irrespective of whether you have +ve or -ve earth.)

Richard53

That as well

Thanks.

TrickyWicky

Bedsit_Bob wrote: »

Not directly related to the problem the OP has right now, but for anyone who regularly leaves a car unused for weeks/months, one of these isn't a bad idea.

It is a bad idea if you have a car with an immobiliser that disables the cig lighter socket.. why? because it won't take any charge and you won't even realise but will waste money buying it.

Anyone ever considering a charger that plugs into the fag socket should forget it unless it's something pre 1990 without an immobilier.

Richard53

TrickyWicky wrote: »

Anyone ever considering a charger that plugs into the fag socket should forget it unless it's something pre 1990 without an immobilier.

Ford Mondeo, 2006, has immobiliser. The lighter socket between the front seats is permanently live, so a solar charger would work fine.

arcon5

The Mondeo (like many cars I suspect) has a fuse that can be moved to make it live when the ignition is on or all the time.

gabitzul

arcon5 wrote: »

The Mondeo (like many cars I suspect) has a fuse that can be moved to make it live when the ignition is on or all the time.

Most of the modern Fords are like that in fact. I had a Focus MK1 and now a MK2 one and both have always live fag lighter sockets.

Uniscots97

The battery charger hasn't arrived yet, so I'm going to try it again. Its an older car (97) with an immobiliser. I don't want to remove the battery, I just want to get my car going again!

IamNotAllowedToUseMyName

Uniscots97 wrote: »

The battery charger hasn't arrived yet, so I'm going to try it again. Its an older car (97) with an immobiliser. I don't want to remove the battery, I just want to get my car going again!

Just to be clear, on an absolutely flat battery, I would expect you to connect up the other car, run it for a little while, say 5 minutes, to get some basic level of power into the other battery, go for a start, and then drive the car for a significant amount of time at a reasonable pace, at least 30 minutes, with no accessories on.

I've jump started a Golf many times due to lack of use and the battery survived the experience fine, but if the battery is several years old then it is quite possible it is worn out. I have two old cars, the Merc, which has a very high capacity battery is on its third battery, each lasting about 7 years, the Golf is on its second battery, the first lasting about 10 years. The Merc's last failure was due to lack of voltage where a cell had failed - basically it was unable to produce the correct voltage so the electronics on the car would not work, even though it would charge up.

TrickyWicky

Uniscots97 wrote: »

The battery charger hasn't arrived yet, so I'm going to try it again. Its an older car (97) with an immobiliser. I don't want to remove the battery, I just want to get my car going again!

I wish you luck then because it sounds to me like you've a duff battery, alternator or both as many of us have told you.

You came here and asked for advice. We've given it, you've ignored it. Mind me asking why?

It's all well and good getting it "going again" but what happens the next time? and the next time? and the next time?

You need to check your alternator. Get a multimeter and with the engine running, check the voltage of the battery. If it's 13-14v then your alternator is fine and your battery is defective. If it's below that then the alternator is not functioning correctly and you've probably knackered your battery relying on it so much with no recharges.