Stoopid battery question

peasant

Here's one for the experts ...can you jump-start a car by connecting the jump leads to the + and - wires only (i.e just the cables, no battery connected) or would that do damage due to overvoltage or whatever ?

I honestly don't know

Eric Cartman

so the 'jumped' car has no battery and your just connecting the terminals to the 'jumper' cars battery

If you got jumper cables with a large enough gauge wire it is possible, but with all the electronic systems in cars now chances are the car would die again after you disconnected the 'jumper' cars battery

JoeySully

It will start and run but will most likely die after you disconnect leads.

However! Old diesel engines will run without a battery connected.

whizbang

disconnecting a battery with engine running can be fatal for electronics.

you can jump start any way you like, but if you cant disconnect the leads, then whats the point.

peasant

whizbang wrote: »

... but if you cant disconnect the leads, then whats the point.

Let's just say you wanted to start the engine on a prospective purchase where the battery is damaged beyond repair or charging (or missing altogether)

coylemj

peasant wrote: »

Here's one for the experts ...can you jump-start a car by connecting the jump leads to the + and - wires only (i.e just the cables, no battery connected) or would that do damage due to overvoltage or whatever ?

It's not clear exactly what you're proposing to do. In a normal jump start scenario, you have a 'good' battery, typically in a car parked alongside the car with the dud battery. You run the engine in the car with the good battery, then you use the jump leads to connect + to + and - to - and then you attempt to start the car with the flat battery.

In that scenario, the batteries are connected in parallel so the voltage is still 12V and the stronger battery will be used to start the engine.

If you use one single cable and connect it to the + and - terminals on a battery, you will short the circuit and get a large flash of sparks, even in a flat battery. You also risk the battery exploding and you will certainly destroy it if you leave the terminals connected to each other.

If you connect the two cables to + and - on a battery with no good battery at the other end of the leads as you seem to be suggesting, you will achieve nothing and the car with the flat battery will not start.

slimjimmc

I guess you'd want to make very sure the +ve lead doesn't short against the -ve lead or any metallic part of the car after you disconnect otherwise you might damage your alternator.

peasant

coylemj wrote: »

It's not clear exactly what you're proposing to do.

Quite simple really ...perform a jump start as normal where the car on the receiving end has no battery, so the jump leads would be attached to the connectors only.

This is just a theoretical question.

whizbang

cant see any problems in that case, Peasant, but prob the best thing is to beg, buy, steal, a spare battery.
Long High quality leads will allow you to put the spare in the passenger window, and take a nice leisurely test drive.

I've started as car it in the past with a battery in situ but so dead that it was totally useless (caveat: I dont know if this applies to modern electronic setup). The only problem is that it you stop somewhere or cut out, you need to jump start again. As somebody mentioned above, if the leads are not connected to the battery you need to be sure they dont touch the bodywork or you will short everything.

Mar4ix

Cant see any problems start that way, just after start, put " + " lead in to multiple bags, and rubber glow, to make sure, it wont contact cars body or any metallic cars part. .

I think it is clear to everyone, that car is running from alternator, .. battery need just for starting car, after car is started, all electrical power taken from alternator, also alternator charging battery.