Jump starting procedure

[donkmeister]

I'm contemplating a jump between two modern cars (to avoid having to wait hours on the charger for the car I need to shift!)

As it's not something I've ever needed to do before I checked the procedure and everyone says to connect the leads with ignition off on both cars, leave for a bit, then start, run for a while, then turn off and disconnect.

Anyone know why it isn't "leave good car running and connect, thus allowing the alternator to take the load instead of the battery, then disconnect with engines running so you aren't trying to restart with a still quite flat battery"? Either way you are holding energised leads with somewhere between 12 and 15 volts, so can't be for personal safety.

As it's connecting the two batteries in parallel, I don't see how it protects anything to do it with engine off instead of on. Has anyone fried a car through connecting/disconnecting leads with the engine running?

[Jordie Barretts sock]

For decades I've always connected the leads to the running car with the engine running, then connected the leads to the flat battery. Leave a bit to get some charge into it, then start the flat car and then disconnect the leads. Never had an issue.

A Romanian friend told me a great bodge, not sure how healthy it is for the alternator, but it does work.
Get a fully charged battery, take the terminals off the flat battery in the car and touch them to the good battery (don't tighten the clamps, basically) Start the car and then reattach the clamps to the flat battery in the car. Obviously for a moment the car is running and not attached to a battery, so not sure if that's healthy for it, but it gets the car started!

[hellorent]

I've always had donor car engine running & connect pos lead 1st then neg lead, never had a problem
doing it that way, oh DON'T leave keys in ign of sick car as it may well lock when you connect
jump leads up.

[GreenV8S]

hellorent said:

I've always had donor car engine running & connect pos lead 1st then neg lead, never had a problem
doing it that way,

Same here. Extra brownie points for making the last negative connection to a vehicle ground point instead of directly to the battery so any arc is not close to the battery.

I assume the 'engine off' approach is designed to minimise the risk of frying electronics due to a voltage spike. I don't know how much of a problem that is because I'm not jump starting engines every day, but I'd expect modern vehicles to be tolerant of this sort of thing.

[Pit Pony]

My process:

Both cars off.

Connect earth terminals with black lead

Connect live terminals with red lead

Start "good" car.

Start "bad" car

The only time this didn't work was when the crank position sensor had failed on my 3.2 omega.

Remove red lead

Remove black lead.

Drive good car back onto drive. Pop keys through letter box so wife has her car back.

Get in bad car and drive to work, with leads in footwell, just in case you need to hijack a work colleague at the end of the day to help you get home.

When you get home, put battery on charge overnight and hope you don't have to fork out for a new battery.

3 weeks later. Buy new battery.

[normalbloke]

I now refuse to jump start a dead vehicle, or allow anyone to jump from my vehicle, due to the increased risk of electrical damage to modern fickle vehicles. I have a decent sized Noco booster that has not failed to start anything yet, and avoids the risk.

[Jordie Barretts sock]

And rhe Noco is different to a jump start, how?

[Super Sonic]

Jordie Barretts sock said:

And rhe Noco is different to a jump start, how?

Because it's not risking electrical damage to normalblokes car.

[E-bmw]

Super Sonic said:

Jordie Barretts sock said:

And rhe Noco is different to a jump start, how?

Because it's not risking electrical damage to normalblokes car.

Unless his is the car being jumped.

[Ken_Code]

Jordie Barretts sock said:

And rhe Noco is different to a jump start, how?

An idiot who I used to know “jump started” another friend’s car by connecting the positive on the working car to Earth on the flat-ish one and vice-versa.

Nothing went on fire, but the melted cables and bumper added to the cost of two new batteries.

A Noco boost helps to reduce the risk of this.

[Pit Pony]

Ken_Code said:

An idiot who I used to know “jump started” another friend’s car by connecting the positive on the working car to Earth on the flat-ish one and vice-versa.

Nothing went on fire, but the melted cables and bumper added to the cost of two new batteries.

A Noco boost helps to reduce the risk of this.

Or you could just learn how to do it correctly in the first place.

[Ken_Code]

Pit Pony said:

Or you could just learn how to do it correctly in the first place.

What a stupid suggestion, I already know how to do it properly.

[Chris32345]

Jordie Barretts sock said:

For decades I've always connected the leads to the running car with the engine running, then connected the leads to the flat battery. Leave a bit to get some charge into it, then start the flat car and then disconnect the leads. Never had an issue.

A Romanian friend told me a great bodge, not sure how healthy it is for the alternator, but it does work.
Get a fully charged battery, take the terminals off the flat battery in the car and touch them to the good battery (don't tighten the clamps, basically) Start the car and then reattach the clamps to the flat battery in the car. Obviously for a moment the car is running and not attached to a battery, so not sure if that's healthy for it, but it gets the car started!

If you have a honda absolutely do not try this or even leave your keys in the ignition while disconnecting a battery it often ruins the imobliser

[Jordie Barretts sock]

I did think it was a bit iffy!

Worked on an old Peugeot 407 though!

[Pit Pony]

Ken_Code said:

Pit Pony said:

Or you could just learn how to do it correctly in the first place.

What a stupid suggestion, I already know how to do it properly.

When I said You. I meant the "Royal you". As in your idiot friend, so not actually you.

[donkmeister]

The good news is that in the time it took to post this, then go and buy jump leads, my charger stuffed enough electrons into the battery that the car started just fine.

Now I've got the leads, I think if it happens again and I don't want to wait for the charger I'll jump from a known good battery, disconnected from its car.