Very basic question about jump starting 2008 V70

[Tannaton]

Its really simple...

Have the engine running on the donor car.

Connect the +ve terminal of the donor car battery to the -ve terminal of the car needing to be jumped.

Then connect the +ve terminals in the same way.

Ideally, leave it like that for 5-10 mins, if the battery in the stranded car is healthy (albeit discharges) it should charge quickly.

Start the car... once running remove the jump leads as soon as you can. But no need to run.

There is no danger of a surge or voltage spike as the maximum potential across a healthy lead acid battery is 14.something volts.

It's best in this case to connect directly battery to battery as the soft lead battery terminals are best for conduction with crocodile clips and high amps. As you are just jump starting, you won't throw the battery monitor out.

There is no need to leave light on or anything, just start the car in the normal way.

[Tannaton]

THAT should say -ve to -ve, then +ve to +ve, but for some reason it wont let me edit it!

[Tatsfield]

When I read your first of two posts, I thought something was seriously wrong!

[Discombobulated]

Originally Posted by Tannaton

Its really simple...

Have the engine running on the donor car.

Connect the +ve terminal of the donor car battery to the -ve terminal of the car needing to be jumped.

Then connect the +ve terminals in the same way.

Ideally, leave it like that for 5-10 mins, if the battery in the stranded car is healthy (albeit discharges) it should charge quickly.

Start the car... once running remove the jump leads as soon as you can. But no need to run.

There is no danger of a surge or voltage spike as the maximum potential across a healthy lead acid battery is 14.something volts.

It's best in this case to connect directly battery to battery as the soft lead battery terminals are best for conduction with crocodile clips and high amps. As you are just jump starting, you won't throw the battery monitor out.

There is no need to leave light on or anything, just start the car in the normal way.

I would love to know who taught you this!

https://youtu.be/dJMLD40bi-A

This video doesn’t mention putting the headlights on like I was taught to soften the spike but does say not to have the engine running on the donor vehicle when connecting the leads. Putting ‘14.something’ volts straight into an electrical system that is running at a lot less than 12 volts. It also says to connect the negative lead away from the battery.

Please type ‘jump starting voltage spike’ into google, or better still, leave the jump starting to proffesionals!

[Discombobulated]

^^ I meant to say putting 14.something volts into a system that’s running a lot less than that is not a good idea.

Luke

[Tannaton]

14.6 volts is the saturation voltage of a lead acid battery - i.e. the voltage applied to every electrical component in your car when the engine is running and the alternator is charging. Applying 14.6 volts from a fully charged donor system will do no harm whatsoever.

Leaving the headlights on is a pointless drain on the electrical system and an utter old wife's tail - especially given that probably 50% or more of us now have HID or LED headlights which are electronically regulated. It's flat earth society level - by a margin of at least 1000% the voltage regulator in the system is the battery of the donor car.

The only reason many sources say not to connect the -ve lead directly to the battery is to avoid sparks near the battery, however from an electrical point of view it is the safest central earthing point, attach to the wrong place and you might have a floating earth potential meaning different systems are supplied at different voltages. You wouldn't dream of trying to connect the +ve jump lead to the back of the alternator or starter, and most booster battery packs advise connecting directly to the battery as they is the most efficient method of connecting high current power supplies.

As regards to "leave jump starting to the professionals" - I partake in this forum to talk about cars, not people, my life is sufficiently enriched that I don't feel the need to do that...

[Discombobulated]

Originally Posted by Tannaton

Applying 14.6 volts from a fully charged donor system will do no harm whatsoever.

Tannaton, could you please explain what a voltage spike is?

I’m not saying any vehicle will be harmed by having 14.6 volts through it, it’s the sudden difference in voltage that does the harm. Putting the headlights on can absorb some of this, and having the donor vehicle switched off will also help as the voltage in that battery would be ~12.6 volts when switched off rather than 14.6 when running.

I’m really not sure where you were taught your method of jump starting, but my method was from a breakdown assistance company called Mondial, they had breakdown contracts with Aston Martin, Mercedes, BMW, Bentley, JLR and others.

I have used my method to jump start a dead Nissan GTR from an Aston Martin DB9 that was parked at the side of it, both cars were in a customers garage with no access for my lorry and it worked fine.

I guess on here there’s no basic question, even when it something as simple as a jump start

Luke

[Tannaton]

Originally Posted by Discombobulated

Tannaton, could you please explain what a voltage spike is?

I’m not saying any vehicle will be harmed by having 14.6 volts through it, it’s the sudden difference in voltage that does the harm. Putting the headlights on can absorb some of this, and having the donor vehicle switched off will also help as the voltage in that battery would be ~12.6 volts when switched off rather than 14.6 when running.

I’m really not sure where you were taught your method of jump starting, but my method was from a breakdown assistance company called Mondial, they had breakdown contracts with Aston Martin, Mercedes, BMW, Bentley, JLR and others.

I have used my method to jump start a dead Nissan GTR from an Aston Martin DB9 that was parked at the side of it, both cars were in a customers garage with no access for my lorry and it worked fine.

I guess on here there’s no basic question, even when it something as simple as a jump start

Luke

Voltage Spike = A significant increase in measured voltage applied over a very short period of time (i.e. 10x the voltage for 10 nano seconds?).

Opposed to a voltage surge which would be a proportionately smaller increase in voltage over a long period of time (i.e. +10% for 3 seconds).

[Discombobulated]

Originally Posted by Tannaton

Voltage Spike = A significant increase in measured voltage applied over a very short period of time (i.e. 10x the voltage for 10 nano seconds?).

Opposed to a voltage surge which would be a proportionately smaller increase in voltage over a long period of time (i.e. +10% for 3 seconds).

And you got that information from where?

[Tannaton]

That's my recollection from when I first studied the IEEE wiring regulations (14th edition) in 1989.

However if you Google "voltage spike" this is the first result back : https://study.com/academy/lesson/vol...rotection.html

Back to the OP topic of jump starting a P3 V70...

My point is that the simplest method is to connect the battery terminals directly with the jump leads - -ve to -ve and +ve to +ve. I get that in your circumstances you will have been guided to connect the last -ve connection to bare metal - this is to avoid the risk of a spark near the battery which could potentially ignite hydrogen gas been emitted by the battery. However on all P3 Volvo models and I think P2's the batteries are closed vented - they're sealed and a tube is connected to the side which bleeds any gas under the car. On a later model P3 car it's actually not easy for an mechanically inexperienced owner to find a suitable bare metal are under the bonnet to attach the jump lead to.

Connecting the -ve jump lead to the chassis can cause problems if the reason why the car is struggling to start is a poor earth connection - e.g. earthing strap from engine to chassis. In this case the starter will get full power but electrical systems earthed through the wiring might see a rising earth potential - whilst this in itself is most unlikely to cause any damage it may result in a number of DTC's being logged and warning lamps on the dash that may need to be reset.