Jumping a car

EdGasket

Strider590 wrote: »

Right...... So how is that different to not having another vehicle connected?

What usually happens with jump starting is you connect up the cars, rev up the good one, try starting the bad one and it doesn't work. Then there is a lot of re-clamping trying to get a better connection with oxidised clamps/contact points that can actually pass the amps required to start a car. While this goes on there is much sparking (been there, done that) making/breaking contact and hence voltage spikes which take out the electronics imho.

Wig

RMS2 wrote: »

The 'donor' will be fine, especially if you remember to start it before turning over the other car.

On that other Audi A8 forum link, it was the donor car that got fried.

What they didn't say on the A8 thread was whether the donor was running, and more importantly, IMHO, whether it was being revved up.

Murielson wrote: »

Anyone remember the initial question from the OP??

As original post was 4 days ago maybe you have even resolved the issue by now?

The advantage of forums is that people from all walks of life can chip in and contradict other peoples views and through discussion, sometimes you can learn something you didn't know before. Or people will have steadfastly opposite views and will have to agree to disagree and at least then the rest of the readers (who don't hold either view) can make a more informed decision. .... your post seemed to be implying that people should not be discussing the topic in detail.
***************************************************

My own view on this subject has always been that there is a small risk to the electrics (I thought only the electrics of the recipient car were at risk but now I have learned that it is the donor car and possibly both cars).

I always connect the recipient -tive to an earth point as far from the battery as possible. I do this because it says in the Haynes manuals, but they don't say why it is done. The reason seems be a risk of sparks/gases. I think this risk is so small that it is probably not a problem (and I always used to connect the leads battery to battery with no problems, until I read the Haynes one day.)
The battery is flat, so how can there be any charging gases around it when you connect and cause a spark at connection? After it is connected there are no further sparks.
And once you connect the batteries you are immediately starting the bad car and there is no time for any gases to build up, and even if it takes you a couple of minutes, there would be little gas build up.
However, it costs nothing to connect the bad -tive away from the bad battery and it actually is easier to do it like that so why not do it.

The risk to the electrics seems to be voltage spikes and high current draw. Revving the donor car engine up will help the donor car alternator to overcome some of these issues, so that seems to make sense. Surge proteced leads sound like a very good option against voltage spikes. I have never used speacial leads and never had a problem, I have also always started the bad car with the good car running at higher revs. But this advice tells us to turn the good car off before starting the bad car
http://help.eurocarparts.com/how-to/jump-starting-a-vehicle/

After reading that article, I now ask... if you are going to turn it off, why not disconnect the leads aswell? Or at least try disconnecting them and starting the bad car, if it doesn't work then re connect them and try again with them connected.

Does turning off the donor car (with the leads connected) somehow protect the donor car?

After reading everything it seems the best way and the slowest way is to connect them let the donor fast idle charge the bad car for about 10 - 20 30 mins (take your pick) then disconnect the cars and try the bad car on its own.

If doing it with both connected, then turn all electrical ancillaries off on both cars. But as that Audi A8 owner found out, you can't turn off the ECU and the dashboard...

[Deleted User]

Strider590 wrote: »

Jumping a knackered battery is a false economy, it's potentially dangerous and at this time of year it risks leaving you stranded for half a day at the side of the road.

It's no more dangerous than jumping a non-knackered (ie. simply flat) battery.

A few years ago, my battery was so knackered that the alternator couldn't even "see" the battery (instrument needles were dancing like crazy), but I got it jumped and drove it to a tyre bay, near where I work, where it was changed.

Mankysteve

colino wrote: »

lee that is exactly the reason why you connect directly to a fresh donor battery and via an alternate earth on the casualty vehicle. With a flat battery it is acting as a giant resistor consuming power unnecessarily as you try to start with a jump. Keep on plugging away though and believing that the hydrogen produced charging a car battery will be fooled by moving the jump lead a foot away.

.

Lee exactly right. Alt earth is directly connected to the battery negative. There no difference where you attached the negative lead be it on the battery negative the engine or another earthing point. The only reason not to connect it to the negative terminal would be the reduce the chance or touching two the leads together.

Strider590

Bedsit_Bob wrote: »

It's no more dangerous than jumping a non-knackered (ie. simply flat) battery.

A few years ago, my battery was so knackered that the alternator couldn't even "see" the battery (instrument needles were dancing like crazy), but I got it jumped and drove it to a tyre bay, near where I work, where it was changed.

You got there with the power generated by the alternator..... An alternator doesn't "see" anything, it simply shoves out as much current as the battery will take and a knackered battery will take A LOT, the potential for overloading the alternator is high and the price of failure very costly.

burnt_toast_2

On Peugeots you need to soft start them if changing battery or jumping, turn side lights on FIRST then connect new battery or jump start to avoid spiking the BSI which is common on the Peugeot and is £700 for a replacement.

Wig

burnt_toast wrote: »

On Peugeots you need to soft start them if changing battery or jumping, turn side lights on FIRST then connect new battery or jump start to avoid spiking the BSI which is common on the Peugeot and is £700 for a replacement.

Hmm, interesting,
http://www.petercoopercarrepairs.co.uk/peugeot_bsi_reboot_procedure.htm
But according to the steps to follow in the above link, that should be...
Make sure everything all ancillaries & internal lights are set to the switched off position.
Have drivers window open. (if unable to open have someone inside the car)
Connect the batteries FIRST
THEN wait 10 seconds
THEN switch on the sidelight/headlight
THEN turn on ignition.

What a nightmare this is all becoming. I wonder do Peugeot owners manuals give a warning about disconnecting and reconnecting the battery?

EdGasket

Changing the battery on a Mercedes has been known to spike one or more of the SAMs modules. Some people advocate ensuring the headlights are switched on when connecting up a new battery; maybe to try and sink any transients though as it causes more current drain, the voltage spikes would probably be worse than with nothing turned on so on balance I don't like that idea.

http://mbworld.org/forums/c-class-w203/115277-list-faults-occur-after-disconnecting-battery-4.html