ksebruce

Posted the tip with good intentions based on info from engineer who serviced my jag and what I read in the manual and what AA had to say.

Methinks I'll keep my own councel from here on in.

__________________
Ken n Steph

You can't have a rainbow without rain!

GeorgeTelford

Hi Sharon

You know, its the book the male looks at when everything else as failed

RockieRV

Hi Ken

Sorry, I'm in a jovial mood - didn't mean to rub you up the wrong way. It was a good tip, but as I am technically challenged I thought I would still partake

ksebruce

Hi Sharon, you didn't rub me up the wrong way.
I was posting and had to go do something when I finished the post yours had beat me to it.

__________________
Ken n Steph

You can't have a rainbow without rain!

pappajohn

hi,
during my short lived apprenticeship(cant take orders) i was always told to connect the neg lead to a suitable engine/body point on the dead car LAST as, if the battery had been gassing, there was a chance of explosion if the lead sparked on contact with the battery neg. if connected to a different point it should be far enough away from the battery not to really matter if it sparked.

im sure with the advent of the ECU/EMU connecting to all terminals could cause a power surge and 'spike' the ECU, but i have my own views on this and i've never experienced it, after all, the handbooks state ignition MUST BE OFF when connecting, presumably to isolate the ECU.

the other point about not touching vehicles goes back to the days of chrome bumpers ect. if the cars were touching you already had an 'earth' connection so when the pos lead was connected this could spark and do the same as in explaination one.
plus in the days of pos earth you would certainly know you got it wrong. if one car was pos earth and the other neg earth it would be the same as connecting two batteries POS-NEG and NEG-POS.(BANG)

john.

GeorgeTelford

Hi Ken

Keep your own council? The beauty of forums is that info can and will be checked by others, nobody should expect their posts to be right all the time or even info they are passing on, I dont expect that and apreciate any effort to improve the info thats posted.

The AA should know better than to assume all vehicles are Neg Chassis and explosions from Cars touching is ludicrous, that doesnt mean that you did wrong by posting it.

Pappa

The look's on the faces when they do get crossed is priceless, I have seen 2 instances of people crossing over

pappajohn

done it myself when i worked on breakdown recovery. 4am, snowing, middle of north yorks moors. courting couple with radio on (dont know why)for hours and flattened battery. got pos and neg reversed for about 50 millisecs. in my tired state i scared myself stupid. never done it again.
john.

Brambles

It is my opinion, and through experience you should not use a vehicle with an electronic management sytem to start another vehicle with it's engine running. You should actually stop the engine of the donner vehicle after allowing the 'dead' vehicle to charge for a few minutes. The reason is the voltage dip that occurs when starting. The management sytems are desined to be immune to this large dip while starting, but once running any large voltage dip can really upset it as it will be up an running in full operational mode and doing all sorts of operational checks and looking for faults and doing it's job. It can easily detect faults that do not exist and lock out certain functions. It may even lock up the processor completely and fail to work until given a full power up reset by disconnectimg the battery for a few minutes and reconnecting.

Regarding the negative connection lead it is normal to connect that second in case you drop the last clip you put on. Imagine connnecting the neg 1st, then the positive and when doing the second pos clip you drop it or even accidently rub it against a metal object. BANG!. If you drop the neg clip then it will be a lot safer as you will only have the charge current flowing.

If you connect the leads with the doner engine running and say the 'dead' car has a shorted battery, then you will be putting a massive load on your alternator and it could damage it.
So wise way is to cautiously connect the final lead. If the 'dead' battery is shorted, you will know about it. The reason recommendation is to connect to part of the chassis/engine is so you do not get a large spark next to the battery.

In summary. If the vehicle you are tryingto jump has been attempting to start but just flattened the battery in doing so or is a result of lights being left on etc, then fine. Battery should be ok and should not cause damage to doner vehicle.

If 'dead vehicle is an unknown, say for example been sitting for a week and you have no idea of the condition of the battery and appears very dead. DO NOT even attempt to jump start from your good vehicle .. just not worth the risk. Best way there is to use a spare battery to give a jump, but better still to initally put a battery charger on to make sure battery wil start to charge. After it is brought up to 12 volts approx, then you can jump start.

I think that all makes sense, over to George T to comment if it makes sense as easy to write what I think is right but can be read differently, especially at this time of night.
Jon.

kands

Very nice, clear and concise post Jon, thanks. I am sure that there is no room for confusion on this important subject now.

Keith

Supertractorman

Many LGV Transport Companies recommend to Drivers when jump starting, that the Donor vehicles engine is running and all lights, heaters and other electrical equipment is switched on on both vehicles in case of surge damaging ECU units etc