Jump Starting

[Munchie]

In the hope this avoids damage to vehicles.

Do not ever connect the earth from battery to battery as this can cause damage to the Engine Management system!!

Always consult the vehicle manual. :thumb:

The AA recommended method is:
Before connecting any leads make sure the vehicles are the same voltage and that they're parked with their handbrakes on and ignition off. The vehicles must not touch as this can cause sparks or an explosion.


Use the red jump lead to connect the positive terminal of the donor vehicle's good battery to the positive terminal of the flat battery.
Then use the black lead to connect the negative terminal of the good battery to a suitable earthing point on the engine or chassis of the other vehicle. This earthing point must be away from the battery and fuel system.
With both leads connected wait three minutes for the voltages to equalise before starting either engine.
Start the engine of the donor car and allow it to run for a minute then, with it still running, start the engine of the other car and leave both running at a fast idle for ten minutes. Do not remove the jump leads while the engines are running as this can cause serious damage to the electronics on either car.

If the jump leads get hot, then avoid a possible fire by switching off both engines and allowing the leads to cool.
Turn off the ignition on both cars and then disconnect the leads carefully in the reverse order to the way that they were connected. Be careful not to touch the clips against each other or against the car bodywork.

 

[GeorgeTelford]

Do not ever connect the earth from battery to battery as this can cause damage to the Engine Management system!!

Even if you connect from chassis to chassis for the negative it still connects one battery negative to battery negative.

Do not trust anyone who calls negative on a vehicle "earth", its the first clue that they have not got a clue what they are talking about.

The vehicles must not touch as this can cause sparks or an explosion.

Have they been watching to many American TV shows/films, in the real world cars do not explode on contact.

 

[GeorgeTelford]

PS this is not a dig at you Ken:Cool:

 

[RockieRV]

PS this is not a dig at you Ken:Cool:

Hi George

I am glad you have said that, because your first post does read as if you are

 

[Jim]

Sharon, that's is George's writing style but we are slowly bring him around to using smileys, as much as he hates them

^{_{Subscribers  do not see these advertisements}}

 

[steve&barb]

damn and there was me jump starting of me leisure battery

 

[Munchie]

What I posted was the recommendations of the AA.

I had an XJ6 jag which was in the garage for service and an apprentice used it to jump another car off. The end result being it "fried" my engine management card. The garage replaced this at great cost. This prompted me to read the "manual" and Jaguar had a paragraph warning against used the "negative" terminal on the battery, but to attach the lead to the engine "body" I think they would know.

 

[GeorgeTelford]

BTW that AA guide does not allow for positive earthed vehicles, the look of surprise when people find out the hard way is priceless.

So be sure that both vehicles are negative earth first (in this case earth is the conventional term, unfortunately)

Just researched the reason for not using the negative terminal. Its to idiot proof the connection procedure, ie if you were to do it properly connecting via negative terminal would not be a problem with igition off....

 

[Munchie]

Out of interest could some of you look in your car manuals re jump starting and see what they say?

 

[RockieRV]

Out of interest could some of you look in your car manuals re jump starting and see what they say?

What's a car manual?

^{_{Subscribers  do not see these advertisements}}

 

[Munchie]

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.

 

[GeorgeTelford]

What's a car manual?

Hi Sharon

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

 

[RockieRV]

Posted tid 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.

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

 

[Munchie]

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.

 

[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.

^{_{Subscribers  do not see these advertisements}}

 

[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]

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

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.:Blush:
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.

 

[TestPoster]

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

^{_{Subscribers  do not see these advertisements}}

 

[Jim]

Seems like we have all learned something from this thread, thanks guys, and thanks Ken for raising the subject, most enlightening. I've never been that carefull in the past, always relying on my nickname of lucky Jim, but I know now, thanks again. Forums are great, arent they?

 

[GeorgeTelford]

Lucky Jim or you Jammy git


Nice post Jon.


Just as a general warning, a battery when exploding does so with the force of a stick of Dynomite, but as I have always said the stick of dynomite doesnt hit you with lead shrapnel and sulphuric acid.........

If in doubt about the polarity of the battery terminals or the car's grounding polarity (or how to determine it at a glance) do NOT jump start

 

[Brambles]

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

I can answer this one . When you start the slave vehicle (dead one) you put a heavy load on the doner and the alternator will attempt to pump out full power. When the slave engine starts and this load suddenly disappears the alterator has to shed that extra power somewhere until the magnetic field in the rotor and stator collapses. It is called a load dump. As less current is being drawn it appears as a voltage. basically having all the lights and loads switched on means the alternator will be operating near maximum output anyway and so load dump is smaller and the loads switched on will all share the extra power keeping it within save limits, despite other protection being fitted in alternator on modern ones that 'should' give total protection. In reality if you just have your engine on a fast tickover it is not a problem. If you were to rev the engine hard and then start the other vehicle, you would get a very large load dump or voltage spike which in theory and in tests will not blow up equipment, but in practice can and does. Testing in a lab is one thing, but reality can sometimes be somewhat different, because of design tolerances, quality and possibly faults.
Again with large trucks, it is best not to have the engine running on the doner vehicle during starting of the second.

There will always be mixed opinion on this, and to be honest with modern vehicles it really is a last resort to use a second vehicle, and for one, I will NOT be using my Ducato again to start another car. NEVER. If I have to I will disconnect the battery and then connect up to second car, but why should my engine management then have to go through relearning because it got a full reset. Mind you it is not a bad idea to do it sometimes. An example is if the system has reset while you had a dirty air filter, it will have calibrated the air flows to suit, when you put in a new filter it ideally needs to recalibrate. BUT that is another topic so best left alone for just now. God! is this what 22 years in automotive electronic design has turned me into .. a rambling nattering confused geek. (but i do try not to use less techincal terms where I can). But please don't take my words as gospil, I often get it wrong.
Night night, Jon.

 

[Brambles]

Hi George

"... a battery when exploding does so with the force of a stick of Dynomite, but as I have always said the stick of dynomite doesnt hit you with lead shrapnel and sulphuric acid........."

I like that, can I pinch your saying and use it as well - very good!

 

[Ralph]

Having used jump leads to start cars for years I must have just been lucky as all this has made me pretty nervous of doing it again.
When I had a flat battery and called out the AA, the man had one of those portable units with jump leads attached. So as I have 2 leisure batteries I assume it would be best to just attach my jump leads to the spare leisure battery if I need to do it again?

^{_{Subscribers  do not see these advertisements}}

 

[scotjimland]

Hi Ralph,
not the best treatment for the leisure battery, they don't like high currents for short periods but better than being stuck, in saying that RVs generally have an emergency start switch which does just that..

 

[Ralph]

A quick Google comes up with this that seems to agree with Ken's posting. http://www.boschautoparts.co.uk/taJump1.asp?c=5&d=4 I guess Bosch should know...
However I still don't understand, as George says, what difference there is in connecting direct to the -ve of the battery or to the chassis or engine as they should all be connected together anyway.

And forgive my ignorance but are there cars with +ve earth these days? I know we used to have them years ago but I thought all modern ones were -ve. Has that changed again? I can't keep up

 

[Brambles]

Ralph, I tried to explain this in one of my earlier posts. When you connect the final connection of the negative clip to the battery you can get a spark. If there are any explosive gases about you may blow the battery up, or maybe just the gas. To avoid this hazard you connect to a main part of the chassis or engine preferably, away from the battery.
Jon.

 

[Ralph]

Duhhh
If you bash my head against something for long enough I'll get it (or I might just pass out)
OK, I see it now, thanks...

 

[Gonewiththewind]

Seem to remember reading that you could use a 9v battery (Duracell). cant remember exactly how. There is a gissmo now that swears to jump start a car using 4x1.5 batteries.
Strange old world.

^{_{Subscribers  do not see these advertisements}}