Jump Starting - Page 3

Jim · 12-09-2007, 10:49 PM

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 · 12-09-2007, 11:36 PM

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 · 12-09-2007, 11:54 PM

Quote:

Originally Posted by Fordson

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 · 13-09-2007, 12:00 AM

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 · 13-09-2007, 08:20 AM

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?

ScotJimland · 13-09-2007, 09:29 AM

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 · 13-09-2007, 11:50 AM

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 · 13-09-2007, 10:41 PM

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 · 14-09-2007, 07:10 AM

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 · 14-09-2007, 08:29 AM

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.