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
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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.