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Brambles · 12-09-2007, 10:24 PM

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.

12-09-2007, 10:24 PM	#18 (permalink)
Brambles Member Funster No : 253 Join Date: Sep 2007 Location: Tayside Interests: Motorhoming of course! MH Type: C Class Years Motorhoming: 5 Posts: 47 Thanks: 0 Thanked 0 Times in 0 Posts	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.