ViribusUnits

Well, the L-jet brain doesn't seem to be as sensitive. Nor any other car on the road today.

I've jumped the 928 several times. (Like going on 20 now.) Always from the frame, and positive terminal in the engine bay because it's easyer to deal with than getting to the battery.

When nothing is on, my Porsche's electrical system hovers between 15V and 16V, which is pretty normal as far as I can tell. I'm not worryed about that. As best as I can tell, it's in normal opperating specs, so that that.

I however, always use some very heavy guage jumper cables. I figure whats the point if your not going to use full sized equipment. It works well. They reside in the spare tire.

I've never had to raise the idle of the jumping vehical. Even when I had a defunct battery.

Paul D

Dr Bob makes a good point (as usual) about turning the motor of the donor car off before attempting to start the 'dead battery' car. The alternator's job when the engine is running is to maintain a specific output voltage level. The alternator does nothing when the engine is off or is being cranked over by the starter. When the ignition key is twisted the starter solenoid engages the starter motor. This requires LOTS of current to get the engine to turn over. When the solenoid engages the starter motor it's almost like putting a short across the battery terminals for an instant (voltage level will drop abruptly because of the very large current load). If the donor car engine is running at the time the dead battery car is turning over, the donor car alternator will be trying like hell to maintain that specific output voltage (which it can't). This will stress the diodes in the voltage regulator circuit. The diodes can blow immediately or maybe never (how lucky do you feel?). You won't notice that anything is wrong immediately, you'll have to wait till your battery runs out of juice because your alternator is no longer charging your battery after the diodes blow. Some people will even rev the donor cars engine while trying to start the dead battery car (I've done this too by the way) thinking it will help. This is even worse for the voltage regulator of the donor car since the donor car alternator will be able to supply more current while it is spinning faster when it see's the big voltage drop. Bottom line... it's better to turn off the donor car engine before attempting to start the dead battery car. Your alternator will thank you.

Lizard928

if you noticed I said to attach the negitiv then the positive to the dead car, no way to create a spark, and the only way your battery is going to blow up or do anything with sparks is if it is in really bad shape and I hope noone has a shark with a battery that bad!

JohanvdWalt

I see that the conversation is coming closer to what I initially posted, I did not suck it from my thumb nor am I a specialist in this field but I got it from the owners manual of my 2003 BMW 320d (witch I gave back to BMW for a full refund after the third blown turbo but thats another story).

It is the most comprehensive and logical way to do it I have seen and I'm sure it was written by someone who new what he is talking about so I stick to it.
I have to mention that they did not give the explanation just the method, the explanation was given by the service manager at the local dealership.

I used it on my Shark 4 - 5 times with no problem. I have tried starting cars previously without the engine running on the donor car but found that sometimes there's just not enough current.

While on batteries I believe that a car batteries was made to work, it does not like being fully charged all the time so on all daily used cars I have been leaving my park lights on for a couple of hours once every 2 to 3 months and my batteries tend to last much longer than before.

Johan