Voltage spikes perhaps?
This can be prevented by doing the following:-
Connect the jump leads between the two vehicles. Earth connections on last, and off first. Do not connect the earth lead from the donor car to the car battery of the car receiving the jump. Connect it to somewhere like the engine block or other earthing point.
Start the engine of the vehicle providing the jump start.
After 5 minutes, start the other engine.
Start attempts should be made at intervals of 1 minute not last longer than 15 seconds.
After starting, allow both engines to idle for approx. 3 minutes with the leads connected.
In order to avoid excess voltage in the electrical system, before removing a lead, switch on an electrical consumer (e.g. light, heated rear window) in the vehicle receiving the jump start.
Disconnect the jump leads. Remembering, earth connections off first.
Edited by Dynamic Dave on 03/12/2009 at 19:10
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The driver's manual usually contains instructions.
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The driver's manual usually contains instructions.
>>>>>>> is that the paragraph before or after the
"refer to dealer"
bit
0 ---- {]
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Even if the alternator is capable of shoving out 18V, wouldn't the other battery have a smoothing effect?
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The driver's manual usually contains instructions.
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Agree. Do not guess. RTFM.
Certainly Ford instructions are "interesting" re what to turn on and what not to turn on prior to disconnecting leads.
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The DD and BB posts are very interesting. I would hope that the DD method would put a degree of charge into the flat battery thereby (hopefully!) preventing the damage that BBs link so clearly describes.
However, I don't understand why the earth lead to the faulty car should be connected to the body/engine rather than direct to the battery. Surely this might creates current where you don't want it?
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The idea behind this is that when the car has been started & the battery has charged this earth lead will be the first one to be disconnected.
As there will still be some current circulating through this lead, sparks will probably be created. It is therefore best that these sparks are as far away from the battery as possible to avoid igniting any hydrogen gas created by the battery charging.
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Whilst DD's post is closest to the mark, I would never start the car whilst the donor engine was running. I would run the donor for 10 minutes, turn off, disconnect the earth then start the other car. 'Why' I hear you say. If you start the car whilst still connected your alternator can see a huge demand for current that can damage your alternator and as a result can spike your ECU. Regards Peter
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>>However, I don't understand why the earth lead to the faulty car should be connected to the body/engine rather than direct to the battery. Surely this might creates current where you don't want it?
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I have always understood :-
1. As mentioned - hydrogen - but modern batteries are "sealed"
2. Clip the nuetral to the engine as that is where you do want the spark and it is a shorter path than via the battery and a little less voltage drop.
(There used to be a nice metal loop at the front of the rocker box to attach a hoist to.)
Not sure if 2. is relevant with modern electrics
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>>Re DD instruction, which seem to come from his user manual
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>>"In order to avoid excess voltage in the electrical system, before removing a lead, switch on an electrical consumer (e.g. light, heated rear window) in the vehicle receiving the jump start."
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My Mondeo II instructions include
Do NOT connect the negative to the terminal of the flat battery.
Connect it to the engine.
Disconnect
To reduce voltage peaks on disconnection, switch on the blower and the heated rear screenin the vehicle with the flat battery.
Do NOT switch on the headlights in place of the heated rear screen. The peak voltage could blow thw bulbs.
Obviously one would switch everything off , obviously engine, lights and hazzards but I guess it is easy to forget the A/C
So my repeated suggestion, no plea is please RTFM and ignore grandads way :-)
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Most important warning that DD left out !( just forgot to add) ENSURE the keys for the car with the flat battery are removed from the ignition & away from the vehicle whilst connecting.
This is because on some cars when the key for the vehicle is in the vehicle some of the electronics are active & if the battery is dead flat & a donar vehicle is coupled up the vehicle can be spiked before the ignition is turned on!!!!!!!!
Moral of the story is use a ni-cad battery pack or call an experienced operator. On my service calls this week with the frost I have come across 3 vehicles that have been connected up wrongly in just one week. Blown ECU's dashes,sat navs autos boxes & alternators ABS modules etc etc. loads of dosh
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