Jump Starting Someone Elses Car

[javadude]

If I use my lex to jump start someone elses car then can it fry my electrics?

[Fmrl]

I hope not - I jump started my neighbours Merc the other week!

[L3XUSIS200]

I WONT DO ANY DAMAGE UBLESS YOUR TRYING TO JUMP START A LORRY LOL

[Steve]

I would not even entertain jump starting someone elses car... i even threw my jump leads in the bin!

[Steve]

I WONT DO ANY DAMAGE UBLESS YOUR TRYING TO JUMP START A LORRY LOL

yeah the mercedes!

[ColinBarber]

If I use my lex to jump start someone elses car then can it fry my electrics?

Yes it can, although it's normally the car that is being started that will be damaged if not done correctly.

[MrADeveci]

As far as I know, like Colin said, it's the other car that can be fryed.

All that I would suggest is that the other persons put on ALL the elctric, hazard lights, radio, wipers, and anything else that can come on ...

So that when the car receives a big jump of voltage, it has somewhere to disperse it, and doesn't fry the car !

[Steve]

not according to what the AA told me colin when i jumped someones car.. he said it was a silly thing to do.

He had me worried

[Fmrl]

not according to what the AA told me colin when i jumped someones car.. he said it was a silly thing to do.

But isn't an AA chap bound to say that? :duh:

[ColinBarber]

If possible don't jump start or have your car jump started. If it cannot be avoided then once the jumped car is started you should leave it running for a few minutes so that the Battery gets some charge in it and therefore the alternator output is reduced. Then before the leads are disconnected the headlights, rear window heater, fan etc should be turned on on BOTH cars. When you disconnect the leads any spikes are absorbed by the devices you have turned on and not by your cars electronics.

[javadude]

Thanks everyone. Think I'll avoid doing it in future then....

[Maz]

You said before we should use booster to start the car, may i ask what kind of booster we need Colin? will i able to get them in Hardford or motorworld?

[iains]

A cheaper way is to get yourself a spare Battery from Costco (bosch or the like) and some leads.

I have to say that this whole thread confuses me a little. I've jump started loads of cars in my time, never had a problem and would be very surprised if I had to. All you are effectively doing are increasing the cell composition of the Battery and therefore theortical ampage of the Battery (ie: bigger Battery!) when you provide a boost / jump. The damage you are talking about would occur to either cars alternator due to:

1. The boosting car - Battery has increased load - possible alternator damage

2. Flat car - alternator piling current into flat Battery = working hard.

In the either case surely the same applies when the alternator is under hard load ie:cold winer morning - deminser, heated seats, lights and radio playing from cold start?? Therefore assuming you don't try am jump something out of your league (so as to speak) then you should be okay.

I think you would have to be very very unlucky to fry anything either car (assuming they were or relative cranking amp ratings). As for the voltage jump - I would think the Battery would absorb the majority of that as "charge" - you need more than 12v to charge and 12v Battery. Also, if the voltage spike was so bad, the fuses would go pop (unlikely).

I caveat this as I am not an electical engineer and so may be talking absolute rubbish....

[d3fy]

<Snip>

I caveat this as I am not an electical engineer and so may be talking absolute rubbish....

But is sounds like good rubbish :winky:

[ekky]

I would jump start another car, but you can buy jump leads that have surge protection built in, and I have seen a surge protector that you can clamp onto existing leads.

[ColinBarber]

The main problem is the car with the flat Battery cannot absorb any voltage spikes when it is completly flat. If you disconnect the other Battery too soon the alternator output will be too high for the sensitive electronic components. Clearly the design of these devices will affect its ability to withstand these spikes but it is quite common for damage to be done.

Bosch recommend that you turn on all electrical devices before you disconnect the lead to minimise the risk.

To show you this can happen have a look at this company selling ECUs which it states the main cause of failure is due to jump starting:

http://www.bba-reman.com/rovermsb.htm

[Claire G]

Hubby used to work for Honda many moons ago, and the mechanics told him it could damage the engine management chip if you jump started someone's car from your Battery.

Wouldn't take the risk personally!

[iains]

Fair enough - I stand corrected.

I'm still very surprised by this - knowing how sensitive computers are to voltage surge I can appreciate this, but I still query the fact that the ECU should have (or not as the case may be) sufficient isolation built in, but I guess it's a question of cost.

Also, as I recall, the owners manual makes no reference to this issue?

[Claire G]

I don't have a definitive answer one way or t'other, but don't fancy taking the risk.

My friend managed to do something to the electrics when she jump started another car - all the lights came on and everything had to be reset etc. Not sure if it was coincidence or not, but that was on a Citroen Saxo and I can imagine a Lex would have more complex electrics or at least be more to fix!!

[amolkarnik]

i had once helped someone jump start a car from mine (BMW). that guy was a mechanic and said that as long as i had my engine running, it was ok. nothing happened, but i doubt if i;d risk it again.

[Scorpion]

Just to throw a spanner in the works: I've jump started another car from the Lex with no problems whatsoever.