Using Jump Leads and risks

[Mattsonics]

I've just used my Bongo to help a mate jump start a citroen van.

I was then told by a work colleague that there was a risk of damaging alternator by using jump leads from certain vehicles - I've never heard this before, and jump started many vehicles using my old landrover and other cars with seemingly no problems.

Can a Bongo alternator be damaged by using jump leads?

Thoughts?

Matt

[Bob]

Short answer, possibly.

Older cars aren't a problem but it is possible to bu***r up the ECU amongst other things on a newer one.

A bit here, loads more if you Google it.

http://www.carbasics.co.uk/how_to_jump_start.htm

I'd also strongly recomend wearing safety glasses as the battery can explode, that's why you don't connect the negative directly to the battery, but to a good earth away from it.

[timjonz]

I used to have a Vauxhall Omega & after not driving it for a couple of months the battery went flat, I got the AA to jumpstart it, after that the speedo & rev counter only worked intermitantly.
It may not have been related, I continued to use it for a couple of years eventually some one crashed into it & wrote it off so I got a Bongo

[Diplomat]

Tempting as the idea might seem, never start the "receiving" vehicle with the engine running on the donor vehicle as the donor alternator could become overloaded.

My policy is to give the flat battery a good half a minute or so charge from the donor car (with the donor engine revs icreased well above tickover) then disconnect one of the jump leads before trying a start.

Only as a last resort will I use both batteries paralled and definitely not with the donor alternator trying to supply the starting current.

It may be that it won't harm the alternator but I wouldn't like to find out miles away from home that the diodes had gone and there was no charge.

Frank

[mikeonb4c]

Interesting isnt it as you'd think having a dead flat leisure battery (which can happen) could overload the alternator similarly. My split charge relay is low power so is protected by 27 amp fuse, but the Willinton one is 70amps I believe so the alternator could be worked quite hard without a fuse to protect it until over 70amps was being drawn. Hmmmmm.

PS - I suppose the explanation is that a churning starter motor draws well over 70amps?

[Bob]

PS - I suppose the explanation is that a churning starter motor draws well over 70amps?[/quote]


It does Mike, but the altenator isn't turning fast enough to work. Bit like me on a Monday morning.

[dandywarhol]

Starter motor draws over 500 Amp son a cold day - as Bob says, the relay isn't on til the battery volts are around 13.2 from the alternator

[mikeonb4c]

500amps!!!!! crikey, that's shut me up

[bobngo]

its not only the doner vehicle which can suffer, i had a flat battery due to leaving the side lights on for a week in my garage.

called out homestart, they set up some jump leads ,from their very heavy duty battery.

started my car ok, homestart left, 2 minutes later my alternator was kapute !!!

phoned homestart told them the story , they said it was not unknown for that to happen as the load on the alternator charging a flat battery was so high,it sometimes blows diodes in the alternator

[Alacrity]

The way we do it here is to connect the jump leads up, start the 'donor' car, & leave them for a few minutes before attempting to start the dead vehicle (our jump pack says to do this as well). When the donor vehicle starts DO NOT disconnect the jump leads until you have added electrical load to the vehicle being jumped i.e. turn on headlight main beam, fan on full, heated rear window etc. etc. This has the effect of absorbing the ECU damaging voltage spike that you will get when you disconnect the jump leads & the 'dead' vehicles alternator suddenly see's a flat battery & ramps it's output up to max. Once it is all disconnected & settled down then you can shut off the electrical loads one by one & there will not be a voltage spike.

We have never had a problem doing this at all but the general belt & braces advice when jumping modern ECU laden cars is DON'T DO IT. Disconnect & charge the battery, then you cannot fry an ECU. Easy to say often not practical to do I know. I think the crude ECU's on the Bongo are pretty robust (as most are) but following the above steps should protect them.

Geoff

[Mattsonics]

Thanks to all - some helpful advice!

Matt

[Nevets]

Never mind about frying the alternator

£2000 for a body control module on some Mercs if you dont follow instructions....

as Alacrity says switch on some consumers for a few mins to be sure...