What tools should be carried in a modern car?

The resistance of the antistatic straps is enough to limit current from even a 240 volt contact to microamps.

Not saying that wouldn't be fatal, but DC normally has a frequency of zero Hertz, with maybe a bit of AC ripple superimposed. Unless you meant pulsed DC?

Seconded.

OOPS!

It was 4,500vac; apologies for the typo!

Chris

Sorry for assuming you'd understand 'run the battery flat' meant while trying to start the engine with a fault.

I'm not inclined to believe these sort of reports. Too many variables.

Variables?

I don't care whether you believe them or not. The "reports" came to me in casual conversations with my stepson at the end of his shifts, when we would often chat about what jobs he'd done that day. He had no agenda, and neither do I, other than trying to help others avoid problems.

Chris

Although in all the situations I've described, the engine *DID* start, only to stop when the first jump lead disconnection was made.

With respect, how many cars with an ECU have you jump-started in your lifetime?

My stepson was regularly working a 60-hour week, doing perhaps 15 or 20 calls a day. A high percentage of those were to flat batteries, so he would have been exposed to the potential for the failures I have mentioned on a frequent basis.

Dave, you choose to continue to believe it can't happen if you wish; I still urge all others to take the simple, sensible precautions I have outlined.

Chris

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Duncan Wood" saying something like:

Pretty much, yes.

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Dave Plowman (News)" saying something like:

Exactly so with my Tranny. There's a big red flip cover in the engine bay for the pos lead of a set of jumpers. However, I wouldn't be at all surprised if some cars/vans have a fragile/badly-protected ECU, so it would make some sense to guard against the possibility of damage.

So these diodes then, they are arranged so that they clip the assumed overvoltage on the donor battery or charging system in the donor source on or supplying that battery?.

But why?..

Can we assume that this donor system is a car or van system and if so why isn't that affected by such overvolts?. Surely the assumed good battery on the donor vehicle will be of sufficiently low resistance to prevent this happening?..

So OK then this is a battery thats charged from the patrols van. Its assumed we disconnect the charging source then thats taken to the dead vehicle. OK so where is this surge to come from then that battery is hardly likely to have additional volts thereon?..

OK so this to is from the patrols vehicle so where is this surge to come from and lets assume to that the patrols vehicle is involved in all this so why isn't its electrical system damaged then?. Because of the surge suppression?, so where does this damaging surge come from then?..

So a set of jump leads presumably to come from any vehicle to and dead vehicle?.

So where from the surge?..

So this dead vehicle has the clips from the good vehicle supplied to it so dead vehicles system volts suddenly rises. OK so that we might presume is around 11 to 12 volts unless the charging system is on the go from the donor vehicle so thats what around 14.4 odd volts so thats going to damage the dead vehicle?..

So are we of the belief that the dead vehicles electrical system is going to be knocked out bu the sudden imposition of a another battery source applied to the one already in place?. Or another "battery" in effect with 14 odd volts on it if this is the case then theres something very seriously wrong with the design of a modern electrical system somewhere that it cannot stand or cope with that!...

Perhaps theres some other mechanism thats into play here like a latent ECU fault or a units thats failed anyway..

Are we assuming that these callouts are to people who have dead batteries where they've left something switched on so the battery's flat i.e. discharged or the vehicle apparently won't start perhaps turns over but doesn't fire, or won't turn over and its assumed that the battery's flat, no or very low volts so when its now jumped then it starts then when the donor power source is removed then it dies and the ECU is fried???

So when perhaps we re connect the donor power its all over and won't start or run again?..

Maybe not but I'd like to know -why- this should be so;!...

Well up to 15 kV on UHF TV 'mitters;!! A belt was rather difficult to obtain.. I could tell U a good yarn of what happened to someone in a remote country who did manage to bypass the system in operation which was a differing environ to "test" !...

How do you know that and how could they unless the design was very poor such potentials managed to get where they could do such damage?..

Yes agreed, very odd .. there must be something else going on there somewhere this just does not make sense...

Did they ever explain what was causing the ECU's to fail in this mode at all?..

Then this must be very poor design that such a potential can arise across the chip that can damage it unless were now into severe over volts, spikes and such that aren't really static discharge?..

They?

Chris

Might I respectfully suggest that you are asking in the wrong place then?

Chris

The electrical system of a car is a pretty hostile place even before you attempt a start from an external source. A 'fragile' ECU wouldn't last 5 minutes without adequate protection.

No, they're on the side you attach to the flat battery

Which you then detach.

The alternator on the car with the dead battery

Because it's dis

? Because of the surge

How many times are you going to need the same answer.

No

Nobody's suggested that

Except that it does run till you disconnect the jump leads.

Because the alternator on the flat vehicle with a buggered battery generates the surge. Hence why you can get surge supression fitted in alternators or fit separate ones like Jaguar do.

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Dave Plowman (News)" saying something like:

Common sense doesn't dictate design in some makers' drawing offices.

Assumed the AA or other recovery outfit that went to all the bother of fitting these surge suppressors....