What tools should be carried in a modern car?

Not in 1978 they didn't! Twit of a boss I worked for started his Jag using a company Marina van as a doner - with a brick on the accelerator so it reved it's nuts off. Then blamed me when the van broke down a few days later with a shagged alternator. I was not happy when I found out! Consequently it's now doner car engine off when jump starting but *only* offer a jump start if I know why the other car battery is flat. I used a charged bike battery for the last jump start I did. Dave

I'm concerned with starting my own car - not a strange one.

If you know nothing about jump starting it would be madness to accept one from a stranger.

Yes they did. It's inherent in the design.

Wonder why he thought revving the engine to that extent made any difference to the alternator output?

And you are certain that episode caused the alternator failure just how?

Good way to end up with two flat batteries...

And that battery was designed to supply the current needed?

Err Norris Marina? Wasn't the ACR15 a consumable item?

Two flat batteries? Rubbish! It's soon obvious whether the recipient car is going to start or not, long before you have two flat batteries.

How did I know the alternator was duff? Easy - it didn't charge the battery. Van stopped with no lights/engine 10pm at night. Eventually diagnosed as rectifier pack failure. This happened 3 days after the engine reving episode on the first long run. Just a bit of a coincidence.

His car was a V12 Jag. The battery went flat 'cos the left the lights on (so I was told later). He put a brick on the Marina accelerator and wound the jag over on is starter motor until it ran. Didn't tell me though - found out some years later after I had left his employ.

Easily! no problem at all. Battery was from a Deauville, Yuasa, 9Ah,

Definately not an urban myth. I've seen too many ecus fried by people jump starting stuff.

Mainly because they connected the leads and almost instantly tried to start the car. People have no patience.

Why should this be so?. After all assuming a 12 volt system off another car why should that fry ECU's?..

Why should that matter?..

What failed in them? How did you test them? (Basically, no garage I know of has the ability to test an ECU - it's a specialist job)

Explain how that fries the ECU in one car but not the other? The power source is the vehicle with the good battery. How does that produce sufficient voltage to fry the ECU on the vehicle with a flat battery?

One possible way is for the alternator in the started car to be charging the combined batteries at its maximum output when the jump leads are disconnected, with the battery on the car which has been started still being almost completely flat, so having a higher internal resistance than normal, it can't fully damp the spike caused by the sudden change in current flows. The car with the fully charged battery suffers either no spike or a minimal one, as its alternator is not trying to charge the batteries.

Whether theory agrees or not, I've seen too many ECUs and other components fried on recently started vehicles to give or accept a jump start on a modern vehicle to/ from an unknown source. I do, however, carry a charged jump battery, which I connect, start the vehicle, and leave connected for a few minutes, stop the engine, disconnect it, then restart the engine. Never had a problem yet.....

I can't explain technically what happens; what I can say is that the damage is always done at the moment of disconnection of the jump leads. The implication is that the power source that causes the problem is the alternator in the "dead" car; there would be no electrical connection to the donor car, so no reason for anything to fry.

FWIW, I can understand your reasoning regarding the flat battery adsorbing any surges. I can assure you, and others here with trade experience have confirmed this, that it can and does happen.

In a similar way, I spend a lot of time tinkering inside computers belonging to myself and others. I know that 99% of the time I would get away with not taking anti-static precautions. However, I have a wrist strap, it's no problem to work whilst using it, so whenever I'm inside a computer I use it.

Chris

Yeah, I recommend one of those re-chargeable multi-led light panels. Can also be waved for warning traffic if stranded in an odd place

Jumper cable Fire extinguisher bottle Spare bulbs, yes. I believe this is mandatory to carry in France

Ideally, I would like to have a spare ignition cassette in the car, as this can fail without prior warning, but quite an expensive spare to carry

Well after a break of a few days I got around to having a play on our two cars. Engine running battery well up and then disconnected storage scope connected across battery leads and then battery disconnected a small pretty instant rise of around 150 millivolts!.. Tried the same on other car both Audis and almost identical. Course the results might well be different with a flat battery. I suppose I'll have to try that some time flatten battery in car A jump from car B and see the results when disconnecting the donor car..

Then perhaps that deserves some investigation. Car mechs are not in my experience electronic ones;!..

Well I'll not bother having had a few inadvertent belts on high voltage stuff;!.. Can't say I've every known a semiconductor device to be knocked out by static discharge ...

Indeed, but major manufacturers like Ford advise taking precautions. The AA went to the expense of adding extra equipment to the patrol's van, and training all patrols on its use. That's good enough to convince me it

Apart from inside the PSU, how would you "get a belt" from a PC?

Incidentally, are you aware that any proper wrist strap is of a high enough impedance for the expected voltages present to not represent an increased shock hazard?

How would you know? A device fails; how can you detect what caused it?

I worked with semiconductor devices in an industrial environment for many years; there were certainly failures that would have had static discharge as the most likely cause of failure.

Chris

My guess is plenty have run their battery flat because the ECU has failed (or whatever) then blame the AA etc for that failure after they've attempted a jump start. So making the use of some form of protecting mandatory is the suit's answer...

Ford likewise.

If your ECUs failed you don't get a flat battery, you get a non-running engine.

How does that account for the situation where the battery is flat, the engine starts when jumped, (so the ECU is fine at at that point) then it dies at the instant the jump leads are removed?

My (AA) stepson had that situation described to him when attending breakdowns on many occasions; each time, the ECU had failed. As I've mentioned before, there is no doubt that it happened to a T4 belonging to a family member.

Chris

So what actually did they do to that equipment then?.. Was this simply a mobile jump start unit which seeing the current needed must have been a battery based device?..

Was there some sort of over voltage breaker limiter involved and if so where does this overvolts come from?...

Well yes there may well be a problem, but what is the actual problem and how is it being caused?..

Umm .. I expect you'd see that I was referring to high volts stuff thats not likely to be found in a PC..

You'd be very hard pressed to inadvertently get a shock in a PC...

As maybe but I'd not like to get that caught anywhere;!..

I reckon that every semi device I have changed has failed in service in situ..

Even in circuit?..

In article , Dave Plowman (News) scribeth thus

Prolly right on the nails head with that one Dave;!...

There's a set of Zeners on the leads, you disconnect the battery from the leads 1st.

The alternator overvolting when there's no battery connected & a large load being disconnected, generally the other battery.