Jump start kils ECU

Have you ever known a battery to explode through gassing? Except when on charge in a confined area? Hydrogen is one of the lightest of gasses, so will not hang around. Generally, when a jump start is attempted, it's in the open air.

I have blown up two by being careless, and it is not an experience to repeat.

Not quite an analogous situation but looks dodgy enough to me to be worth taking precautions.

Yes my renault traffics battery exploded burning my hand

Care to give the exact circumstances? As I said I've know them blow up when in a small charging area of a garage which is likely full of hydrogen from the many batteries. These days I'd expect it to be properly ventilated.

Well someone's got to ask, if its not an experience to repeat, why did you do it twice?

;)

There were about twenty years in between and the circs. were not identical, but fairly similar, the second was caused by inattention, the first by careless handling.

The first was when I had fitted a secondhand engine to a MK1 escort, the owner was there and it did not want to start, as the battery was down I connected up the seriously big Crypton charger and turned it up a bit while I fiddled about, I accidentally knocked one of the crocodiles and blam, luckily it just blew out a couple of filler plugs. I said that it was just something that happened occasionally when charging batteries.

The second time was about twenty years later, inside my camper van, the batteries are under the floor and open to the air, both had been on charge after winter disuse. The camper was not spinning over quick enough to start, so I connected the jump pack, in the dark depths I failed to get the polarity right and serious blam occurred, I was showered in acid (as the case ruptured), as was the interior of the camper, happily none went in my eyes or caused any damage to me or the camper, I was very, very lucky.

Google alternator load dump, the regulator only controls the field winding, so if the alternators delivering current into the battery on the donor vehicle & it's battery is knackered when you disconnect the jump leads there's a large dc current flowing & no easy way of reducing it. Bosch and all the major semiconductor manufacturers have info, & there's an ISO standard for measuring & simulating it. If you've still got an ACR17 then it's probably not worth worrying about though.

I'd rather not, since so much is speculation.

What has current got to do with it? To have a large 'current' flow into the ECU, it would have to have a low impedance.

On most cars the ECU doesn't have anything to do with controling the alternator, it's got it's own regulator

Which is why it's fairly rare, unless you've got a fault with the battery then you'll be fine.

Pretty spot on Arfa. Indeed, voltage regulators used on car electronics have already (or should have) a higher spec than the ones you'll find on most other things - ie a higher allowed input voltage.

It's certainly possible for an alternator with no load on it but the field coils driven to produce far higher voltages than designed to. Hence the reason to check the battery isn't totally dead, and will take a charge. And adding some form of surge suppressor when jump starting won't prevent this high voltage when the donor battery is disconnected under this sort of fault condition.

They do indeed, just not always high enough.

Good idea but somewhat impractical in most jump starts

Err why not, you disconnect the donor battery from the surge supressor 1st.

No it wont but it will dissipate its effects.

Any circuit with inductive loads can cause a power spike, if the circuits are interfeared with, its just as possible the spike could be on the ground side of the circuit.

Its rare but it does happen

Then additional means of preventing over voltage damage should be employed. It's hardly rocket science. But the very fact that 'better' (and more expensive) regulators specifically for car use are available means it's not necessary.

Turn on the ignition on the car - any signs of life? If not, don't attempt a jump start.

Fine if you leave the suppressor permanently in circuit. But if the 'flat' battery is knackered, the volts will still surge upwards when you remove it.

varistors serve a purpose but they cant be inserted in every cuircit just not practical

The biggest inductive load on a car is the starter motor. Which certainly does produce vast spikes when the current is removed. It also takes rather more 'current' than the alternator produces - and according to these articles it's 'high current spikes' that cause the problem. And of course, all ignition systems operate on just this principle. The primary device that prevents these spikes from doing damage is the very low impedance battery - and the way things are wired from it. It is already a very efficent surge suppressor.

Have you not noticed that it's always only the ECU which is damaged by this scenario? Never any of the other multitude of electronics on a modern car? So just how is it not practical to protect it if needed?

The main part of the alternator regulator is still in the alternator. The difference is it communicates with the engine ECU.