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[Nickbat]

This may seem a very odd question (two questions, actually), but here goes, anyway.

Is it possible to instantly fry an ECU by putting a strong electrical charge through the earth of a car?

I assume it is, but would like confirmation.

Secondly, if it is possible, what sort of current would be required and would it be possible to ensure the safety of any vehicle occupants at the time the charge is put through the earth circuit?

Weird, I know, but there is a reason I ask... 

[Marks DTM Calib]

Well no as a car has no earth!

As for passing a large current through the chassis, again no as the its not passing through the ECU.

If we were talking lightning then its a different matter though as the spark associated would have massive RF energy which could induce current in the ecu electronics and therefore blow it.

This is also the risk with welding as again there is quite a bit of RF (although modern systems are much more rugged)

[Entwood]

AFAIK the answer to your first is "Yes" .. and the answer to the second is the car acts a bit like a "farady cage", all the electric current passes through semi-monocoque construction .. the "outside" of the car, so the occupants are resasonably safe inside.

Also, the tyres, being rubber, act as an insulator so slowing down any transmission of current to some degree.. obviously if the tyres are worn and the metal caseing s touching the road this does not apply, and if you have one of those dangling "earth straps" it will increase the current flow.

Cars have been struck by lightning, and the folks inside emerge unhurt, although the engine electronics are usually toast and the tyres can be somewhat soft and soggy  (melted).

That is my understanding anyway ....  probably wrong

[Marks DTM Calib]

AFAIK the answer to your first is "Yes" .. and the answer to the second is the car acts a bit like a "farady cage", all the electric current passes through semi-monocoque construction .. the "outside" of the car, so the occupants are resasonably safe inside.

Also, the tyres, being rubber, act as an insulator so slowing down any transmission of current to some degree.. obviously if the tyres are worn and the metal caseing s touching the road this does not apply, and if you have one of those dangling "earth straps" it will increase the current flow.

Cars have been struck by lightning, and the folks inside emerge unhurt, although the engine electronics are usually toast and the tyres can be somewhat soft and soggy  (melted).

That is my understanding anyway ....  probably wrong

Unlikely to make a lot of difference as the steel band is not in contact with the steel rim so no direct conduction path.

Reality is that to get any conduction from the car body to 'earth' will require some pretty serious volts to break down the air and 'jump the gap' 

[Nickbat]

Well no as a car has no earth!

As for passing a large current through the chassis, again no as the its not passing through the ECU.

If we were talking lightning then its a different matter though as the spark associated would have massive RF energy which could induce current in the ecu electronics and therefore blow it.

This is also the risk with welding as again there is quite a bit of RF (although modern systems are much more rugged)

Thanks. I meant the negative circuit rather than the earth and as the current does not go through the ECU, you've answered my question I guess.

It all came about when I was watching one of those Police Road Wars programmes. During pursuits, patrol vehicles can come to within a few feet of a stolen car, yet have no way of stopping it and although stingers have some success, they are not the answer in some cases. I was pondering on whether a police vehicle could in some way disable the ecu of the pursued, perhaps in a similar way that a taser is used on a human.

As I say, just a thought - over which you have poured a bucket of cold water, Mark! 

[Marks DTM Calib]

If they could chuck a few 100KV through it from a low resistance source they might be able.

How about mounting a bloody geat big capacitor on the front!

Reality is that the energy in the likes of lightning is mahoosive.......

[sticka_v8_init]

AFAIK the answer to your first is "Yes" .. and the answer to the second is the car acts a bit like a "farady cage", all the electric current passes through semi-monocoque construction .. the "outside" of the car, so the occupants are resasonably safe inside.

Also, the tyres, being rubber, act as an insulator so slowing down any transmission of current to some degree.. obviously if the tyres are worn and the metal caseing s touching the road this does not apply, and if you have one of those dangling "earth straps" it will increase the current flow.

Cars have been struck by lightning, and the folks inside emerge unhurt, although the engine electronics are usually toast and the tyres can be somewhat soft and soggy  (melted).

That is my understanding anyway ....  probably wrong

I'm afraid i agree with the above.

[Nickbat]

If they could chuck a few 100KV through it from a low resistance source they might be able.

How about mounting a bloody geat big capacitor on the front!

Reality is that the energy in the likes of lightning is mahoosive.......

Fair comment, but I've heard that jump starting a car can fubar an ECU, so I was figuring that some form of electrical discharge through the chassis could have the same effect. I'd been thinking about a gas-powered dart with lines attached fired from the patrol car if the pursued vehicle came in a range of 4 or 5 feet.

Idle thoughts on my part, but thanks for your knowledge. 

[Marks DTM Calib]

If they could chuck a few 100KV through it from a low resistance source they might be able.

How about mounting a bloody geat big capacitor on the front!

Reality is that the energy in the likes of lightning is mahoosive.......

Fair comment, but I've heard that jump starting a car can fubar an ECU, so I was figuring that some form of electrical discharge through the chassis could have the same effect. I'd been thinking about a gas-powered dart with lines attached fired from the patrol car if the pursued vehicle came in a range of 4 or 5 feet.

Idle thoughts on my part, but thanks for your knowledge. 

Many an urban myth out there 

[Marks DTM Calib]

AFAIK the answer to your first is "Yes" .. and the answer to the second is the car acts a bit like a "farady cage", all the electric current passes through semi-monocoque construction .. the "outside" of the car, so the occupants are resasonably safe inside.

Also, the tyres, being rubber, act as an insulator so slowing down any transmission of current to some degree.. obviously if the tyres are worn and the metal caseing s touching the road this does not apply, and if you have one of those dangling "earth straps" it will increase the current flow.

Cars have been struck by lightning, and the folks inside emerge unhurt, although the engine electronics are usually toast and the tyres can be somewhat soft and soggy  (melted).

That is my understanding anyway ....  probably wrong

I'm afraid i agree with the above.

Some yes and some no 

The faraday cage bit is very true 

[aaronjb]

If they could chuck a few 100KV through it from a low resistance source they might be able.

How about mounting a bloody geat big capacitor on the front!

Reality is that the energy in the likes of lightning is mahoosive.......

Fair comment, but I've heard that jump starting a car can fubar an ECU, so I was figuring that some form of electrical discharge through the chassis could have the same effect. I'd been thinking about a gas-powered dart with lines attached fired from the patrol car if the pursued vehicle came in a range of 4 or 5 feet.

Idle thoughts on my part, but thanks for your knowledge. 

Watched Fast & Furious: Tokyo Drift, recently? (I think it was that one.. or maybe it was F&F 4.. one of them, anyway, showed something just like that being used to disable a car's ECU)

[Ken T]

I was wondering about the police being able to stop a car remotely. A Faraday cage will have a field inside of 0, however that is a perfect faraday cage that conducts perfectly, eg 0R which I don't think exists, there is always resistance. Cars being struck by lightning and killing the electronics show that in the presence of a strong electric field, voltages will be induced in wiring as steel car bodies are not a very good faraday cage. Pretty good but not perfect.

Suppose car manufacturers had to fit a CAN bus receiver module to the front and rear of cars, say in the lights, that would respond to a strong field and tell the main ECU to shut down ?. More use than the fairy lights currently being fitted to new cars 

Ken

[Marks DTM Calib]

If they could chuck a few 100KV through it from a low resistance source they might be able.

How about mounting a bloody geat big capacitor on the front!

Reality is that the energy in the likes of lightning is mahoosive.......

Fair comment, but I've heard that jump starting a car can fubar an ECU, so I was figuring that some form of electrical discharge through the chassis could have the same effect. I'd been thinking about a gas-powered dart with lines attached fired from the patrol car if the pursued vehicle came in a range of 4 or 5 feet.

Idle thoughts on my part, but thanks for your knowledge. 

Watched Fast & Furious: Tokyo Drift, recently? (I think it was that one.. or maybe it was F&F 4.. one of them, anyway, showed something just like that being used to disable a car's ECU)

PMSL....its a film!

[aaronjb]

If they could chuck a few 100KV through it from a low resistance source they might be able.

How about mounting a bloody geat big capacitor on the front!

Reality is that the energy in the likes of lightning is mahoosive.......

Fair comment, but I've heard that jump starting a car can fubar an ECU, so I was figuring that some form of electrical discharge through the chassis could have the same effect. I'd been thinking about a gas-powered dart with lines attached fired from the patrol car if the pursued vehicle came in a range of 4 or 5 feet.

Idle thoughts on my part, but thanks for your knowledge. 

Watched Fast & Furious: Tokyo Drift, recently? (I think it was that one.. or maybe it was F&F 4.. one of them, anyway, showed something just like that being used to disable a car's ECU)

PMSL....its a film!

I know. I was suggesting that was where Nickbat might have picked up the flawed idea. Not that it was feasible.

[Nickbat]

If they could chuck a few 100KV through it from a low resistance source they might be able.

How about mounting a bloody geat big capacitor on the front!

Reality is that the energy in the likes of lightning is mahoosive.......

Fair comment, but I've heard that jump starting a car can fubar an ECU, so I was figuring that some form of electrical discharge through the chassis could have the same effect. I'd been thinking about a gas-powered dart with lines attached fired from the patrol car if the pursued vehicle came in a range of 4 or 5 feet.

Idle thoughts on my part, but thanks for your knowledge. 

Watched Fast & Furious: Tokyo Drift, recently? (I think it was that one.. or maybe it was F&F 4.. one of them, anyway, showed something just like that being used to disable a car's ECU)

PMSL....its a film!

I know. I was suggesting that was where Nickbat might have picked up the flawed idea. Not that it was feasible.

No, I didn't see the film. Yes, it's a flawed idea, but it gets my goat when I see some scrotes in a nicked motor just feet away from a patrol car and then being able to go on to wreck cars, other people and goodness knows what. Considering practically all cars now rely on ECU chips and we're all told how sensitive they are, it was a logical thought for a non-techie like me.