Slightly OT: cutting someone out of an electric car

"The electric car was so badly damaged in the crash that firefighters could not isolate the electric power meaning crews had to work carefully around the electrics because of the potential risk of electric shocks which could have caused a fire."
<http://www.cambridge-news.co.uk/incoming/man-dies-after-serious- accident-12792673>
I hadn't thought of that failure mode.
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Roland Perry

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On 25/03/2017 09:00, Roland Perry wrote:

I'd have expected there to be some sort of automatic battery isolation device if the car was subject to high g impact forces.
It isn't all that different to working on a petrol car where the fuel tank has been ruptured where the first spark could well be fatal (although they try to make petrol tanks so this doesn't happen).
Any energy dense power source is a real menace when compromised.
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This was a hybrid, so had a petrol tank.

But the emergency services have lots of training an experience to deal with petrol cars, and I think you'll find they very rarely burst into flames as a result of the rescuer's efforts.

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Roland Perry

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On 25/03/17 09:39, Martin Brown wrote:

+1
Surely if airbags can be set off by a certain g force it should not be beyond the wit of electric car manufacturers to include a "g force fuse" in the battery circuit, so isolating the batteries in the event of a crash.
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Jeff

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On Sat, 25 Mar 2017 13:45:38 +0000, Jeff Layman wrote:

Cars usually have a g force fuel cutout anyway. Why not a switch too?
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After serious thinking Bob Eager wrote :

They are a switch, my g switch switches off the fuel pumps, via a relay and triggers the hazards.
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On 25/03/17 15:13, Harry Bloomfield wrote:

There is a lot of difference between breaking the circuit for a fuel pump and that for an electric car.. The fuel pump will use 12V at a few amps; an electric car might be using 100V at 500 amps. If you try to break that with an ordinary switch you will get an unquenchable arc between the switch contacts.
A "g force fuse" would have to be designed break the circuit and quench any arc.
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Jeff Layman wrote on 25/03/2017 :

A not insurmountable problem. High voltage breakers have an arc quenching barrier, which drops into place when the breaker opens. Even the fuse in a 13amp plug top has a sand filling to quench the ark.
DC is more inclined to arc, but there are methods which have been in use for donkeys years to deal with it and for much higher DC currents.
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Air break contactors may have U shaped steel sections fitted in the insulated shield. Something to do with induced magnetism stretching and thus quenching the arc.
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On Saturday, 25 March 2017 09:39:21 UTC, Martin Brown wrote:

That's exactly what they have. It's under the passenger seat in my car. The battery is contained in a sealed steel box.
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remarked:

If it's not passenger-operated, then its position in the car is irrelevant. However, if it really is there, that's one of the worst possible places for the emergency services if they need to give it a manual "nudge".
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Roland Perry

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On Sunday, 26 March 2017 09:49:33 UTC+1, Roland Perry wrote:

Well, thats where it is. Mounted directly on top of the battery box. It isolates the battery automatically if there's a collision.
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remarked:

I wonder if we are cross purposes; is your car electric/hybrid, or internal combustion only?
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Roland Perry

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On 27/03/2017 22:12, Roland Perry wrote:

Full electic IIRC.
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remarked:

Don't they have a battery a bit bigger than "what would fit under the passenger seat"?
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On Tuesday, 28 March 2017 09:58:33 UTC+1, Roland Perry wrote:

The battery is 16Kwh and is spread bout under the floor. The anti-collision switch is under the front passenger seat.
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remarked:

But could be in many far more convenient places!
Incidentally, is this one of those fittings that doesn't change sides in RHD/LHD versons of the same vehicle?
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Roland Perry

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On 28/03/2017 12:19, Roland Perry wrote:

Isn't the switch Harry describes the one which detects the high G force and cuts the power automatically in the event of a crash? So being next to the battery is good, but doesn't need to be in a "convenient" place.
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until you need to reset it ;-)
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from KT24 in Surrey, England

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remarked:

****************** ********************

See above.
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Roland Perry

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