"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."
I hadn't thought of that failure mode.
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.
A friend of mine competes in sprints and hillclimbs in an electric car and he tells me that the marshalls have been instructed that in the case of a crash and subsequent fire (admittedly unlikely without a tank full of inflammable liquid), the car is to be allowed to burn out, because of the potential risk of electric shocks.
In message , at 09:39:19 on Sat, 25 Mar
2017, Martin Brown remarked: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.
I'd be more worried about the damage to the battery causing a runaway short circuit induced explosion or fire. I've often wondered how well batteries would stand up in a crash. I guess in the end only time will tell us. Brian
At least if it is on fire it is fairly obvious that it is a hazardous situation so you can let it burn out till anything flammable as been burnt and the remains are no longer that hazard. Damaged cables may make parts live but not as part of a circuit so the hazard will remain to handlers until things can be isolated or the batteries discharged in a controlled fashion. Just leaving a crashed vehicle untouched while the batteries self discharge is obviously not an option as a sensible method of dealing with one.
G.Harman
In message , at 12:54:09 on Sat, 25 Mar 2017, snipped-for-privacy@yahoo.co.uk remarked:
Even if the driver's still inside and still alive (just).
+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.
Cars usually have a g force fuel cutout anyway. Why not a switch too?
They are a switch, my g switch switches off the fuel pumps, via a relay and triggers the hazards.
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.
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.
In message , Harry Bloomfield writes
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.
That's exactly what they have. It's under the passenger seat in my car. The battery is contained in a sealed steel box.
In message , at
01:21:35 on Sun, 26 Mar 2017, harry 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".
After a significant bump my plug-in hybrid is supposed to shut off the fuel and "high voltage" electrics - I'd be surprised if they didn't all do that.
Well, thats where it is. Mounted directly on top of the battery box. It isolates the battery automatically if there's a collision.
Lithium batteries burn really well. That's why they're in a steel enclosure. ISTR several electric cars have caught fire on the production line.
In message , at
10:27:30 on Mon, 27 Mar 2017, harry remarked:I wonder if we are cross purposes; is your car electric/hybrid, or internal combustion only?
Full electic IIRC.
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