Apples/oranges Jim
I am talking about gasoline engines, You are talking about EV/hybrid.
I grant the point about relays can fail. However the failure if
generally no go, not full speed ahead.
The old military manual battery disconnect is still a good solution.
I was taking it further by mounting a stop switch on the steering
wheel, so the sheeple's hontoada/ki/hyunnis will be shut off by the
driver body hitting the switch in a frontal collision. this will
greatly lessen the chances of fire. The toada fuel pump continuing
to feed a fire after impact is apparently what caused one of my
daughter's friends to be burned so badly it took a month to identify
the remains after her new toada hit a rock wall.
My thinking is a master battery disconnect on gassers that is shut
off on impact would reduce fires. And, a manual switch could easily
prevent runaway gassers.
To my thinking, a big red Emergency stop switch tied to a Big hairy
relay (BHR(tm)) to interrupt the battery cable is the way to go.
This is not exactly a new concept. WWII vintage vehicles had a
battery master switch on the dash.
Relays are trouble points too, don't forget. I think the traditional
keyswitch _is_ all that is necessary if the hybrid's electric motor is
brushless. All you have to kill is the power to the gate sequencer
and that motor is _not_ going to turn.
(There would need to be some attention to failure-proofing the
design, so that, say, a shorted collector-to-gate motor IGBT didn't
back-feed power into the gate driver, which might make it to the
driver board's Vcc via protection diodes or the like. Board could
thus stay powered through the defective motor driver, and your
fail-safe key switch isn't so fail-safe anymore.
-- Jim
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