Re: Production EVs

[Thomas Shay <tshay@ix.netcom.com>]

Bill Dube' wrote:

> Believe me, there is no chance that any parking brake will stop an EV from
> driving off if the controller fails "on" (whether it is AC or DC)!
>
>     The stall torque on a series-wound DC motor is enourmous. If you were
> able to stop the wheels from turning somehow, something would have to "give"
> in the driveline. Perhaps it would be the clutch. It might be the
> differential, but the motor *will* turn.

   This doesn't make sense to me and it doesn't square with my experience.Brakes
on my Ranger pickup are strong enough to stall the motor in 1st
or reverse gears.  If the parking brake is set hard, it can prevent forward
motion but it's not strong enough to prevent motion in reverse.

   If my brakes couldn't hold or stop my motor,  I'd be working on the
brakes or discarding the EV.  The brakes must be the first defense
against a runaway because stepping on the brakes is instinctive  The
brakes should at least start slowing the car and give the driver a little
time to decide what to do next and to do it.

  The notion that the stall torque of a series DC motor is irresistable
is simply nonsense.   At the typical current limit of 500 amps, the ADC
9-inch motor pulls like a 2-liter gas burner; at 1000 amps it pulls like
a medium size V8.

Tom Shay