On Sun, 27 Apr 2014 10:35:49 +0100, "Dave Plowman (News)"
wrote:

In article ,
Johny B Good wrote:
Oh yes it is.

you put a short across a leccy motor and it stops dead in its tracks mate.

I can certainly attest to that phenomenon from my own experience with
designing and building a controller board for a Philips solenoid
controlled bi-directional data cassette drive which used seperate cush
drive high quality permanent magnet DC motors (using proper carbon
brushes) on the tape drive hubs. This phenomena becomes ever more
extreme as you inrease the motor size.

On a car it is usual to short the wiper motor when it parks to make sure
they don't overshoot.

However, braking a car savagely from high speed is a very different
matter. The energy produced has to be dissipated somehow. Shorting the
motor and locking the wheels as suggested by NP doesn't seem ideal to me.

It isn't. It was just a point being made on the effectiveness of
regenerative braking. A real system doesn't simply short the motor
out, it uses the motor in 'generator mode' to absorb the energy into a
battery or supercap rather than have it simply dissipated as waste
heat in a brake disk.
--
Regards, J B Good