On Wed, 04 Jan 2006 11:04:20 -0600, Don Foreman
wrote:

On Tue, 3 Jan 2006 23:14:07 -0600, "Don Young"
wrote:

Since the running idler and load motors are directly connected in parallel,
wouldn't plug reversing with identical motors and no mechanical load have an
equal chance of reversing either motor? When running free, it seems to me
that either motor could be considered to be the source or load for the third
phase leg. I tend to believe that the idler requires more mechanical inertia
than the load to maintain the best functioning.

Interesting! The relative impedances are also important here. The
larger motor with lower impedance (and probably higher inertia) will
govern. Look at the terminal voltage where the two third legs are
connected. If the motors were perfectly matched, their effects would
cancel and this terminal voltage would be zero. If they are not
matched, the voltage (phase) of that terminal will be determined by
the motor with the lower impedance, and the phase of this voltage
determines (or indicates) the direction in which both motors turn.

If an induction motor does not "generate", is induced counter EMF imaginary
and the use of common induction motors as generators impossible? There are
many ways to understand and describe how things work and I like to think of
the RPC as simply a running induction motor with the magnetized rotor
inducing EMF not only into the line energized windings (counter EMF) but
also into the unenergized and phase displaced windings.

Right, up to here.

Note that, when
disconnected and still turning, an induction motor still has voltage across
its windings and loading this voltage with "braking" resistors will
mechanically load the rotor.

Only if the rotor has some significant permanent magnetism -- not
usually the case.




A squirrel cage motor DOES generate a back EMF and will continue
to do so for several revolutions after all power has been removed
even if it has zero permanent magnetism.

In the case of a 2 pole motor, at the instant of disconection,
the induced circulating currents in the short circuited rotor
inductance provide a diametrical NS field which decays at at the
rotor L/R rate for several tenths of a second. The voltage
generated by this decaying field is is easily observed with an
oscilloscope - the initial voltage is close to full supply
voltage.

Jim