Re: (ET) uh-oh what'd I do now...

[Allan <allanhv worldnet att net>]

I agree that it sounds likely that it's a field problem.  The chattering 
may
be caused by the excessive load seen on the system when the field is not
present.

Some motors have stabilizing field windings in series with the armature in
addition to the regular field windings.  This is the case on our old E-20,
but I'm not sure what other ET motors.  When the "regular" field is not
energized, the only field magnetism comes from the stabilizing field
windings, which are reverse polarity from the "regular" field.  The
intention of these field windings is to keep the motor speed more constant
when the motor is under load and the armature current increases.  An
increase in motor load causes an increase in the armature current, which
causes an increase the stabilizing field current (in series) and thus
reduces the total field magnetism (counteracts the "regular" field), which
helps increase (stabilize) the motor speed, counteracting the increase in
the load on the motor.

I bring all this up just to make the point that motors with this feature
will run in the opposite direction if the regular field is not energized.
Without the regular field, though, the motor has almost no torque and draws
lots of current.  I'm sure running the motor under these conditions would 
be
very destructive to everything involved, since the current draw is much,
much higher than normal.



"David Roden (Akron OH USA)" wrote:

> Changing direction before the motor comes to a stop can weld or burn the
> contacts on the reversing relay (which on my tractor reverses the
> polarity on the field, not the armature).  That would fit with your
> statement that the tractor now wants to go backwards -- the motor's only
> field now comes from a bit of residual magnetism, and that's the last
> direction it ran.
>
> Don't try to run it this way, or you'll damage the commutator and/or
> armature.  Visual inspection may reveal the problem.  The relay is
> located on the back of the vertical panel in the rear of the front
> battery compartment (at least it is on my E-15).
>
> To confirm or test, disconnect one of the armature terminals.  Then with
> the rear wheels off the ground and trans in neutral (for safety), apply
> motor power and measure voltage across the field at the motor.  If it's
> zero, that's probably the problem.  New reversing relays are available
> from Bill Gunn.
>
> David Roden - Akron, Ohio, USA
> 1991 Solectria Force 144vac
> 1991 Ford Escort Green/EV 128vdc
> 1979 General Engines ElectroPed 24vdc
> 1974 Honda Civic EV 96vdc
> 1970 GE Elec-trak E15 36vdc
> = = = = = = = = = = = = = = = = = = = = = = = = = = =
> NOTE: If you receive an email which exhorts you to "Send
> this to everyone you know," you don't know me.
> = = = = = = = = = = = = = = = = = = = = = = = = = = =