Re: (ET) E12S and a curtis controller??

["Steve Richardson" <scr echoweb net>]

David Roden Wrote on Jun 26 2003.


> On 25 Jun 2003 at 19:08, Steve Richardson wrote:
>
> > A series controller
> > cannot be used on a shunt wound motor ...
>
> Although it's not an ideal situation, a series type controller ^can^ be
used
> with a shunt or sepex motor, provided the concern below is addressed AND 
> a
> source of power is provided for the field.  I quote from a Curtis manual
> for an older model PMC-25 controller:
>
> "The PMC does not provide current for separately excited fields such as
> those found in shunt and compound motors, and may be considered as being
> designed for series wound motors.  However, the controller may be used
with
> shunt and compound motors if a separate source of field current is
provided.
>  For motors with shunt fields wound for full battery voltage, the shunt
> field may be connected across the entire battery pack via a contactor.  
> In
> such installations a freewheeling diode should be installed across the
field
> to prevent arcing across the contactor as it opens.  For motors with 
> field
> wound for less than full battery voltage, or in cases where field control
is
> desired, either a separate transistor field controller is required, or 
> the
> field may be connected to various taps off of the main battery pack."
>

All true David, but you can also use a Volkswagon to move large qauntities
of gravel if you "Re-Engineer" it enough.  I guess I should have said;
"You can't use a series controller to run a shunt motor unless you make
provisions to somhow activate the field winding".

We should also mention that it is imperitive that the field winding be
energized First on a shunt motor.  Without an energized field the the
armature will draw exessive amounts of current which will destroy it.

> > A series controller can be used on PM motor though because it looks
> > like a series motor to the controller.
>
> Yes, but be careful!  The series field adds a significant amount of
> inductance to the series motor.  Depending on controller design, that
> inductance may be essential to the proper operation of the controller's
> current limit circuit.  When such a controller is used with a PM, shunt,
or
> sepex motor, excessively low circuit inductance can cause abrupt, jerky
> starts and/or accidental overloading and destruction of the controller's
> power semiconductors.
>
> This has been a problem with Curtis controllers in the past in some
> applications; I don't know about ETs though.  I couldn't say whether the
> rather small series field in our motors has enough inductance.  I 
> wouldn't
> want to assume that it does.
>
> Very often a controller intended for a series motor will need a large
> supplemental inductor in series with the motor when it is used with a PM,
> shunt, sep-ex, or even a compound motor.  Quoting again from the Curtis
> manual: "When a series winding is not provided in the motor, such as in a
> pure shunt motor, an inductor must be added in series with the armature 
> in
> order to provide the inductance which would normally be supplied by the
> series winding."


I'm so glad you quoted the Curtis manual !  Our controllers do not need
extra windings because of their superior design.  Ours are smooth and they
don't whine !
Alltrax controllers are very happy with PM motors like the E-Tek motor made
by Briggs & Stratton.

Thanks David

Steve Richardson
scr echoweb net