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
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