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Re: (ET) E12S and a curtis controller??
Andy,
I would be guessing if I told you a top speed of the tractor. The "Top"
speed in my E15 doesn't work (and I choose not to fix it since the new
controller will be in it in about two weeks).
The Alltrax controller automatically adjust the field strength to keep it
within a percentage of the of the armature current. The armature current
and the field current is monitored by the microprocessor and it decides,
based on programmable variables, what the percentage should be.
We believe the tractors will probably see an increase in top ground speed
because of the efficiency of the controller over the GE control system.
But
don't hold me to that because we won't know until we get the controller
tuned to the tractor motor. Another option, one I'm going to try, is use a
48v battery pack since the our controllers work on voltages from 24 to 72
volts, depending on model. I think another benefit of using a solid state
controller is the increase in use time. We can't know what that is without
doing a side-by-side comparison using identical battery packs. The field
weakening method used on the Elec-Trac's is to insert resistance in series
with the field winding which turns a lot of energy into heat.
A modern controller uses PWM to create varying voltages for the field,
creating very little heat.
Hope this is the answers you wanted Andy..
Thank you for your comments.
Steve
scr echoweb net
----- Original Message -----
From: "Andrew Poush" <agp vt edu>
To: <elec-trak cosmos phy tufts edu>
Sent: Friday, June 27, 2003 8:00 AM
Subject: Re: (ET) E12S and a curtis controller??
> I am not at all interested in a series controller for the E15 (compound
> wound motor). I want field weakening and the increased top speed that
> was available with the stock GE controls.
>
> Steve, will the proposed controller have field weakening? If so, can
> you estimate the top speed of the tractor (or the motor)?
>
> Thanks,
> Andy
>
> On Thursday, June 26, 2003, at 09:10 PM, Steve Richardson wrote:
>
> > 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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