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

["David Roden (Akron OH USA)" <roden ald net>]

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."

> 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."


David Roden - Akron, Ohio, USA
1991 Solectria Force 144vac
1991 Ford Escort Green/EV 128vdc
1970 GE Elec-trak E15 36vdc
1974 Avco New Idea 36vdc
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