Re: (ET) Electronic controller

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

On 9 Jan 2002 at 0:47, David Roden (Akron OH USA) wrote:

> The only cautionary note I would sound in using a controller intended for
> a PM motor is you should probably have some kind ot switching system that
> ensures that the field is always energized ~before~ voltage is applied to
> the armature, and that the field is always shut down ~after~ voltage is
> removed from the armature.  (This might not be so important with a
> compound motor, but it's still a reasonable precaution.)

And just a little while later I ran across this comment about separately 
excited motors on the EV mailing list:

= + = + = + = + = + = + = + = + = + = + = + = + 

... you have to be very careful in controlling a sep-ex motor, especially 
at high voltage.  The motor is the inductor, but it looks like a SHORT 
CIRCUIT without the field energized properly first. 

Without interpoles you have to be extra careful with field weakening.
(even with interpoles you have to be careful).

If you keep the field energized to an appropriate level, this won't be a 
problem.  But the gray area is how far you can field weaken without 
creating a fireworks show on the commutator.

I guess this is why sep-ex has never been very popular in the EV hobbyist 
community.  You really have to [know] the motors capabilities or have a 
pretty good controller.  This is not real difficult, but there are very 
few control vendors that offer a good sep-ex control. 

The other problem is that the sep-ex control should be matched with the 
motor.  This is not always the case with a series motor.  If the series 
motor can handle the amps, it can handle the control. Not the case with 
sep-ex. 


David Roden - Akron, Ohio, USA
1991 Solectria Force 144vac
1991 Ford Escort Green/EV 128vdc
1979 General Engines ElectroPed 24vdc
1970 GE Elec-trak E15 36vdc
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