RE: (ET) Solid state controls

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

On 23 Jul 2002 at 14:51, Elie, Larry (L.D.) wrote:

> Most PWM controllers use 200 to 2000 Hz (cycles/sec) so that the period 
> of
> each pulse is less than the inductive time constant of the coil. 

True of SCR designs and most older bipolar transistor controllers.  

However, most golf car controllers today use MOSFETS and chop at 15 KHz 
and 
above to keep the inevitable noise from the motor inaudible.  This makes 
low 
speed control much less smooth, though, because of the ridiculously short 
on 
time at 10% duty cycle or less.  As I understand it, depending on the 
motor 
inductance, in many cases the current limit circuit actually can't react 
fast enough.  So some of the larger controllers actually switch down to 
1.5 
or 2 KHz at low duty cycle.

> I have yet to see a PWM control for this
> class of vehicle that also implements field-weakening.

Curtis makes some true sep-ex golf car / industrial vehicle controllers 
which I'm pretty sure do implement field weakening.  I could be wrong 
about 
this though.


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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