Re: what is the max bus voltage, 300V?

[Rod Hower <rodhower@ameritech.net>]

Lee is correct about the bungling on this motor.
I have always suspected there is a design flaw.
Regardless, a Sepex motor relies on field weakening
to get high RPM's.  It is also easy to regen with a
sepex motor.  One thing that is a problem with sepex
motors is the inability to change brush advance.
This is a big problem when operating over a wide
torque speed curve and a bigger problem when you try
to regen (when the brushes would rather be at a different
orientation than motoring).
The major advantage of the AC motor is the control can
effectively change brush timing (OK, there isn't brushes,
but electrically its the same).
So a properly designed AC system does have an advantage over
the DC since the motors peak performance point can be optimized
better with the electronic controller.  I'll admit that there
may be design problems with the GE sepex motor, but it still
cannot produce the wide torque speed curve of an AC control system
unless it has a mechanical assembly that can change brush advance.
I may not get an "agree" from Lee on this, but I would like to
compare how a sepex design without moveable brushes can match
the performance of an AC system.
Rod

Lee Hart wrote:
> Dave Davidson wrote:
> 
>>My TEVan uses SEPEX at 180 volts... Chrysler really kept the power
>>down and the van is really slow.
> 
> 
> Yes; something is wrong with GE's motor design. GE certainly knows (or
> used to know) how to design large DC motors to work reliably, but they
> bungled this one somehow.
> 
> 
>>I believe series DC came about for hobbyists because the industrial
>>EVs have historically been series DC. It was a simple matter to adapt
>>to a car and then they started increasing the voltage and power.
>>A series DC system can be made very simple and relatively inexpensive.
> 
> 
> Agreed (see, I *can* say it, Victor :-)
> 
> 
>>I believe the reason high voltage AC systems were chosen was because
>>the engineers were familiar with industrial drives, which are at
>>least 208 volts three phase. It was probably not difficult to adapt
>>an industrial drive to a vehicle.
> 
> 
> Again I agree. This is a good description of what I meant by
> "fashionable" designs; picking a design based what is already available
> and what everyone else is doing.
> 
> 
>>If you designed a DC system to have all the whistles and bells that
>>current AC systems have, it would likely be just as expensive but
>>without the advantages of AC.
> 
> 
> I don't think this is true. Most of the cost in a motor controller is in
> the power semiconductors and cooling. AC drives have a lot more silicon,
> and so are a lot more expensive. The control electronics cost very
> littl, and with microcomputers, you can have a very large feature set at
> low cost.