Re: why are EV DC propulsion motors all series wound?

[Robert McDonald <s348607@student.uq.edu.au>]

jim leuba wrote:
> 
> Dear EV list readers:
> 
> I need an EV education.
> Where can I read a technical discussion on propulsion motors?
> 
> DC motors with a separate field could easily provide regen.  Is there an
> efficiency loss when it is a motor (comparing separate field to series
> field)?  With field weakening, a separate field design has a wide (and
> energy efficient) speed range. 0-4000 rpm.
> 
> Where are brushless 3 phase AC (rotor is a magnet or electromagnet)
> propulsion designs?
> I read in the newspaper that GM uses a AC motor, made here in Dayton,
> OH.
> 
> My business is repairing CNC servo drives.  I am familiar with DC and AC
> spindle motors and drives.

Hi Jim,
This is a question I had when I first joined the list too!  I'm planning
to build an EV with a 3 phase AC induction motor, but the hitch is that
there are very few controllers for them that are suitable for EVs and
the ones that are suitable are way out of most peoples price range! 
That is why I want to design a controller that is simpler and
affordable, while being competitive with DC systems.

The reason most EVs seem to use series wound motors, is historic... all
the older controllers (not the relatively new, specialist ones from EVCL
and DCP, and maybe Auburn) were designed for forklifts or other
industrial applications.  There is no inherent reason for series wound
motors, other than that they seem to be readily available in a form
suitable for EVs...  Most off-the-shelf AC motors seem to be the totally
enclosed type, and hence too heavy for an EV, unless modified, and large
sep-ex DC motor controllers so far have been fairly scarce I think.  

Brushless DC and other AC types of motors all come down to cost and
niggling difficulties... but sep-ex DC or AC induction are the most
logical and elegant solution for 4 quadrant operating EVs, that is
certain!  If you know of a source of affordable, good quality sep-ex DC
motors AND controllers let us know!!!  I'm sure there'd be a bee hive of
interest!

As for technical discussion of traction motors... I'll try and dig a
bookmark or reference up...

Cheers,
Rob.