RE: 1-O-X revolutionary digital EV motor

["Roger Stockton" <rstockton@delta-q.com>]

> -----Original Message-----
> From: owner-ev@listproc.sjsu.edu
> [mailto:owner-ev@listproc.sjsu.edu] On Behalf Of VanDerWal, Peter
> Sent: October 31, 2001 2:22 PM
> To: 'EV List'
> Subject: Re: 1-O-X revolutionary digital EV motor

[snip]

> The problem is, you are looking graphs of how the motor
> performs at full operation voltage.  Chances are when you are 
> cruising around at 10 mph, you're not going to be cramming 
> full pack voltage into the motor.
> 
> For DC motors the charts change, with the max efficiency
> point moving towards zero RPM, as you reduce voltage.  
> Granted the max efficiency drops at lower voltage, but it's 
> still going to be better than what you're reading off the 
> full voltage chart.
> 
> For AC motors things get really hard to tell since they
> change voltage, frequency, phase angel, etc, etc.

Yes, you have a very good point; the picture may look quite a bit
different at low speed than the graphs we've seen suggest.  I'm not sure
how the AC graphs could *not* have taken this into account, as the
efficiency map *is* a 3D plot of efficiency plotted on axes of power vs
RPM and I'm not sure how one could reach a point shown on the efficiency
map that is below the full power boundary at a low RPM unless the
inverter was already making all the necessary
voltage/frequency/phase/etc. adjustments required to operate at that
point.

Typical DC graphs only depict a single curve of efficiency vs torque or
RPM for a specified voltage, and so I can certainly appreciate that the
efficiency curve at some other voltage may vary significantly.  However,
in all cases the efficiency at 0RPM is fixed at 0% so the curve will
always have low efficiency values at low RPM, and if the peak efficiency
is dropping at the same time as it shifts to lower RPM then it is
entirely possible that the curve actually changes very little at low RPM
despite changes in voltage.

Cheers,

Roger.