RE: Some thoughts about AC (was: For you, AC drive fans)

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

> -----Original Message-----
> From: owner-ev@listproc.sjsu.edu 
> [mailto:owner-ev@listproc.sjsu.edu] On Behalf Of Victor Tikhonov
> Sent: January 4, 2002 12:28 PM
> To: ev@listproc.sjsu.edu
> Subject: Some thoughts about AC (was: For you, AC drive fans)

[snip]

> Yes, that's why I prefer 336V cruising at 30A or even 660V 
> system and cruise at 15A rather than the systems with 
> thousands of amps and all the problems associated with it.

In all fairness, this is an argument for high pack voltages, not for AC
vs DC.  336V @30A is just 10kW.  You may cruise at this level, but your
batteries, controller and wiring need to be able to handle sustained
peaks of 5-10x this current if the vehicle is going to have acceptable
performance.  This situation holds true whether the motor is AC or DC.

A DC system with the capability of "thousands of amps" is most likely
going to put your AC system to shame in terms of power; they simply
aren't in the same class. so while there may be some problems specific
to (or more likely with) such high-powered systems, it really isn't an
apples to apples comparison.  Most DC street systems are in the 500-600A
(peak) category which is only about 2x the peak current capability of
your AC system (corresponding to the typical DC pack voltage of about
1/2 your AC system's).

[snip]

> But, as one fellow mentioned - AC system takes away the fun 
> of tinkering with brush advancing and other fussing with the system.
> 
> AC is boring like a Mac - you plug it and if designed right,
> it works forever, period. Nothing to do, no fireballs, copper 
> snots, welded contactors and other fun stuff. Well, not significant 
> disadvantage for me :-)

However, the fellow in question was referring to tinkering with an EV
used strictly for racing.  The vast majority of on-road EVs do not
require tinkering with brush advance or other fussing with the system.
How much brush advance tinkering and other fussing with the system did
your EV require when it was running as a DC system?  How much of that
was related to assembly issues (i.e. things you had to build or assemble
yourself vs things you bought off the shelf)?  How much of it can
honestly be said to be because of the motor & controller being DC
instead of AC rather than simple differences in manufacturing quality
between a $1500 DC motor and $800 Curtis controller vs an $8000
inverter/motor package?

Conversely, how much time have you spent tinkering with all of the
programmable options and features, etc. that your new AC system offers?
;^>

Don't misunderstand me, I am very excited about the prospect of
affordable AC systems, however, it really isn't fair to imply that the
benefits of high pack voltages are exclusive to AC systems, nor that the
liabilities of extremely high-powered DC systems are shared by modest
on-road DC systems.  I'd like to see a reliability comparison between a
typical DC system (e.g. 8" ADC & 500-600A Curtis or DCP on 144-156V) and
a comparably priced AC system of similar power.  And how about a cost
and reliability comparison between a 300-500kW+ racing DC system and a
comparable AC system?

Cheers,

Roger.