Oh, not another AC-DC war again!

[Victor Tikhonov <vtikhono@lsil.com>]

Roger Stockton wrote:
> 
> > -----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.

No Roger, 5x-10x doesn't have to be *sustained* - just for duration of
acceleration. You know that. And during acceleration the wiring
is allowed to be a bit warmer.

Also why no one then runs (or makes) 9" ADC for 336V? Everyone wants to 
cut I2R losses!
> 
> 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.

Please give me a single example of the "same class" DC motor - 
liquid cooled and having the same torque at 7000 rpm as at 0 rpm.

Raw power? At what RPM? I'm not into racing, but if you install
the same rated (name plate) power motors (AC and DC) in two vehicles
and all else be equal, you know which one will finish first -
the one with more torque at the wheels all the way, means one
you don't switch gears on.

> 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? 

A lot! I installed my brand new 8" motor as it was shipped to me, and in
first
 5 miles it burned the brushes and ruined the commutator. Turn out that
unlike other cars on Hondas the motor shaft rotates CW, but default
plate advance
is made for CCW. No one mentioned that, and I always thought that DC
motors are
symmetric. Expensive mistake, exactly because of brush advancing. I'm
sure I
am not the only one discovered it hard way.

Another issue - throttle pot linkage. Mechanical adjustments for correct
wiper
travel are not particularly easy.

> 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?

You get what you pay for, but I see your point.
 
> Conversely, how much time have you spent tinkering with all of the
> programmable options and features, etc. that your new AC system offers?
> ;^>

None if I don't want to - defaults are good for typical user.
Tweaking improves something, but totally optional.
 
> 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.

I understand you Roger, and also exposing my view on the issue, even if
it seem biased. The purpose of the discussion is not to prove who is
right
or wrong, but to get objective info to everybody so they are more
informed
and educated so can make decisions better reflecting their needs.
People will only benefit from knowing all cons and pros, after all
we all in the same boat and promoting EV in general. That's most
important.

Both systems have their uses and both are here to stay, that's clear.

Regarding reliability I can't speak for other systems as I have no data.
First Siemens systems (the same model I have available now) were
installed in VW Golfs back in 1992, and as my supplier reported,
still work today, no problem. The warranty is the best reflection of
expected reliability a manufacturer knows about.

We offer 10 years warranty regardless of the application, racing or not.
Please point me to a single controller manufacturer coming close.
To be fair, it's not AC vs DC issue, there are crap AC inverters made
in sweat shops by slave labor. Again, you get what you pay for, and
I'm sure my system will outlive my car and likely migrate to a next one.

Victor