RE: Oh, not another AC-DC war again!

["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 4:10 PM
> To: ev@listproc.sjsu.edu
> Subject: Oh, not another AC-DC war again!

[snip]

> 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.

Depends on your definition of "sustained".  I used the term to
distinguish between  an instantaneous peak condition and a condition
that might easily endure for several tens of seconds (e.g. climbing a
long hill, etc. where your EV will need much more than 10kW from the
batteries to keep up with traffic at highway speeds).  Yes, acceleration
peaks might only have a duration of about 10seconds, but they are hardly
the only condition when your pack will be required to handle much higher
currents than you suggest.

> 
> 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.

Cooling mechanism is not a determinant of "class" in the context of this
discussion.  You were criticising DC systems as unreliable and
problematic due to their need to handle "thousands of amps"; I am making
the point that very few of our DC EVs deal with thousands of amps
outside of racing vehicles, and it is hardly useful to point to a
300-500kW DC racing system and exclaim "HA, see it is less reliable and
more problematic than my 30kW AC system, therefore AC is superior".
Same "class" in this context is same power level.

> 
> 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.

"More torque at the wheels all the way"?  If you mean the one that makes
more torque at every RPM than the other, then I agree completely...
however, the motor that makes more torque at every RPM than the other
must by definition have a higher nameplate rating, so this can't be what
you mean.  Probably you mean the one that makes a more consistent level
of torque at all RPM (since this is a desirable atrribute of AC systems,
and you favour AC systems).  In this case, and assuming we are talking
about drag racing, I will disagree with you.  The car that has more
torque at the wheels at higher RPM may well finish the race at a higher
speed than the other car, while the car with more torque at lower RPM
may still reach the finish line first and win the race.  

[snip]

> 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.

I suspected you might say this, seeing as you converted a Honda.  It
could be argued that having to set the brush advance properly is
specific to DC systems, and therefore this is a "DC system" problem,
however, it could also be argued that  this was a user problem as it is
specific to the conversion of a Honda and 99% of EV converters would not
have had to fiddle with the brush timing at all.

In any event, I specifically asked about the amount of fiddling your DC
system required *once running*; that is, the problem you describe is due
to a mistake made during the conversion/motor installation.  Once you
installed the motor correctly for your atypical vehicle how much
fiddling was *required* with the brush timing or other aspects specific
to the DC system?

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

And your AC system also has a mechanical throttle pot and linkage.
Despite purchasing an expensive purpose-made pot you still had to
fabricate a bracket and modify the lever on the throttle pot, and then
program the controller to recognise the min and max settings.  Yes,
being able to program the min and max settings makes the process a
little easier than having to get the mechanical linkage just right (as
required, say by a Curtis controller), however, this is *not* an AC vs
DC comparison, just one manufacturer's product being easier to setup
than the other.  Consider a DCP controller's inductive throttle "pot"
setup: even easier to install and calibrate than your AC system's
throttle pot (no need to modify levers, etc.); does this make DC systems
superior to AC?  Of course not, but it makes the DCP controller's ease
of installation superior to the Curtis', just as the Siemens inverter's
is.

[snip]

> > 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.

Yes, and my point is that there is very little tweaking and fussing that
I *need* to do with a DC system either; the defaults are good for the
typical user.  If you happen to be an atypical user (e.g. converting a
Honda), then you may have to set your brush timing appropriately; the
rest of us don't.  I may choose to continuously fiddle with my brush
timing just because I want to, just as you may choose to fiddle with
your inverter's settings, however, the defaults are good for the typical
user and there is no *need* to fiddle if you or I don't want to.

[snip]

> 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.

Absolutely, and this is why I take issue with the implication that only
AC systems can allow the benefit of high pack voltages to be realised,
or that all DC systems *must* handle thousands of amps and are therefore
more problem prone and unreliable than a lower current AC system.  High
voltage DC systems do exist and reap the same benefits from the reduced
current draws as do AC systems.  DC systems commonly have pack voltages
around 1/2 that common to AC systems and will therefore need to handle
currents about 2x those that the AC system does since the vehicles will
tend to be the same weight and require the same power to move down the
road.  This is a far cry from the implication that an AC system requires
only 30A while DC systems require "thousands".

[snip]

> 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.

How many Golfs were built with these systems, and are they in the hands
of the public or just part of some limited trial or research project?

> 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.

The warranty duration is a hint, but that is all.  It indicates the
manufacturer's confidence in the product in its intended application.
You offer a 10 year warranty even in racing use, but how many units do
your customers have in the field and how many of those are actually
seeing racing duty?  The warranty period will be a lot more meaningful
when we actually see people subjecting the product to the stresses of
racing without breaking it and still being competitive.

[snip]

> Again, you get what you pay for, and I'm sure my 
> system will outlive my car and likely migrate to a next one.

Just as many DC systems have outlived their original conversion vehicle
and will continue to do so.  I recently sold an EV that was originally
converted 20 years ago and its DC motor and controller were still
perfectly usable.  Of course, the SCR controller is now regarded as
undesirable compared to high-frequency MOSFET and IGBT designs, just as
your AC inverter will likely be considered outdated relative to the
designs of 10-20yrs into the future.  However, it may still be perfectly
usable, just as my SCR controller was...

There is no war.

Cheers,

Roger.