Re: (ET) Electronic controller

["RJ Kanary" <rjkanary nauticom net>]

I am not an EE, nor do I play one on television. My understanding of the
"series " field, is that it exist to cancel the bad effects of phenomenon
known as Armature Reaction. Not having the text book here right now 
deprives
me of detail. But the existence of this winding is what allows the traction
motor to provide equal torque, in both directions, and allows higher
armature speeds, when the field is weakened, without the loss of efficiency
that would be the result of Armature Reaction. If anyone could fill in the
numerous blanks that I have left, or has information to refute my poor
memory, feel free to do so. <G>


RJ Kanary @ Bandi Bros. Inc.
Member TRNi  Since 1998
ASE® Certified Master Auto Technician
Member Tech Line Associates Since 1987
rjkanary nauticom net

----- Original Message -----
From: "Bob Murcek" <rmurcek geisinger edu>
To: <roden ald net>; <elec-trak cosmos phy tufts edu>
Sent: Wednesday, January 09, 2002 22:48
Subject: Re: (ET) Electronic controller


> Yep, my E12 motor is definitely compound, but I wouldn't have known that
if I hadn't had to replace its bearings since the series field is 
internally
wired is series with the armature.  (Ordinarily the leads for a series 
field
would be externally accessible so that the series field could be reversed
when reversing the motor.)
>
> The presence of the series field somewhat reduces the danger of the shunt
field not being excited.  I haven't tried it, but I suspect that without 
the
shunt field the motor speed would be very unstable, like a sewing machine.
I do paranoidly have things arranged so that full power is applied to the
shunt field as soon as the tractor is powered up, though.
>
> Since the PWM controller provides fully variable control, and since the
thing is plenty fast enough for my purposes in 4th, I haven't done anything
with field weakening.
>
> The deal with the series field not being reversed when the motor is
reversed seems weird to me.  This implies that the shunt field is much
stronger than the series field and can therefore overwhelm the series field
to reverse the motor.  This probably means that the tractor doesn't have as
much torque in reverse as it does in forward.  Another indication that the
shunt field is stronger is that I do feel substantial regenerative braking;
ordinarily a series field would reduce this effect.  I'm wondering if a 
weak
series field was added just to provide extra oomph when starting out under
heavy load, like plowing.  Anyone know if that's a common motor design
practice?
>
> Overall the series field is so weak that the motor behaves similarly to a
PM motor.
>
> >>> "David Roden (Akron OH USA)" <roden ald net> 1/9/2002 1:03:19 AM >>>
> On 9 Jan 2002 at 0:47, David Roden (Akron OH USA) wrote:
>
> > The only cautionary note I would sound in using a controller intended
for
> > a PM motor is you should probably have some kind ot switching system
that
> > ensures that the field is always energized ~before~ voltage is applied
to
> > the armature, and that the field is always shut down ~after~ voltage is
> > removed from the armature.  (This might not be so important with a
> > compound motor, but it's still a reasonable precaution.)
>
> And just a little while later I ran across this comment about separately
> excited motors on the EV mailing list:
>
> = + = + = + = + = + = + = + = + = + = + = + = +
>
> ... you have to be very careful in controlling a sep-ex motor, especially
> at high voltage.  The motor is the inductor, but it looks like a SHORT
> CIRCUIT without the field energized properly first.
>
> Without interpoles you have to be extra careful with field weakening.
> (even with interpoles you have to be careful).
>
> If you keep the field energized to an appropriate level, this won't be a
> problem.  But the gray area is how far you can field weaken without
> creating a fireworks show on the commutator.
>
> I guess this is why sep-ex has never been very popular in the EV hobbyist
> community.  You really have to [know] the motors capabilities or have a
> pretty good controller.  This is not real difficult, but there are very
> few control vendors that offer a good sep-ex control.
>
> The other problem is that the sep-ex control should be matched with the
> motor.  This is not always the case with a series motor.  If the series
> motor can handle the amps, it can handle the control. Not the case with
> sep-ex.
>
>
> David Roden - Akron, Ohio, USA
> 1991 Solectria Force 144vac
> 1991 Ford Escort Green/EV 128vdc
> 1979 General Engines ElectroPed 24vdc
> 1970 GE Elec-trak E15 36vdc
> = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
> Thou shalt not send me any thing which says unto thee, "send this to all
> thou knowest."  Neither shalt thou send me any spam, lest I smite thee.
> = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
>
>
>