Re: (ET) E12S and a curtis controller??

["Steve Richardson" <scr echoweb net>]

David you make some really good points.  My ET pours out the heat when it's
running along, mabey mine just has a problem !  As I understand the "Theory
discussion" I had with Damon the controller will weaken the field with a
light load and pedal-to-the-metal.  If the load increases then the
controller will increase the field current to compensate.  This is really
more to protest the armature than to control speed.  If the field is too
weak with a given load then the armature current may rise to high.

 We have no experience with the GE ET.  But it's still just a sep-x motor..
The controller is really being designed for Golf Cars, which have larger
motors and higher currents than the ET's.  So the controller will actually
be little more than is required for the ET motor.

I look forward to testing in my ET with the new controller.

I appreciate all this input.  It helps us make a better product..

Thanks David and all..


--- Original Message -----
From: "David Roden (Akron OH USA)" <roden ald net>
To: <elec-trak cosmos phy tufts edu>
Sent: Friday, June 27, 2003 10:15 PM
Subject: Re: (ET) E12S and a curtis controller??


> On 27 Jun 2003 at 17:51, Steve Richardson wrote:
>
> > The Alltrax controller automatically adjust the field strength to keep
it
> > within a percentage of the of the armature current.
>
> I take it that means it will ^not^ perform field weakening based on pedal
> position. Too bad. Our GE motor was designed to use field weakening
(though
> obviously it doesn't require it).  I'd like to retain FW on mine. Others
may
> feel differently, of course.
>
>
> > We believe the tractors will probably see an increase in top ground
speed
> > because of the efficiency of the controller over the GE control
> > system.
>
> With the GE, top speed (before field weakening) is with the battery
> connected directly to the motor.  I don't see how you can get any more
> efficient than that!  Semiconductors always have a forward voltage drop.
> Unless you have a bypass contactor, I think you'll find your non-FW top
> speed is slightly ^lower^ than the original speed (assuming 36 volts).
Not
> that it would be a big deal.
>
>
> >  Another option, one I'm going to try, is use a 48v battery pack ...
>
> Mark Hanson did that with his homebrew ET controller.  He just dropped in
> some 8 volt golf car batteries.  He didn't use FW either, and said the
> higher voltage just about made up for the loss of top speed.
>
> There are some problems with using 8v batteries though.
>
> First, you'd probably need some way to derive 36 volts for the mower deck
> and other accessories.   Mark built a separate controller just for that
> purpose.  He's a pretty smart engineer, so if he felt it was necessary 
> I'm
> not about to try running my mower deck on 48 bolts.
>
> Second, you'd also need a DC:DC to run the lights -- 8v is too low, 16v 
> is
> too high.  So figure more $$$ for that, though it's a good idea anyway.
You
> might be able to get away with just a simple regulator circuit (unless
> you're worried about wasting the energy as heat).
>
> Third, you'd need a different charger.  Again perhaps a good thing as the
> original is kind of brutish -- but I suspect few users will be very
> interested in this kind of investment.
>
> I'm sure the lift will work fine on 16 volts, so no problem there.
>
> An alternative to the 8v golf car batteries is to use four smaller 12
marine
> batteries instead of 6 golf car batteries.  Then you could retain pack
> tapping (but still need a new charger).  Downside is that you'd lose 
> cycle
> life with those batteries.  Range also might then become a problem,
> depending on the user's needs.
>
> Maybe you could configure the controller as a buck/boost type.  Then the
> user could use 36 volts input, and get 0 to 48 volts at the motor.  I
don't
> know how much this might add to the cost.
>
>
> > The field weakening
> > method used on the Elec-Trac's is to insert resistance in series with
the
> > field winding which turns a lot of energy into heat. A modern 
> > controller
uses
> > PWM to create varying voltages for the field, creating very little 
> > heat.
>
> The field current is fairly low, so IMO the amount of loss from the ET's
> resistive field control is trivial.  The loss from the resistive armature
> control is much, much more significant.
>
> But even at that, I hear relatively few complaints about limited range or
> inefficiency on this list.  I may be mistaken, but I think most
experienced
> ET users know enough to pick a gear that allows them to run the tractor
most
> of the time with the armature resistors out of the circuit.
>
> The main reason I want a "real" controller is to get fine control without
> having to shift into LL.  Range isn't an issue for me.  The stock ET has
> plenty of range for my needs, even with lower battery capacity than was
> standard.  I currently use East Penn 8G24 group 24 gel batteries (6 in
> series-parallel), and I've never come close to running them flat.  But,
> again, others might benefit from increased range.
>
>
> David Roden - Akron, Ohio, USA
> 1991 Solectria Force 144vac
> 1991 Ford Escort Green/EV 128vdc
> 1970 GE Elec-trak E15 36vdc
> 1974 Avco New Idea 36vdc
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