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
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
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.
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
Est. yearly US cost to safeguard Persian Gulf oil supply: $50 billion
Est. 2001 value of US crude oil imports from Persian Gulf: $19 billion
-- Harper's Index, April 2002
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
_______________________________________________
Elec-trak mailing list
Elec-trak cosmos phy tufts edu
https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak
_______________________________________________
Elec-trak mailing list
Elec-trak cosmos phy tufts edu
https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak