Re: (ET) Curtis controller mod

["Briggs, Michael" <Michael Briggs unh edu>]

I think that the problem with running in field weakened mode frequently is 
that the field weakening is accomplished by putting a resistor in series 
with the field coils. Any time you have additional resistance in there, 
you're wasting energy across it (like the toaster resistors). That's why I 
try to drive mine in third speed whenever possible - the toaster resistors 
are only used in the first two speeds, and field weakening doesn't start 
until the 4th one. 

So ideally the field weakening should only be used occasionally, not when 
doing active things (mowing, etc.).

Mike
________________________________
Michael S. Briggs, PhD
UNH Physics Department
(603) 862-2828
________________________________

________________________________________
From: David Roden <etpost drmm net>
Sent: Thursday, April 28, 2016 6:38 PM
To: elec-trak cosmos phy tufts edu
Subject: Re: (ET) Curtis controller mod

On 28 Apr 2016 at 10:51, Kim Petty wrote:

> I think I will end up mostly using the tractor in fieldweakened mode
> with 2 resistors in line and switching to full field voltage if I need
> it.

I'm not a motor expert, but I think I remember reading that most motors are
most efficient (I take this to mean less heat) at full field.  Normally you
use field weakening as a sort of overdrive.

That said, this may not be the case with the GE motor - it may be designed
for use with FW.

Maybe the motor experts here will weigh in on this.  Absent that coaching, 
I
think I would try to run the motor at full field most of the time.

PS - If I recall right, Mark Hanson built his own controller for an ET 
years
ago and used full field.  To get the higher top speed back (and probably
then some), he added 2 more batteries to the motor circuit for 48v.

Robert, your Curtis setup sounds good.  I think yours is the one I remember
reading about lo those many years ago.


David Roden - Akron, Ohio, USA

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