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Re: (ET) controller
According to the Curtis 1244 manual (pp 36-37) at
http://www.curtisinstruments.com/index.cfm?fuseaction=cProducts.DownloadPDF&file=ACFWC9e9x1.pdf
the minimum field can range from 2 to 20 amps,
the maximum field can range from 7.5 to 60 amps.
This is off by an order of magnitude for what the ET motor needs. As
others have said, its field is around 2 amps *maximum*.
So I'm not sure how this controller could ever provide field weakening
with an Elec-Trak? And if it can't, may as well use a less expensive
series type controller for the armature only (if avoiding the Alltrax
sep-ex version for the ET).
While simple is generally good, and altering gear ratios is an
interesting approach to a higher top speed, eliminating the main
contactor makes me nervous. Curtis and all the other manufacturer's
suggested wiring diagrams always include a main contactor and any needed
pre-charge circuitry. The contactor is there as a safety to open up in
case the electronics fail, and MOSFETS have a habit of failing shorted,
as in full power on!
As for the "best" control system... Those who can correctly use the term
"l/h transition" in a sentence are likely able to install and repair a
system with discrete relays, while others like a single black box which
while more expensive to replace greatly reduces the number of parts to
deal with. Some care about field weakening, some don't.
So it all depends on the person.
Brian E. Haines wrote:
All of this does bring up a couple of more questions...
Would you recall what the field min/max you used with the curtis
controller? The 1244 allows from 0 to 20a min field, and 0 to .,...like
130a for the max field. Do you recall the field map?
Thanks
B
On 2/10/2011 6:06 PM, Clean Power Supply wrote:
I agree that the Curtis controllers used in this manner are quite
practical. And now I'll share my secret: I have top speed WITHOUT
weakening the field. I use a larger motor pulley with a smaller trans.
pulley, sized appropriately to achieve top speed with full field
voltage. Since speed control with an electronic controller is almost
infinite,losing the lower gearing is of no great consequence.
Additionally,I don't use *any* contactors,only a master disconnect
switch. The switch on the pot is used to turn the KSI (Key Switch
Input) on the controller on and off. A toggle switch with center off
is used to reverse the field polarity thereby achieving motor
reversal.The center off turns off the KSI,requiring the foot pedal to
be brought back to neutral to restart.This prevents slamming from F to
R while the motor is running and also gives a bit more time for the
field to collapse before polarity reverses.I do use a varistor to help
with that,though.
--
Jim Coate
*The Electric Tractor Store*
http://www.ElectricTractorStore.com
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