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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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