Re: (ET) controller

[David Brandt <ev_dave13 yahoo com>]

Well said, Jim.  I absolutely agree, and incorporated all the same safety 
circuits on my curtis powered ET that existed on the factory version.  It 
was more effort, takes more parts, and more work and expense to do up 
front, but it pays for itself the first time you avoid an unsafe situation.

David Brandt


--- On Wed, 2/16/11, Jim Coate <jbc_lists_NO_REPLY coate org> wrote:

> From: Jim Coate <jbc_lists_NO_REPLY coate org>
> Subject: Re: (ET) controller
> To: "Elec-Trak" <elec-trak cosmos phy tufts edu>
> Date: Wednesday, February 16, 2011, 10:25 PM
> 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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