Re: What is the typical amperage draw of the field for a sepex motor?
Jeff Major wrote:
> IIRC, 37 percent increase in resistance was 120 degree
> C rise. This is what could be used on a class H
What I use is Thot = Tcold + (K x ((Rhot - Rcold) / Rcold))
where K = 256.4 for copper
Thot = hot temperature in deg.C
Tcold = cold temperature in deg.C
Rhot = resistance at hot temperature in ohms
Rcold = resistance at cold temperature in ohms
> Also, he should have the appropriate ventilation during the test.
Yes; run whatever blower or airflow the motor would normally have had.
The easiest way to do such a test is to actually run the motor on the
bench at its normal RPM, so its internal fan (if so equipped) is working
normally. Measure the field resistance when cold (at room temperature)
before you start, and again after running the motor for a while.
> A few years ago, I came across a smaller sepex GE
> motor with a private brand nameplate, so I figured I
> was on my own to figure out how to control it. Also
> had a freebie Curtis sepex with a custom software. I
> was able to adjust field map parameters, but needed
> motor info. So I ran a no load magnetization curve
> and was able to tell when it saturated and how far
> down to field weaken it. Very helpful.
That's a good idea, too. Run the motor and keep increasing the field
strength, noting the RPM decrease it causes. The field is saturating
when 10% more field current only reduces RPM by (say) 5%.
I've often thought one could build a pretty handy motor "characterizer"
with nothing but a battery pack, on/off contactor, and free-spinning
motor. Use a computer with some simple instrumentation to measure
voltage, current and RPM. The software would switch on the motor, and
measure its power as it speeds up. The motor's own inertia forms the load.
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in -- Leonard Cohen
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net