heh… As Christian mentioned - what does the nameplate say? A 2 pole motor is 3600RPM, 4 Pole is 1800RPM, 6 Pole 1200 RPM, 8 pole 900RPM at 60Hz. Those are your standard choices. At 10Hz the speeds would be 1/6 of those speeds or 600, 300, 200, or 150 ignoring slip. Squirrel cage motors (induction) come in a variety of slip categories (A,B,C,D) with different torque characteristics. Nameplate RPM’s will be slightly lower than the frequency/pole combination would indicate due to slip. Slip is the difference between the rotation rate of the stator versus the rotor. If the rotor where at the same speed as the stator there would be no current induced in the rotor, no magnetic field, and no torque. Slip varies by design category - typical is 2-7%.
Mark > On Mar 21, 2019, at 6:55 PM, [email protected] wrote: > > I have a gearmotor that I have bought for a new project. 3 phase. > I have a variable frequency drive for it. 120 VAC single input to 240 three > phase out. > Then I jack that up to 480 with a transformer. > > 10 Hz = 600 cycles per minute > Divide by 2 as there are 4 poles and I think that means 300 electrical cycles > per rotation (this is probably where I am going wrong) = 300 > Divide by 15 due to the gearbox 15:1 reduction and you get 20 RPM. But it > actually spins at 26 RPM. > > I was hand counting revs. > We did 5 Hz and got 13 RPM so I think the factor is more like 1.538 cycles > per rotation. > > 1.538 cycles per rev? > Where am I going wrong? > > Roughly 270 degrees per cycle? > Maybe that is it but I don’t know why. > > 10 Hz = 600 cycles per minute. > 600*270=162000 degrees per minute. > 162000/360=450 rpm > 450/15=30 rpm > Nope. > > So working backwards: > 26*15=390 motor RPM > 390*360=140400 degrees per minute. > > 140400/600=234 degrees per cycle > > I don’t recognize that as any kind of magic number... > -- > AF mailing list > [email protected] > http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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