I manually counted it and it is 15:1 Nameplate says 4 poles. 1730 RPM on 60 cycles so that is about 4% slip at full power.
I guess I better measure the VFD frequency. From: Chuck McCown Sent: Friday, March 22, 2019 9:06 AM To: AnimalFarm Microwave Users Group Subject: Re: [AFMUG] OT VFD speed vs hz It is a pretty high quality gearmotor. I think it is made by oriental motor. I have the fan guard off and will manually count the gear reduction. Not sure what else it could be other than the VFD reporting Hz wrong. Maybe they are using metric Hz... From: Cameron Crum Sent: Friday, March 22, 2019 8:54 AM To: AnimalFarm Microwave Users Group Subject: Re: [AFMUG] OT VFD speed vs hz Are you sure the gear reduction box is a true 15:1 or is there some fudge factor there? On Thu, Mar 21, 2019 at 7:46 PM Forrest Christian (List Account) <[email protected]> wrote: Well that's irritating. Assuming the VFD is putting out the frequency you think it is, and that's a 4 pole motor, and the gearbox ratio is what you think it is, my math would agree with yours .... it should be putting out 2 RPM per Hertz. I mention the "assuming" part of all of the above because back in my industrial automation days I've seen nameplates not match reality on both gearboxes and motors. I don't remember what was different on the motor, but I've definitely seen a gearbox which wasn't the stamped ratio as I specifically remember hand cranking a gearbox and counting the input:output ratio and finding it different than the stamped ratio. I just remembered something else.... have you verified the motor is wired correctly? Sometimes a mis-wired or not-connected winding can do weird stuff like this. Depending on the motor it may also need to be wired differently for wye vs delta, etc. There is also always a bit of slip between the calculated RPM and the actual running RPM - induction motors have to run slower in order to develop torque., But this seems far enough out that this probably isn't it. On Thu, Mar 21, 2019 at 8:26 PM Chuck McCown <[email protected]> wrote: > > It has 4 poles printed on the nameplate. > > Sent from my iPhone > > > On Mar 21, 2019, at 6:15 PM, Forrest Christian (List Account) <[email protected]> wrote: > > > > What is the nameplate RPM and Hertz on this motor? > > > > Assuming a 4 pole motor, you'll have (frequency*120)/poles = RPM > > > > So if you have a 4 pole motor running at 10Hz, you'll find that it runs at 10*120/4 = 300 RPM After the 15:1 gearbox, you'd have 20 RPM at 10 Hz. > > > > It's linear so 2 RPM per HZ. So at 5 Hz you should get 10RPM. So you've got something off. > > > > Let's assume that you are just wrong with the poles. 26 RPM * 15 = 390RPM. Then, (10*120)/poles = 390. 1200/poles=390. Looks like it might be a 3 pole motor. > > > > Back the other way: > > > > 3 Pole Motor @ 10 hz = 10*120/3 = 400 rpm / 15:1 = 26.666 RPM. That's in the right range. > > > > Would 26.666RPM be in the range of your measurement/VFD accuracy? > > > > > > -- > > AF mailing list > > [email protected] > > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > > -- > AF mailing list > [email protected] > http://af.afmug.com/mailman/listinfo/af_af.afmug.com -- - Forrest -- AF mailing list [email protected] http://af.afmug.com/mailman/listinfo/af_af.afmug.com -------------------------------------------------------------------------------- -- AF mailing list [email protected] http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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