Well I always prefer to use metric crescent wrenches. Drives me nuts when I get a standard one instead.
On Fri, Mar 22, 2019 at 10:43 AM Bill Prince <[email protected]> wrote: > Oh yeah. Those metric hertz will get you every time. What the heck was > wrong with Imperial hertz anyway? > > Get off my lawn! > > > bp > <part15sbs{at}gmail{dot}com> > > > On 3/22/2019 8:06 AM, Chuck McCown wrote: > > 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 > > -- > AF mailing list > [email protected] > http://af.afmug.com/mailman/listinfo/af_af.afmug.com >
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