On Monday 25 January 2016 14:48:49 John Kasunich wrote: > On Mon, Jan 25, 2016, at 02:17 PM, Gene Heskett wrote: > > Even unloaded, the slippage is usually north of 20 rpm & quite > > visible. > > Guess that depends on the motor. > > Modern industrial size (1HP and up) three-phase high efficiency > induction motors often have rated speeds of 1780 or 1785 RPM, > four-pole 60Hz. > > That means that slip at full load is 15 or 20 RPM. Slip is fairly > linear with load, so a 10HP motor spinning nothing but its own cooling > fans can easily have less than 1 RPM of slip.
That is for 3 phase John, which is considerably more efficient. On single phase with a running capacitor on the 2nd winding, it will be worse, and the common ones that have a starting winding, leaving a single winding once speed has been achieved, 1750 is about tops, and often closer to 1725 for the fractional horse stuff. But as you note, a 10hp is big enough people pay attention to the power meter's rpms, so they are usually quite a bit better. At a no load idle, a 100HP might draw only 4x what a 10HP does in my observations. That I believe translates directly to a lower "slippage" at no load. I often judged how well a fan system or a cooling water pump was being loaded by measuring amps on a phase, if its pulling right at the nameplate FLA, then I have the pulley ratios correct. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Site24x7 APM Insight: Get Deep Visibility into Application Performance APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month Monitor end-to-end web transactions and take corrective actions now Troubleshoot faster and improve end-user experience. Signup Now! http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
