Motor Horsepower

Sounds right to me.

i

If you're trying to figure out how much HP is being produced at the shaft you also need to account for power factor. A typical small induction motor will draw around 60% of its nameplate current with

*no* load.

80% efficiency sounds high for a 2HP single phase motor. Full load amps for a normal 2HP induction motor is closer to 25A @ 120V.

Pretty close for 16 amp running current - but how much does it draw on startup??? Most motors that will draw 16 amps on startup will draw closer to 7 under normal running conditions - which is 1 HP. Not 2 many real 2HP motors will start on a standard 15 amp breaker or fuse, and many will not start on a standard 20 amp breaker or fuse. A

20 amp slow-blow fuse will GENERALLY start a 2HP motor under a reasonable(light) load like an unloaded compressor or a 10" table saw.

I also mostly agree based on a chart I have here.

2 HP AO smith 120V motor pulls: 16.4 to 16.6 at 3600 RPM 17 to 17.8 for 1800 RPM

Thanks Iggy, I appreciate that.

Jon

Thanks Joe, that is in line with my measurements as well.

Jon

That must be a capacitor start/capacitor run motor, not a more typical cap start. The run capacitor improves the power factor, lowering the line current.

Unless you measure the current with a phase-sensitive ammeter, you are measuring two totally unrelated values. The problem with AC (I'm assuming from "120 V" that this is an AC motor) is that the phase angle is extremely important. Many motors will have only a small variation in measured current from no-load to full load. the difference is that the phase angle between voltage and current shifts dramatically from no load (current lags nearly 90 degrees from voltage) to full load, where current and voltage are nearly in phase. The POWER drawn changes just as dramatically, from maybe 200 Watts to 1900 W. But, you will likely see a 2 HP motor will draw 11 - 13 A at idle.

Jon