Horsepower | Cypress Semiconductor
November 06, 2011
I have been looking a Shop VACs and air compressors this last couple of weeks and I am getting pretty tired at the speced horsepower ratings. At least industrial compressors are a bit more honest.
One horsepower (HP) is 746 watts. For 120VAC and with a typical efficiency of 67% to 75% you would expect a current draw of somewhere around 8 to 9 amps per HP, maybe 10. So how do they get to call a motor with a 10 amp draw 4 peak horsepower? Well it turns out that UL does not measure a motor’s power by HP. They use current draw.
A word of warning! If you go to Wal-Mart and put yellow post-its on their Shop VACs and leaf blowers with the real HP rating, they will not find it a bit helpful and you will be asked to leave. Really an overeaction, its not like I used a big marker to write directly on the boxes. (I have been thrown out of far better places than that!) No good deed goes unpunished.