Larry Blanchard wrote:
On Thu, 11 Oct 2007 20:42:01 +0000, Nova wrote:


All of the machines you've listed would require a higher volume of air
flow than the shopvac can generate to be effective. A true 3 HP motor
would draw about 50 amps at 110V.


While I'd be he first to admit that HP ratings are usually bogus, I can't
see 5500 watts being required for 3 HP. With no power factor loss, one HP
is about 750 watts. That'd be 2250 watts for 3 HP. In real life, I'd
guess 3300 watts or so for 50 HP. That's about 30 amps.

Anyone have more info on actual average power factors?


Formula for a single phase motor:

HP = (E x I x Efficiency x Listed power factor)/746



Motor efficiency ratings can vary greatly. I'd expect the motor used on
a shop vac to be on the low end on the scale.

Common power factor ratings range from .70 to .98

See:
http://www.bacharach-training.com/norm/electric.htm

Or a web site to that estimates the values (I have no clue what %
efficiency and power factor they use):

http://www.shipcopumps.com/MathWizar...oramperage.asp

Example:

3 HP motor at 115V

Estimated Full Load Current
34A (amps)

Minimum Copper Wire Size
(75°C) THW, THHN-THWN, XHHW
8 Gauge

Magnetic Breaker Trip Rating
70A (amps)

Fused Disconnect
50A (amps)

At 110V the current would be higher than at 115V.

Even at 230V the start up current for a single phase 3 HP motor would be
in the area of 52 amps. The locked rotor current would be about 70 amps.

--
Jack Novak
Buffalo, NY - USA