Calculating electric motor HP from watts/amps?

[Dan]

I know there's a formula for this, but the only ones I can find online
require a figure for efficiency. Maybe this is simply assumed? If so,
I'm not sure what level of efficiency to use. Motor in question is on a
power saw, rated 120V 60HZ 1800 watts 4100RPM. Anyone know this?

TIA

Dan

 

[Beloved Leader]

I know there's a formula for this,

1 hp = 746 watts. A 100 hp motor is 75 kw. A 200 hp motor is 150 kw.

 

[Dave Plowman (News)]

I know there's a formula for this, but the only ones I can find online
require a figure for efficiency. Maybe this is simply assumed? If so,
I'm not sure what level of efficiency to use. Motor in question is on a
power saw, rated 120V 60HZ 1800 watts 4100RPM. Anyone know this?

Looks like a 2 hp to me. 746 watts per horsepower at 82% efficiency sounds
about right.

 

[Peter Duck]

In message <[email protected]>

I know there's a formula for this, but the only ones I can find online
require a figure for efficiency. Maybe this is simply assumed? If so,
I'm not sure what level of efficiency to use. Motor in question is on a
power saw, rated 120V 60HZ 1800 watts 4100RPM. Anyone know this?

1800w equates to 2.41HP: as motors are generally built to nominally
'exact' horse-powers (smaller ones to such fractions as 1/4 or 1/2), I'd
think it pretty safe, for practical purposes, to assume this one to be
'2 HP'.

That would make the 'efficiency' 83% - quite plausible for such size.