formula for wattage required for various electric motors

thanks all. I will use 1000 watts/hp and 3x for my general use.
bumpy

Bumpy: 3x for starting inductive loads (motors) will be adequate for anything in an RV. Most startup loads will be less than that but things like AirCond, Hair dryers, and such can pull that much. It's a general thumb rule but works very well for sizing power supplies

The 746 Watts per HP is a direct 100% efficiency translation.. Alas.. you won't get 100% so a better "Rule of thumb" is 1,000 watts per HP. (Old design manual I read in high school, sorry no web back then to link to).

And then you need to consider what it takes to kick start that motor.. I have seen 5,000 watt draw for a very short time when starting.

Place I worked had a couple of BiG and I MEAN BIG!!! Series wound motors (the kind that draw like 200 amps at 440 volts) Well the meter went to 400 amps.

Someone shoved the switch from OFF to RUN without first pulling it to START (Which bypassed the meter) and the needle really did wrap it self around the 500 amp PIN .

After that the new owners put in an auto start system .

hmknightnc wrote:

Chris Bryant wrote:
Those numbers are fine if your motor is 100% efficient, but really should not be used for spec'ing in the real world.

That's true enough. I always just make it simple. 1hp=1kw running and 3x starting

Oh thanks for mentioning start up draw. is 3 x a reasonable number to use?
bumpy

Chris Bryant wrote:
Those numbers are fine if your motor is 100% efficient, but really should not be used for spec'ing in the real world.

That's true enough. I always just make it simple. 1hp=1kw running and 3x starting

Chris Bryant wrote:
Those numbers are fine if your motor is 100% efficient, but really should not be used for spec'ing in the real world.

X-2
Very misleading compared to real world.

Those numbers are fine if your motor is 100% efficient, but really should not be used for spec'ing in the real world.

2hp= 2*746 = 1492w
1/4hp = 746/4 = 186.5w

thanks guys
bumpy