Question about 3 phase motor

Josh Rider

Josh Rider

Stuff maker
Joined
Sep 2, 2014
Messages
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Right now im running a 1HP single phase motor with step pulleys on my kmg. It's been doing ok for the time being but I know I'm going to end up getting a 3 phase and vfd.
There is a leeson 3 phase 3HP im looking at right now but not sure if it is appropriate for a kmg and vfd.
It is a 145tc frame. Its also tefc. I know a 56 frame is recommended.
It's also continuous duty rather than farm duty.
would this work well or is it better used in something else?
Thanks!
 
Some like high HP for hogging, but they are in business and time is money


3HP will cost more in:
wiring the fuse panel to the machine
the VFD
you need new pulleys and wheels because the motor shaft is larger


Just use a 56 frame for "normal use"
 
Have a look at the motor frame dimensions chart:
http://kurz.com/wp-content/uploads/2014/09/Baldor-NEMA-Frame-Chart.pdf

Frame 56 is probably the most common small motor frame size, so stick with that to avoid having to get a different pulley, drill new mounting holes, and adding spacers for the different shaft height.

Continuous duty is what you want. "Farm Duty" is not really a thing -- Baldor and Leeson and a few others sometimes paste that on some of their motors, which tends to mean continuous duty with big bearings... but it doesn't have an official meaning as far as I'm aware. Look for a Continuous Duty TEFC motor of the same frame size as the one you're replacing, and it will be a drop-in replacement. On the motor's info tag, it should say Duty: Cont.; Encl: TEFC. You can also check the service factor, which should be 1.0 or preferable 1.15

3HP is fine AS LONG AS your VFD is rated to handle it AND you have the circuit in your shop to handle the extra amperage.
 
When I was young, all lawn mowers had 2-3HP motors. Now they have big engines. Maybe we had to walk a bit slower then, but they all cut the grass the same.
Any motor at or over 1HP will run a knife grinder. 3HP is way into overkill for anyone but a commercial shop. 1.5-2HP is the max most people will ever need.
 
Thanks for all the advice, I tried to research it before asking, but motors may as well be quantum physics to me:confused:.
 
Stacy has nailed it again - 3hp grinder is only required in a commercial level shop.

On the HP rating of lawnmowers - is it possible modern hp rating is a more of a marketing number rather than an engineering number? Just think of the shop vacuums with a 4hp rating and run on 110vac {g}

Ken H>
 
Yes, I know that electric motor ratings can be widely overstated on things like routers and shop vacs. That is due to some fuzzy and misleading math they apply because those motors run at higher RPM than standard 1750RPM motors.

To get a feel of how powerful a motor is, look at the amperage.... volts X amps = watts consumed. 746 watts is 1 HP of output power at the shaft. In actual use on a motor, there is loss of electrical efficiency, as well as mechanical loss..... so the wattage used will be higher than the watts of power delivered. A look at the efficiency rating of the motor plate will show how efficient it is. They normally ranges from 65% to 85%. The more efficient, the more power you get for the same amount of electricity, and the less current it will draw for the same 1HP of power delivered. I usually figure that an efficient 1HP motor uses about 10 amps and an inefficient one uses about 14 amps. It becomes clear by that knowledge that no shop vac delivers 5HP on a 16 gauge cord plugged into a 120VAC wall outlet.

About lawn mowers - I think the gas motors were smaller back then because the mowers were smaller, lighter, and simpler. No heavy frames, no big wheels, no electric starters. no power driven wheels....etc. All they needed to do was turn an 18-20" blade in a circle. Heck, the first several mowers I used didn't have a re-coil starter. You wound the rope around the top pulley and gave it a yank.
 
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