Electric Motors :: Not For Air Compressor Use

abrace

Registered
Registered
Joined
Dec 25, 2015
Messages
214
All,

I was looking th the Grizzly catalog today and their electric motors. They all have a disclaimer in the description that says 'Not for Air Compressor Use'. I know a compressor puts some unique strains on a motor, especially when the tank is partially full and the motor fires on and the compressor doesn't have an unloader valve, or it is stuck. That said, I am no motor expert and am curious. What is it about air compressor use that makes these Grizzly motors unsuitable? As long as you pick a motor with the right horsepower, why wouldn't it work?
 
Good question and I believe it has to do with starting torque, especially when the pressurestat is set to restart with only a slight drop in tank pressure.
Mark S.
 
another consideration is operation temperature.
air compressor motors are usually rated for continuous use
 
Two biggest issues with a compressor are high starting load and run time.
For the average Joe and his garage compressor. He airs up bike tires for his kids. Occasionally will add air to a car tire and once in a while he will use his handy blow gun things as he refers to it to dust off his garage floor when his buddies are coming over to drink beer.

then you have clowns like us.
We fire up a compressor and will connect air die grinders to it and run it for hours as we knock off welds, polish and surface parts we have just machined. Blow the swarf (bad idea) off our mill. Connect it up to our plasma cutter and cut out parts. Then its back to the die grinder to clean up the edges. And the hole time the compressor is pumping away. If not continuously very close to it. Machinists use a ton of air in the shop. We really don't even think about it if we have a big enough compressor. If we don't, then we notice as we are waiting on the compressor to recover enough to go back to work. I burnt up a craftsman compressor twice (pump failure) porting and polishing a set of heads. Mind you it was one of the oil-less designs but it still didn't live long running it that hard. I still have it and still use it but I am mindful of how hard I run it and how long.

So basically their motors are not rated for continuous duty. Figure if you put that motor on ANY other piece of machinery, how long and often will it get run? We fire up our lathes and mills and maybe run them for 5 or 10 minutes and then shut them off while we change tools, run in the house to grab something to drink. Walk away to answer a phone. Point is that no other machine in the shop save a fan for air circulation gets run as much as a compressor. And those motors are not up to the task. Buy a Dayton or a Baldor and be done with it. Yes they are expensive, but sometimes you get what you pay for.
 
I read through the listings for the Grizzly motors and couldn't find a reason. Continuous duty motors were and weren't listed for compressor, capacitor start and capacitor start/run- same way and then reversible and non-reversible some were OK and some not OK. Go figure. Might have something to do with inflated HP ratings on some of them. Starting torque might also be a factor.
 
Might have something to do with inflated HP ratings on some of them. Starting torque might also be a factor.


Yeah, I swear they are rating motors now buy power consumption and not shaft RPM and torque.
And the reading they use is with a stalled shaft at startup and it's a measurement of inrush current to boot.
 
I think most compressor rated motors have a service factor rating of 1.25. They also may have a better centrifugal switch than lesser motors due the the expected high cycle rate. Baldor, Dayton, or Leeson would be my choice for a replacement motor.
 
Starting torque is the main problem plus duty cycle. If you're going to run your compressor a lot get the better motors as recommended by others. however if your compressor is only going to be used for occasional short term use, then buy the cheap motor and fit an unloader valve for starting.
 
According to a Leeson book I glanced thru, compressor duty means that it will supply up to 300% at start, of the running torque.
 
the Start capacitors on a compressor duty motor are substantially higher MFD and some also drop out the start winding at a higher RPM.
Both these items require a different start winding. The do deliver substantially higher torque on startup. conventional motors will start a empty compressor but will have trouble with one that is at operating pressure. The only piping that gets relieved by the pressure switch is the inlet pipe to the tank and about 5 strokes of the compressor has it to full pressure so the motor is truly starting under load.

Art B
 
Back
Top