looking for a 3 hp electric Air Compressor motor

[1930artdeco]

Ok. My AC motor is just not powerful enough to turn my rebuilt pump. I am looking for something in the 3 HP range, single phase with a CW (looking at the pulley) rotation. Everything I see is either 1Kish, 3 ph or Home deport quality. Any ideas on where to look for a good quality motor? I am currently trying to use this on a 41 Wayne compressor. There are a few 2 HP but not sure if they have the oompf to turn it. How are the H.F. motors (ick I know)?

Mike

 

[finn]

Industrial Air compressor dealer. Major cities have them. Or any electric supply house as far as that goes.

My local electric shop rebuilds motors or can order whatever I need, and our county population is less than 30000.

There are dozens of compressor houses on the internet that sell quality motors. I found several selling name brand motors last week when looking for a 5hp compressor motor, although the name brands aren’t going to be priced like the no name imports.

Even the name brands are probably going to be imported at the power level you’re looking at, though.

 

[micromind]

Look for used ones. Usually, used is just fine, sometimes you get a dud though.

In my experience, the best brands are Doerr, Leeson (the sons of Lee Doerr), Baldor (the dor part is Lee Doerr's Father), Emerson (which includes many sub-brands) and others I can't think of at the moment.

There are tons of '3HP' motors out there, usually 'compressor duty' that are not 3HP at all. They are labelled 3HP because that's the absolute maximum the motor can produce but only for a short time. A true 3HP single phase motor will draw between 12 and 16 amps @ 230 volts.

Another thing is RPM. A 3450 RPM (or thereabouts) is generally less $$$ but not as good as a 1725 RPM model.

I don't know anything about the HF ones.

 

[larry4406]

Look for used ones. Usually, used is just fine, sometimes you get a dud though.

In my experience, the best brands are Doerr, Leeson (the sons of Lee Doerr), Baldor (the dor part is Lee Doerr's Father), Emerson (which includes many sub-brands) and others I can't think of at the moment.

There are tons of '3HP' motors out there, usually 'compressor duty' that are not 3HP at all. They are labelled 3HP because that's the absolute maximum the motor can produce but only for a short time. A true 3HP single phase motor will draw between 12 and 16 amps @ 230 volts.

Another thing is RPM. A 3450 RPM (or thereabouts) is generally less $$$ but not as good as a 1725 RPM model.

I don't know anything about the HF ones.

Interesting about the lineage of the various motor firms!

 

[johnre]

Century is another reasonable brand. Dayton is a lot more pricey.

Regarding 3450 vs. 1725 RPM, the task here is to match what it is intended to replace for the HP rating, pulley diameter, and RPM. While a 1725 RPM motor will cost more, all else equal, and might be considered "better", it's really the application that matters the most here.

That being said, the pulley diameter can be a variable that you control in order to make either a 1725 or 3450 RPM motor work in an application where new and old are mismatched.

 

[micromind]

Century is another reasonable brand. Dayton is a lot more pricey.

Century is indeed a good brand, they always have been. These days, it's Century/Magnetek though I don't know who bought out who.

Dayton is good too. Many years ago, GE made Dayton motors then Emerson (after they bought out Doerr), these days it's A. O. Smith.

 

[1930artdeco]

So I went to the local shop that rebuilds/sells motors. The one they had on the shelf won’t work for my application. He said that it would burn itself up being only a two pole motor vs. a four pole. Essentially just not enough torque.

He recommended and explained a VFD for a three phase motor. So I am now looking to get a 3 phase 3-5 hp motor. It will be less expensive than a single phase motor of equivalent hp. So I will get a motor have them set it all up and call the electricians back out. And who knows maybe next year I will have a functioning air compressor.

 

[LopezBart]

So I went to the local shop that rebuilds/sells motors. The one they had on the shelf won’t work for my application. He said that it would burn itself up being only a two pole motor vs. a four pole. Essentially just not enough torque.

He recommended and explained a VFD for a three phase motor. So I am now looking to get a 3 phase 3-5 hp motor. It will be less expensive than a single phase motor of equivalent hp. So I will get a motor have them set it all up and call the electricians back out. And who knows maybe next year I will have a functioning air compressor.

The big advantage of the VFD is being able to set a reasonable acceleration ramp; this will greatly reduce inrush current, since you're not applying full power to an essentially locked stator.

 

[PoorUB]

So I went to the local shop that rebuilds/sells motors. The one they had on the shelf won’t work for my application. He said that it would burn itself up being only a two pole motor vs. a four pole. Essentially just not enough torque.

He recommended and explained a VFD for a three phase motor. So I am now looking to get a 3 phase 3-5 hp motor. It will be less expensive than a single phase motor of equivalent hp. So I will get a motor have them set it all up and call the electricians back out. And who knows maybe next year I will have a functioning air compressor.

That will work, but unless you find a used 3PH motor, I doubt is will be much less money. A 1PH in, 3PH out VFD for 3 or 5 HP won't be cheap either.

I bought a compressor with a 5HP, 3PH motor and ran across a used 1PH. I looked into a VFD and decided it was too much money, and I had the motor already! Of course, unless you are looking at some Amazon Chinese no-name VFDs.

 

[1930artdeco]

I found a used 3 ph/5 hp Baldor for $400 and I will check it at the shop and if it works I will grab it as there is nothing around in the single phase category. They will set the VFD for me to match the motor. At this point I just want the damn thing running.......

 

[gimpyrobb]

Shame you're not closer!

 

[1930artdeco]

Well, the baldor motor got sold but he has a 2 HP 3ph Nord motor with a reduction gear. I will take the reduction gear off because I don't need it. So if it is a 4 pole it should work but I will have it tested in a shop.

 

[stonesfan68]

I'd try Zoro. If you can find a 15-20% off coupon they are generally pretty price competitive especially since they offer free shipping.

 

[no704]

Check out Surplus Center. Online.

 

[whateg01]

Well, the baldor motor got sold but he has a 2 HP 3ph Nord motor with a reduction gear. I will take the reduction gear off because I don't need it. So if it is a 4 pole it should work but I will have it tested in a shop.

If you were worried that a 2hp motor wasn't going to work before, why is it ok now?

 

[Shoreline_]

But maybe your driving pulley is too large? A smaller pulley would be cheaper.

 

[1930artdeco]

The guys at the shop said that a 2 pole 1.5 hp won't last (it tripped the breaker after 30 sec. of run time). A 4 pole hopefully is a little beefier torque wise and will last. I will ask on Monday and if they say no then I will look again for another one....I am not smart when it comes to electric motors, I am hoping 3 ph is a bit more powerful than single ph.

 

[micromind]

The guys at the shop said that a 2 pole 1.5 hp won't last (it tripped the breaker after 30 sec. of run time). A 4 pole hopefully is a little beefier torque wise and will last. I will ask on Monday and if they say no then I will look again for another one....I am not smart when it comes to electric motors, I am hoping 3 ph is a bit more powerful than single ph.

Typically, a 3Ø motor with 3Ø utility power will have more starting torque than a single phase one but with a VFD it'll have less.

 

[1930artdeco]

Oh, ok didn’t know that. Well….rats.

 

[u3b3rg33k]

Typically, a 3Ø motor with 3Ø utility power will have more starting torque than a single phase one but with a VFD it'll have less.

Oh, ok didn’t know that. Well….rats.

with a properly spec'd "name brand" VFD you'll have 150-200% of running torque for startup with a VFD. either way you need an unloader if you want things to work properly.

 

[N_Jay]

Have you tried here

https://surpluscenter.com/electrical/

 

[N_Jay]

with a properly spec'd "name brand" VFD you'll have 150-200% of running torque for startup with a VFD. either way you need an unloader if you want things to work properly.

A good VFD with a soft start feature will have more torque during start up.

 

[whateg01]

The guys at the shop said that a 2 pole 1.5 hp won't last (it tripped the breaker after 30 sec. of run time). A 4 pole hopefully is a little beefier torque wise and will last. I will ask on Monday and if they say no then I will look again for another one....I am not smart when it comes to electric motors, I am hoping 3 ph is a bit more powerful than single ph.

Yes a 4 pole motor has more torque, roughly twice what a 2 pole has. It also spins half the speed so to get the speed back you have to have pulley sizes adjusted. Doing so cuts the torque in half so you're right back where you started. You need to know how fast you want to spin the pump. Then size the motor accordingly.

 

[u3b3rg33k]

A good VFD with a soft start feature will have more torque during start up.

these are the ratings I'm referring to.


the only time i've seen a VFD compressor fail to start was when the unloader wasn't operating properly. I've seen big boy DOL compressors start fully loaded. wish I'd thought to throw an amp-clamp set for inrush on that!

 

[Sumboodie]

Look for used ones. Usually, used is just fine, sometimes you get a dud though.

In my experience, the best brands are Doerr, Leeson (the sons of Lee Doerr), Baldor (the dor part is Lee Doerr's Father), Emerson (which includes many sub-brands) and others I can't think of at the moment.

There are tons of '3HP' motors out there, usually 'compressor duty' that are not 3HP at all. They are labelled 3HP because that's the absolute maximum the motor can produce but only for a short time. A true 3HP single phase motor will draw between 12 and 16 amps @ 230 volts.

Another thing is RPM. A 3450 RPM (or thereabouts) is generally less $$$ but not as good as a 1725 RPM model.

I don't know anything about the HF ones.

That's cool info on Baldor, Lesson and Doer

 

[Sumboodie]

Shane you aren't near. I have a 3 phase 5hp I'd give you. It's of no use to me.

 

[Shoreline_]

4 pole motor is half the speed. Power being equal, you can get the same torque from a 2 pole motor with a pulley half the size.

 

[1930artdeco]

Well the 3 HP ran more than 30 sec. and didn't blow the breaker! Next up is to keep the intercooler lines from grinding on the flywheel and then I will let her fill the tank.

 

[finn]

I don’t see where a 30 second run will tell you much of value. Horsepower requirements are proportional to pump load, ie the tank pressure the pump is working against. At 30 seconds your tank is no where near the cutoff pressure, so there isn’t really much motor horsepower draw.

 

[whateg01]

I don’t see where a 30 second run will tell you much of value. Horsepower requirements atr proportional to pum load, ie the tank pressure the pump is working against. At 30 seconds your tank is no where near the cutoff pressure, so there isn’t really much motor horsepower draw.

I wish more people understood this. Or, more broadly, a motor doesn't "put out" HP. A load draws that from the motor and the motor is able to provide what the load requires or it isn't. If the load only needs 1/4 HP, that's all the motor is producing.

 

[finn]

I wish more people understood this. Or, more broadly, a motor doesn't "put out" HP. A load draws that from the motor and the motor is able to provide what the load requires or it isn't. If the load only needs 1/4 HP, that's all the motor is producing.

Science in general isn’t well understood by the populace.

These are things that are taught in ninth grade, I would think. Instead I keep hearing how we need more wood shop classes.

It’s sort of frustrating sometimes.

 

[1930artdeco]

You are correct. I was basing my happiness of more than 30 sec. On the previous motor. It would run for 30 sec and trip the breaker. So next weekend I will do a full test run.