7.5 hp motor and compressor?

I need a new compressor, also a motor. Figured I would get the motor first. I am looking at a 32 cfm displacement pump from eaton, go big or go home. I have been looking around ebay at 7.5 hp motors but the thing that worries me is the power source, i see some of them require 3 phase, and other just don't have any details. Right now i have a 3 hp motor and it just runs off 220 plugged into a wall outlet that looks like a big version of a regular 110 wall socket. In the breaker box its 110 sources are on one of those dual 50 amp breakers.

Anyway the pump i am looking at just says it runs at 840 rpm, so thats a number to work with. They also have another 32 cfm pump that has the same RPM and on the site it says "For an 840 RPM speed, you should use a TRUE 7.5 HP, 32-amp, 215-T Frame, 1750 RPM motor." So i have a feeling that the same numbers apply to the one I am looking at, the onyl reason i am not looking at that pump is because it has "head unloaders" to make it easier to start with a gasoline engine. Unless that is no big deal? Its in stock the other one isnt.

So what I get is that I need
-7.5 hp
-32 amp
-215-T frame ??????
-1750 RPM

Will a motor of this nature be able to run off of my existing plug?
What is 215-t frame?
32 amp, is that divided between both 110 lines? like 16 amps per wire?

If 7.5 hp is a bad idea maybe I should be looking into 5 hp models.

I am planing on checking a shop first that has rebuilt motors for me before to see if they have anything in the back for sale, they had a lot of motors back when I was getting my 3 hp one rebuilt. If they have a 7.5 hp one I would probably buy it since shipping a motor on e-bay is like 250 dollars. But need some numbers to work with. Hope i have written out my concerns in a legible fashion

I bought my single phase 1750 rpm 7.5HP Baldor from weco_group on Ebay, great price and service. It is powering an Eaton compressor. Don't forget you will need a starter for a motor of this size.

http://shop.ebay.com/merchant/weco-group_W0QQ_dmdZ1QQ_ipgZ50QQ_sopZ12

I actually found a baldor motor on e-bay that the freight shipping was 120 but close enough for i could use 40 dollars worth of gas and just go pick up. but its a 1770 rpm 213TC frame and i have no idea what frame means.

Frame models have to do with the size of the mounting base, spread of the holes, the offset of the base to the end of the motor, the actual frame of the motor (open, closed, or some variation of).

A 32 amp motor will probably need a 50 amp breaker to allow it to start up without tripping. I have a 7.5 hp that is also (IIRC) 32 amp and I operate it on a 50 amp breaker. Never tried 40, figured it would not start. I am using #6 wire, but you could run this with #8 and stay legal.

As others have noted, you will also need a magnetic starter ($$$) and unless the compressor is within 50ft of, and in sight of, the breaker, it will need a disconnect at the compressor.

Charles

First consider 1 phase or 3 phase. If you don't have 3 phase coming into your property (and unless it is commerial or industrial you probably don't and even not all commercial property has 3 phase) you must stay 1 phase.

Second consider amp draw and wire size. The 50 amp breaker is sufficent to run a 32 amp motor. Now the question is, is the wire from the breaker to the plug heavy enough. I would want at least 8 guage wire, 6 guage if it is a long run (50 ft or more).

Third, 215-T frame is an industry standard designation for many dimensions on the motor. The mounting holes will be standard on all 215-T motors as well as shaft size.

Amps divided between 2 lines? No, each line will carry 32 amps as the current alternates direction 60 times a second. AC equals Alternating current 60 hertz ( 60 times a second)

Horsepower required? 5 0r 7.5 Size the motor according to the specs of the pump you are buying

RPM The motor rpm is probably not critical because you can size the pulleys for correct rpm of the pump and pump supplier can certainly size the pulleys for you. There may be a reason they suggest 1750 rpm though.

Hope this helps.

Oh that motor is 3 phase so i can't get that. It looked like 12 ga wire but i can change it easy it is only abut 15 feet away. This info is helping so far. I will check tomorrow for a local motor. I don't like the price tag on the weco-group motors

You never did say, what are you mounting this pump and motor on? and don't forget the pressure switch and magnetic starter.

If you don't already have an 80 gal tank rated to 200 psi with a mounting plate that will handle the pump and motor, you probably will be better off buying a whole new compressor. If your compressor has a much smaller motor and pump, the mounting base will not be anywhere near large enough. 7.5 hp motors are HUGE, and so are pumps of that size. Someone else on here posted a pic of what they had to do when they adapted some large stuff to an mounting intended for a smaller pump/motor, and they had to weld on additional plate and supports.

Charles

"I don't like the price tag on the weco-group motors "

Then you are not familiar with the price of quality new single phase motors in 7.5 hp.

"RPM The motor rpm is probably not critical because you can size the pulleys for correct rpm of the pump and pump supplier can certainly size the pulleys for you. There may be a reason they suggest 1750 rpm though."

They spec 1750 RPM because the pulleys they supply are sized to obtain 850 rpm from a 1750 rpm motor, any variation will raise the cost of the pump.

Satatic said:

Anyway the pump i am looking at just says it runs at 840 rpm, so thats a number to work with. They also have another 32 cfm pump that has the same RPM and on the site it says "For an 840 RPM speed, you should use a TRUE 7.5 HP, 32-amp, 215-T Frame, 1750 RPM motor." So i have a feeling that the same numbers apply to the one I am looking at, the onyl reason i am not looking at that pump is because it has "head unloaders" to make it easier to start with a gasoline engine. Unless that is no big deal? Its in stock the other one isnt.

Click to expand...

Head unloaders aren't just for gas engines.

LoneGunman said:

I bought my single phase 1750 rpm 7.5HP Baldor from weco_group on Ebay, great price and service. It is powering an Eaton compressor. Don't forget you will need a starter for a motor of this size.

http://shop.ebay.com/merchant/weco-group_W0QQ_dmdZ1QQ_ipgZ50QQ_sopZ12

Click to expand...

x2

Satatic said:

Oh that motor is 3 phase so i can't get that. It looked like 12 ga wire but i can change it easy it is only abut 15 feet away. This info is helping so far. I will check tomorrow for a local motor. I don't like the price tag on the weco-group motors

Click to expand...

Good luck, I searched for months to find a motor that beat their prices. Yeah, you can buy a **** one for cheaper, good luck finding a cheaper Baldor.

My tank should hold it its 120 gallon I think its at least 1/4 inch thick and the inside is ceramic coated to prevent rust. Looks like everything is 3 phase anyway. I will look locally first i know they have motors at the farm store.

I love my head unloaders, no gas engine here.

"My tank should hold it its 120 gallon "

Should hold? you have bigger balls than me. There's no tag on the tank that lists the maximum working pressure?

"7.5 hp motors are HUGE, and so are pumps of that size. Someone else on here posted a pic of what they had to do when they adapted some large stuff to an mounting intended for a smaller pump/motor, and they had to weld on additional plate and supports."

Yup, me and someone else posted pics, I had to add over a foot to fit the motor and the pump.

Satatic said:

My tank should hold it its 120 gallon I think its at least 1/4 inch thick and the inside is ceramic coated to prevent rust.

Click to expand...

Should hold? as in "It should be able to hold the pressure"? is that what you mean by that statement?

If there's no tag on it with a certification as a pressure vessel, don't even think about using it as a pressure tank, it doesn't matter how thick it is.

If it was designed as a pressure tank, it will say so. If it wasn't designed as a pressure tank, it may not be safe as one. you're playing with fire. Do you have any idea how much energy is stored in a 120 gallon tank at over 100 psi? can you say darwin awards?

mike944 said:

Should hold? as in "It should be able to hold the pressure"? is that what you mean by that statement?

If there's no tag on it with a certification as a pressure vessel, don't even think about using it as a pressure tank, it doesn't matter how thick it is.

If it was designed as a pressure tank, it will say so. If it wasn't designed as a pressure tank, it may not be safe as one. you're playing with fire. Do you have any idea how much energy is stored in a 120 gallon tank at over 100 psi? can you say darwin awards?

Click to expand...

Its an AO Smith boiler tank built beyond specs. It will hold.

I think I may end up having to go with a 5 hp motor. Seems to be half the price and 1/8 the shipping.