Tell me about electrical motors

Investigator

Investigator

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I need a 5hp electrical motor for a air compressor I'm building from scratch. Since I'm starting from zero, I can use any frame size, any rpm etc. What I'm trying to learn is what motor I should look for. I need a true 5hp, so I'm looking at amp draw of 20-23amps. But after that, does it matter what frame size it is? or what RPM? Ideally I would love to find nice, free Baldor 5hp at about 1750rpm in a 184 frame size. But those look to start at about $700 and go up quickly. I have seen motors on 'bay that are 56 frame size, pulling 21 amps at 3450rpm at about $275. Would that do just as well?

What do I not know?
 
Investigator said:
I need a 5hp electrical motor for a air compressor I'm building from scratch. Since I'm starting from zero, I can use any frame size, any rpm etc. What I'm trying to learn is what motor I should look for. I need a true 5hp, so I'm looking at amp draw of 20-23amps. But after that, does it matter what frame size it is? or what RPM? Ideally I would love to find nice, free Baldor 5hp at about 1750rpm in a 184 frame size. But those look to start at about $700 and go up quickly. I have seen motors on 'bay that are 56 frame size, pulling 21 amps at 3450rpm at about $275. Would that do just as well?

What do I not know?
Click to expand...
The RPM isn't such a big deal, your drive pulleys will set the RPM of the compressor head. The real issue is the service rating, you want one that is ratted for compressor service, there is a difference.
 
verbotenwhisky said:
The RPM isn't such a big deal, your drive pulleys will set the RPM of the compressor head. The real issue is the service rating, you want one that is ratted for compressor service, there is a difference.
Click to expand...
is that the service factor (SF) on the tag? what should it be?
 
"Service Duty" Continuous (cont)
I don't remember a 56 frame that is 5 hp but that is irrelevant.
I would prefer the 1750 rpm over the 3450 they are generally more poles smoother and more torque.
 
You need to look at the compressor specs to determine the speed required for the motor Hp and then work out the pulley ratios for the motor speed. A 1750 RPM is typically used for more heavy duty compressors, and also a higher service factor. A 1750 RPM motor should be a bit quieter than a 3450 RPM, but the noise from the compressor will be the dominating factor. The 1750 RPM motors tend to be used on lower speed compressors something like 600-1200 RPM, mine is ~800 RPM for 5Hp. I have a Champion 5Hp industrial type of compressor, they switched to WEG motors when I bought it a number of years ago, they were having reliability issues with the Baldor motors that were being made in Mexico. The WEG motor listed below is all cast iron and has a service factor of 1.25.

Zoro lists the the 5Hp WEG at $521, and I routinely get 15-20% discounts if you sign up for their emails. It also includes free shipping, given that the motor is 95 lbs. would be very costly to ship otherwise. Price with 20% discount works out to around $416.
www.zoro.com

Weg Air Compr Mtr, 5 HP, 1745rpm, 208-230V, 184T 00518OS1CCD184T | Zoro

Order Weg Air Compr Mtr, 5 HP, 1745rpm, 208-230V, 184T, 00518OS1CCD184T at Zoro.com. Great prices & free shipping on orders over $50 when you sign in or sign up for an account.
www.zoro.com www.zoro.com
 
mksj said:
You need to look at the compressor specs to determine the speed required for the motor Hp and then work out the pulley ratios for the motor speed. A 1750 RPM is typically used for more heavy duty compressors, and also a higher service factor. A 1750 RPM motor should be a bit quieter than a 3450 RPM, but the noise from the compressor will be the dominating factor. The 1750 RPM motors tend to be used on lower speed compressors something like 600-1200 RPM, mine is ~800 RPM for 5Hp. I have a Champion 5Hp industrial type of compressor, they switched to WEG motors when I bought it a number of years ago, they were having reliability issues with the Baldor motors that were being made in Mexico. The WEG motor listed below is all cast iron and has a service factor of 1.25.

Zoro lists the the 5Hp WEG at $521, and I routinely get 15-20% discounts if you sign up for their emails. It also includes free shipping, given that the motor is 95 lbs. would be very costly to ship otherwise. Price with 20% discount works out to around $416.
www.zoro.com

Weg Air Compr Mtr, 5 HP, 1745rpm, 208-230V, 184T 00518OS1CCD184T | Zoro

Order Weg Air Compr Mtr, 5 HP, 1745rpm, 208-230V, 184T, 00518OS1CCD184T at Zoro.com. Great prices & free shipping on orders over $50 when you sign in or sign up for an account.
www.zoro.com www.zoro.com
Click to expand...
Hummmm looked at mine to see the RPM, doesn't list it on the tag, just says 7.5HP Kaeser.....
 
In your shoes, I'd call Baldor. I've done so previously and they were exceptionally helpful. They sell nothing direct, so there's little to no pressure to buy (though obviously they'll only help you spec a Baldor motor). I called, got the tech info I needed, and a model number, and the rep set up a pick up for me at a local distributor. It was perhaps 20% more than a junk brand - and I got a Baldor! I've been a fan ever since.

GsT
 
Wondering how this might work:
www.ebay.com

5HP Air Compressor Electric Motor 3450RPM Single Phase 7/8" Shaft Heavy Duty | eBay

Air Compressor 5 HP 3450RPM 1 Phase Electric Duty Motor 7/8" Shaft Motor USA Attention: Not all 5 hp motors are exactly the same. So, with the new motor you're purchasing, it's vitally important that you match up the specs on your old motor. All of the information you need to know can be found...
www.ebay.com
 
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