# How am I to know everything.



## McClary’s Electrical (Feb 21, 2009)

Yes, you replace with a 10 hp, and reduce the pulley size by 1/3. Inform him (obviously) that this will double the pump up time for this compressor.


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## 51360 (Jun 9, 2014)

robocop said:


> A customer has a 15hp 3ph 230/460 254t frame motor for a compressor. But he does not have a 3ph service available. Looked at many options and *he just wants to put a 10hp 1ph 230v motor in its place(least expensive option) *I don't know the first thing about pulleys and how to deal with shaft sizes and the different heights of the shaft, let alone know if a 10hp will turn over the compressor, how is one to figure all this out?


Just curious, who decided to use this motor as a replacement?

Edit: didn't see mcclary's response.

Borgi


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## robocop (Jan 29, 2015)

The owner asked for it, he said he will
Just loose out on some cfm. But he's not think about everything else involved with a smaller motor. And biggest size in 1ph I can find is 10hp.


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## robocop (Jan 29, 2015)

Is there not some trade that deals with pulleys and design of things like that? How do you know to reduce pulley to 1/3 the size? How do you know it will even turn over the compressor pistons?


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## drewsserviceco (Aug 1, 2014)

Millwrights are the trade that deals with this stuff. Generally they are lifting and setting motors or equipment measured in tons with tolerances to the thousandth of an inch. 

However, there are formulas available as far as determining rpm and torque changes between pulley diameters.


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## 51360 (Jun 9, 2014)

robocop said:


> The owner asked for it, he said he will
> Just loose out on some cfm. But he's not think about everything else involved with a smaller motor. And biggest size in 1ph I can find is 10hp.


Thanks, important info. 

Obviously a wise decision, obviously someone had a plan. :thumbsup:

Borgi


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## shocksystems (Apr 25, 2009)

Can you get input from the manufacturer in this case?

Cheers!

Jim


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## McClary’s Electrical (Feb 21, 2009)

robocop said:


> Is there not some trade that deals with pulleys and design of things like that? How do you know to reduce pulley to 1/3 the size? How do you know it will even turn over the compressor pistons?


A hp is 745 watts. A hp is a hp, is a hp. The owner asked for a 10 because that's generally the largest single phase motor available. It's 1/3 less hp, so you need to reduce pulley size by 1/3


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## hardworkingstiff (Jan 22, 2007)

I would think this would be a perfect use of a rotary phase converter.


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## glen1971 (Oct 10, 2012)

hardworkingstiff said:


> I would think this would be a perfect use of a rotary phase converter.


Or a VFD...


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## JRaef (Mar 23, 2009)

glen1971 said:


> hardworkingstiff said:
> 
> 
> > I would think this would be a perfect use of a rotary phase converter.
> ...


That would work, but the cure might be more expensive than the compromise. It would need at LEAST a 30HP VFD, then the conductors feeding the VFD would need to be 125% of the VFD amp rating, not the motor. So you are looking at sizing the conductors at over 100A from the breaker panel to the VFD. That ain't chicken feed. (No offense Chicken Steve)

You can get 15HP 230V single phase motors, but call a real motor shop, don't expect it to be on a web site reseller, they cherry pick the high volume movers.

I would get a Baldor L3912T, it's a 208-230V rated version, which may come in handy of he ever moves. 254T frame. Should drop right in.


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## John Valdes (May 17, 2007)

I see no mention of RPM?
How could you replace a motor and not concern yourself with producing the needed torque required to turn the motor?

I would do a torque calculation, then choose my motor!
Never size any motor to HP. You can get in trouble if you do. Big trouble.


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## JRaef (Mar 23, 2009)

John Valdes said:


> I see no mention of RPM?
> How could you replace a motor and not concern yourself with producing the needed torque required to turn the motor?
> 
> I would do a torque calculation, then choose my motor!
> Never size any motor to HP. You can get in trouble if you do. Big trouble.


Excellent point, my bad. I also screwed up, that motor is a 256T frame, the old one is a 254T. Baldor has a 254T frame version as well, the L1177T, but it is only available in 1760RPM. There are others out there that do have 3450RMP in that frame size, they are just brands I haven't heard of. My real point though was that he should be working with a real motor shop, they wouldn't have made my mistake(s).


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## robocop (Jan 29, 2015)

Thx for all the comments!! The rpm is the same at 1740, and good news the max rpm on the pistons of the compressor is 900rpm so with a proper sized pulley it's gonna run great. And good point with the torque I compared it and there's 20lb ft difference. Between 10hp and 15hp


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## John Valdes (May 17, 2007)

robocop said:


> Thx for all the comments!! The rpm is the same at 1740, and good news the max rpm on the pistons of the compressor is 900rpm so with a proper sized pulley it's gonna run great. And good point with the torque I compared it and there's 20lb ft difference. Between 10hp and 15hp


I once sized a motor and drive for a horizontal lathe (12') diameter for a DC to AC conversion.
I replaced a 900 rpm motor with a 1800 rpm motor and increased the hp.
Big mistake and lucky for me, the lathe was built many years ago and the motor was over kill for the application.

I still has serious issues with ramping down and faulting on over voltage dc buss (OV).
I was able to get it to work after resizing the pulleys and adding a resistor bank to the drive.
I will never forget as I lost a few nights of sleep over this.


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## McClary’s Electrical (Feb 21, 2009)

robocop said:


> Thx for all the comments!! The rpm is the same at 1740, and good news the max rpm on the pistons of the compressor is 900rpm so with a proper sized pulley it's gonna run great. And good point with the torque I compared it and there's 20lb ft difference. Between 10hp and 15hp


You're adding torque by reducing that drive pulley


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## Bootss (Dec 30, 2011)

Sell the customer two single phase compressors, and then they can rotate in the time online for ea. compressor.


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