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Discussion Starter · #1 ·
I have a huge air handler/exhaust system for a paint shop. it came with a 3phase 1.5horse / 1750 rpm motor on it. there is no 3phase at this location so we want to change the motor to single phase. is there any calculation to know that whatever size single phase motor can do the same work as the 3 phase motor?

my customer had a 3h /35xx rpm motor that we tried [against my recommendation] and it shortly tripped the breaker as it was pulling twice the amps it should have been.

I found a 2h/1750rpm 240v motor, would that work?
 

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Donuts > Fried Eggs
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Short answer: Yes, your 2HP motor should work fine.
...Is there any calculation to know that whatever size single phase motor can do the same work as the 3 phase motor?
The horsepower rating itself is a measure of that. HP is a direct function of speed and torque.

In your case you want to match the RPMs because your blower is most likely optimized for that speed for a specific amount of airflow. So as long as your motor is nameplate rated for 1750RMP with at least the same amount of HP as the OEM motor, then it doesn't matter what phase/voltage/current it requires.
 

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Discussion Starter · #3 ·
Short answer: Yes, your 2HP motor should work fine. The horsepower rating itself is a measure of that. HP is a direct function of speed and torque.

In your case you want to match the RPMs because your blower is most likely optimized for that speed for a specific amount of airflow. So as long as your motor is nameplate rated for 1750RMP with at least the same amount of HP as the OEM motor, then it doesn't matter what phase/voltage/current it requires.
OK, i was overthinking it. It was the RPM that was screwing it up, which is what I thought, but I didnt want to bring in a motor without knowing that it should work. Thanks!:thumbup:
 

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Discussion Starter · #5 ·
If the 3 hp was correctly sized by the air handler manufacturer, then the 2 hp will not do the job.
initally had a 1.5h 3 phase 1750 rpm
replaced with a 3h, 1 phase 35xx rpm - didnt work right
I want to install 2h, 1 phase 1750 rpm
 

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I was overthinking it too when I first read your posts. The answer big john gave seems so obvious.
 

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Discussion Starter · #7 · (Edited)
I was overthinking it too when I first read your posts. The answer big john gave seems so obvious.
yeah, but id rather confuse myself by thinking too much than be too stupid to not think enough. :laughing:

I errored in thinking phase had to do with output power, but no, HP is HP. just like watts are watts.
 

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initally had a 1.5h 3 phase 1750 rpm
replaced with a 3h, 1 phase 35xx rpm - didnt work right
I want to install 2h, 1 phase 1750 rpm
sorry...I mis read the original motor as being 3hp.
2 hp at the same RPM will be fine.

I think the required horsepower changes with the cube of the change in speed, so your 3500 rpm motor would have to be 9 hp.
 

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Discussion Starter · #10 ·
sorry...I mis read the original motor as being 3hp.
2 hp at the same RPM will be fine.

I think the required horsepower changes with the cube of the change in speed, so your 3500 rpm motor would have to be 9 hp.
Wait, how did you come up with 9 hp?
 

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Electric Al
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Am I missing something ?

Wouldn't you replace a 1.5 HP motor , with a 1.5 HP motor ?
As long as you match the torque and the speed !

Am I wrong ?
 

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Here is another thing to worry about. the 3 phase motor might be required for hazardous location reasons. Class 1 Zone 2 might need an enclosed motor and a single phase motor may have a centrifugal switch which could make it wrong for the location.
 

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Mshea brings up a good point. Make sure the location is not classified and the motor does not have to be Class 1 rated.
 
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