Electric motor question...........

[reman]

I am building a very large whole shop fan in my playhouse. I do want to control the speed, so I am wondering if I can install a rheostat on an older single speed 4 hp air compressor motor. I am thinking probably not but who appreciate any thoughts from those who are much more knowledgable than me. I know I can control the speed with pulleys, but I need to be able to vary the speed easily. Thanks

 

[slow]

Best option is to get a 3 phase motor and a variable frequency controller. Exactly what your asking to do and you get energy savings as a side benefit when lowering the speed.

 

[GMCGarage]

I am building a very large whole shop fan in my playhouse. I do want to control the speed, so I am wondering if I can install a rheostat on an older single speed 4 hp air compressor motor. I am thinking probably not but who appreciate any thoughts from those who are much more knowledgable than me. I know I can control the speed with pulleys, but I need to be able to vary the speed easily. Thanks

You need a VFD to control it without frying your motor, unless you can convert to a DC motor.

 

[rlitman]

Probably not. I have never seen a 4hp compressor with a brushed motor where this would work.

If you have a 3-phase motor, you could do what you want with a VFD.

edit: looks like I took too long to type this, as I was beaten to the post.

 

[James-W]

Best option is to get a 3 phase motor and a variable frequency controller. Exactly what your asking to do and you get energy savings as a side benefit when lowering the speed.

I agree that what you describe would work just fine. But wouldn't it be less expensive to just buy a fan already setup to run at different speeds?

 

[slow]

all depends on the size of the fan. The last one I installed was a 7.5 hp 45,000 cfm fan, so it was great to be able to run it as a 15,000 cfm fan at a much lower speed, and crank up the speed when we needed more airflow (but it was much louder at full speed)

 

[reman]

Thanks for the responses so far. Good info. I saw this on fleabay and wondered how it might work in my application.

https://www.ebay.com/itm/For-Router...aEAAOSwyW5a7fKS:sc:USPSFirstClass!32421!US!-1

 

[reman]

I agree that what you describe would work just fine. But wouldn't it be less expensive to just buy a fan already setup to run at different speeds?

d



You are probably right if I were buying all the parts. But the fact is that I have all these pieces on hand except for the variable speed issue. I could hook it up as a single speed with what I have. Plus I have Lotsa time and little $$. lol As well as trying to use up some of the **** I have accumulated over a lifetime.

 

[dogdog]

Thanks for the responses so far. Good info. I saw this on fleabay and wondered how it might work in my application.

https://www.ebay.com/itm/For-Router...aEAAOSwyW5a7fKS:sc:USPSFirstClass!32421!US!-1

It would not work well on a true AC motor (induction type)... does work on motors with a carbon brush type though...but weaker unless at full speed... I used that on the grinder and routers, but they are Brushed AC motors... Not sure about energy consumption.... and also Not sure about 4HP motor 15AMPx120V = about 1800 Watt... 4HP is about 2982.8 Watt and that is not even including that initial current draw of the motor. ... most whole house fan motor I seen are 1/2 HP...

 

[Davefr]

I am building a very large whole shop fan in my playhouse. I do want to control the speed, so I am wondering if I can install a rheostat on an older single speed 4 hp air compressor motor. I am thinking probably not but who appreciate any thoughts from those who are much more knowledgable than me. I know I can control the speed with pulleys, but I need to be able to vary the speed easily. Thanks

Reostats won't work with split phase induction motors. Why don't you get a HVAC air handler motor that uses winding taps to control speed. Use a rotary switch to select the speed.

 

[Mooky]

Check your motor specs for full load current. Also your fan curves to determine the horsepower required.

This company has a series of single phase speed controllers, 230 volt version linked:. https://www.kb-controls.com/product.sc?productId=140&categoryId=25

 

[redmondjp]

Reostats won't work with split phase induction motors. Why don't you get a HVAC air handler motor that uses winding taps to control speed. Use a rotary switch to select the speed.

That's exactly what I was going to suggest. Go to your nearest HVAC contractor and see if he has any old outdoor cooling unit fans which you could obtain either free or cheap. Make sure you get the motor capacitor as well - on some of those units the capacitor is mounted remote from the motor itself.

 

[reman]

Reostats won't work with split phase induction motors. Why don't you get a HVAC air handler motor that uses winding taps to control speed. Use a rotary switch to select the speed.

I think that is probably to most practical way to achieve my desired result. I had not really considered it because of the low hp motors. My fan is a regular bladed fan, with 3blades and about 3 feet diameter. Would the small HVAC motor pull this? I am sure there is a required torque difference, from what a squirrel cage or smaller blade requires. Thoughts?