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Variable Speed Fan Question


 
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Kerwin
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PostPosted: Thu Feb 28, 2013 9:47 am    Post subject: Variable Speed Fan Question Reply to specific post Reply with quote

Does anyone know if it is possible to vary the speed of a wall ventilation fan? Found a wall vent fan that I'd like to use for a poultry shed, where variable speed would be ideal. 20 inch fan with a 1/3 HP motor. It appears to be single speed as setup, but wondering if a variable switch could be possible.
 
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JMOR
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PostPosted: Thu Feb 28, 2013 9:53 am    Post subject: Re: Variable Speed Fan Question Reply to specific post Reply with quote

Kerwin wrote:
(quoted from post at 13:47:26 02/28/13) Does anyone know if it is possible to vary the speed of a wall ventilation fan? Found a wall vent fan that I'd like to use for a poultry shed, where variable speed would be ideal. 20 inch fan with a 1/3 HP motor. It appears to be single speed as setup, but wondering if a variable switch could be possible.
It depends on motor type. 1/3 is a bit on the large size for a universal motor, which can be slowed, but could be one that size, but unlikely. Some other type can be slowed, but others will simply burn up when operated on low voltage. How is it started? Centrifugal switch, capacitor, ?,?,? Answer is probably not.
 
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David G
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PostPosted: Thu Feb 28, 2013 9:55 am    Post subject: Re: Variable Speed Fan Question Reply to specific post Reply with quote

A VFD would be a good application for that.
 
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Dean
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PostPosted: Thu Feb 28, 2013 10:19 am    Post subject: Re: Variable Speed Fan Question Reply to specific post Reply with quote

The fan is no doubt driven by an induction motor.

You must use a VFD to operate an induction motor at variable speed.

Dean
 
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JMOR
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PostPosted: Thu Feb 28, 2013 10:22 am    Post subject: Re: Variable Speed Fan Question Reply to specific post Reply with quote

David G wrote:
(quoted from post at 13:55:28 02/28/13) A VFD would be a good application for that.
OK, a question for you. Induction motor with a start winding switched out once it comes up to speed. You feed it with the VFD and set speed low enough the the start winding is still switched in by the centrifugal switch. How will this motor do in this situation? I'm reasonably sure that smoke is in the answer.
 
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David G
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PostPosted: Thu Feb 28, 2013 10:27 am    Post subject: Re: Variable Speed Fan Question Reply to specific post Reply with quote

Just hook the VFD to the motor, it will take care of providing current and voltage to start it. It varies the frequency, voltage and current.
 
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David G
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PostPosted: Thu Feb 28, 2013 10:29 am    Post subject: Re: Variable Speed Fan Question Reply to specific post Reply with quote

In response to the start windings, will have to check. I believe you take the start windings out of the circuit.
 
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JMOR
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PostPosted: Thu Feb 28, 2013 10:56 am    Post subject: Re: Variable Speed Fan Question Reply to specific post Reply with quote

David G wrote:
(quoted from post at 14:29:10 02/28/13) In response to the start windings, will have to check. I believe you take the start windings out of the circuit.
Unless I'm badly mistaken, I do not believe you can start a single phase motor with one winding.
 
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David G
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PostPosted: Thu Feb 28, 2013 11:06 am    Post subject: Re: Variable Speed Fan Question Reply to specific post Reply with quote

I have an email into Allen Bradley on how to do that, will post when I get a result.
 
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David G
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PostPosted: Thu Feb 28, 2013 11:16 am    Post subject: Re: Variable Speed Fan Question Reply to specific post Reply with quote

We have stumped the district engineer, it is headed for Milwaukee now.
 
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Bill in IL
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PostPosted: Thu Feb 28, 2013 11:43 am    Post subject: Re: Variable Speed Fan Question Reply to specific post Reply with quote

My guess without knowing what type of motor you have on the fan is no it cannot be speed regulated.

You need to have a 3 phase motor to use the VFD. Therefore no start circuit in the motor just 3 windings one for each phase to create the "rotating" magnetic field. The VFD would create a variable frequency output to control they syncronous speed of the motor.

What about repowering it with a motor for a furnace blower? Many of those are multi speed.
 
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David G
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PostPosted: Thu Feb 28, 2013 11:45 am    Post subject: Re: Variable Speed Fan Question Reply to specific post Reply with quote

I am going to stand corrected, it is not practical to use a VFD on a single phase motor with a capacitor start. The VFD does not like seeing the capacitors during starting.
 
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Tramway Guy
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PostPosted: Thu Feb 28, 2013 2:22 pm    Post subject: Re: Variable Speed Fan Question Reply to specific post Reply with quote

Use a three-phase motor, using a VFD...the VFD will run on single phase in. Just have to size the VFD a little larger than normal for the size of motor.
 
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Bob
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PostPosted: Fri Mar 01, 2013 10:03 am    Post subject: Re: Variable Speed Fan Question Reply to specific post Reply with quote

NO need to attempt to "re-invent the wheel" and mix and match your own fan and speed controller.There ALL SORTS of choices for variable speed or thermostatically speed controlled vent fans for livestock buildings. Local hog confinement barns near here have them as well as a friend"s turkey barns, for example. Don"t know the brand names, offhand, but GOOGLING "Variable speed confinement building fan" will get you started.


There's some educational resource links at the end of the .pdf linked below.

http://learningstore.uwex.edu/Assets/pdfs/A3784-06.pdf

MORE info:

http://www.munters.com/upload/Related%20product%20files/controls-5000seriesliterature.pdf
 


Last edited by Bob on Fri Mar 01, 2013 10:07 am; edited 3 times in total
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missouri massey man
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PostPosted: Fri Mar 01, 2013 11:58 am    Post subject: Re: Variable Speed Fan Question Reply to specific post Reply with quote

Kerwin wrote:
(quoted from post at 10:47:26 02/28/13) Does anyone know if it is possible to vary the speed of a wall ventilation fan? Found a wall vent fan that I'd like to use for a poultry shed, where variable speed would be ideal. 20 inch fan with a 1/3 HP motor. It appears to be single speed as setup, but wondering if a variable switch could be possible.


Does the "mushroom" fan you are planning on using have a gray metal oval capacitor (or gray plastic oval) attached to the side of the motor? Or is it a belt drive motor with the same style capacitor?? If so, these motor will be what is called a "Permanent Split Capacitor" (PSC) motor and can be varied in speed with nothing more that a wall mount rheostat or speed controller. Check WWGrainger to locate. These motors do not have a centrifugal switch nor do they have a start winding that is required to be removed from the circuit. The gray oval "run" capacitor stays in the circuit continuously and limits the amount of current through the start winding after start-up.

The fact that a capacitor is on the motor reflects that it is a single phase motor, but if it were in fact a three phase motor, it could be run safely on single phase by powering it with a vfd and will allow it to operate at infinite rpm from 0 to the maximum rpm rating of the motor.

If it has a black plastic (bakelite) round (tubular) capacitor, that would indicate a "capacitor start" motor and would have a centrifugal switch internally. These types of Greenheck, Carnes, etc aluminum mushroom ventilators when set up for single phase have the PSC motors, whether belt drive or direct drive.

Hopefully this is helpful info, not too boring and not too long of a reply......
 
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