variable speed motor and controler

[rockedawg]

I am trying to set up a couple of warehouse size fans, 1 mounted high and one at ground level. I would like to find variable speed single phase motors and controls for each of these fans, the one mounted high will need at least 1/2 hp. 1725 rpm , although i would not mind having 3/4 hp, 1725 rpm. i am thinking 1.5 hp 1725 rpm on the larger ground level . can anyone give me some information on where to look for this type set up . would love to have infinitely variable speed, without burning up the motor. thanks for any help offered

 

[jraef]

Very difficult to do at that HP with 1 phase motors. Easier to use 3 phase motors and get a VFD that will convert your 1 phase source to 3 phase going to the motor. At that HP level you will not need to even derate the VFDs.

JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> faq731-376

 

[itsmoked]

And the motors may be smaller and less expensive. If you are going to build these from scratch, make sure you get the fan blades first and then get the correct motors to match. I just had a friend go thru the opposite method with a lot of pain. Seems fans available in less choices then motors.



Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[rockedawg]

got the fans, one 36" blade up top, and one 56" on bottom, the one up top had 1/2 hp on it, the one on bottom had no motor so i was using similar fans as a refernce to come up with the 1.5 hp motor size for it . so if i were to use a rotary phase converter i assume, and use 3 phase motors on these fans. would that be wasting or using more electricity than running a single speed single phase motor in the same application ?

 

[jraef]

A rotary phase converter will waste energy. Don't do it that way.

What I was suggesting was a Variable Frequency Drive, an electronic speed controller for 3 phase motors. Even if you had no need of variable speed, one of their side benefits is their ability to convert 1 phase power to 3 phase for a motor (not for other uses). They just use incoming line power as a "raw material", converting it to DC. Then they use the DC to do what is called "inversion" which is to create a new 3 phase AC output. That output can be of variable voltage and frequency so that an AC motor can change speed without losing torque or overheating. that method of speed control is in fact infinitely variable. The only remaining issue is that you cannot run AC motor too slowly without risking overheating because their internal cooling fans also slow down. That usually isn't an issue with paddle fans however because at too low of a speed they quit moving much air themselves anyway, so the motor load drops off exponentially.

They do make VFDs for specific types of 1 phase motors, namely PSC (Permanent Split capacitor) or Shaded Pole. Not only can you not apply them to any other type of 1 phase motor, but but as Keith said, the 1 phase motors will be bigger, less efficient, more expensive and more prone to failure. Plus the VFDs for 1 phase motors are very expensive compared to those for 3 phase motors.

JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> faq731-376