Help on Motor Speed Controls

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scottdbutcher

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Hey Guys,
I have an interesting problem that maybe someone can shed some light on for me.......

I went to a customers pizza resturant for to check out a fan that he said he wants to slow down. Its a 208 1p 1 1/2 hp motor on this ventilation fan. Its blowing so fast its hard to open the doors when it on! I need to be able to slow this fan down with some sort of speed control. I know they are available for a 120v fan, but what about 208?

I was told i could use a frequency control, but thats over 400 dollars and more than the customer wants to spend. Would it be better to wire it for 120v, i was told that may slow it down some, and then i could add a 120v speed control to it, but obviously its more efficient @ 208v...........

I dont have much experience in this area of the trade and any input would be appreciated!!
 
It may be quicker to change the pulleys on the fan and or motor, if it is belt driven. pulleys are cheap and Grainger sells them.
larger pulley on the fan slows it down, smaller pulley on the motor slows it down.
 
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scottdbutcher said:
Hey Guys,
I have an interesting problem that maybe someone can shed some light on for me.......

I went to a customers pizza resturant for to check out a fan that he said he wants to slow down. Its a 208 1p 1 1/2 hp motor on this ventilation fan. Its blowing so fast its hard to open the doors when it on! I need to be able to slow this fan down with some sort of speed control. I know they are available for a 120v fan, but what about 208?

I was told i could use a frequency control, but thats over 400 dollars and more than the customer wants to spend. Would it be better to wire it for 120v, i was told that may slow it down some, and then i could add a 120v speed control to it, but obviously its more efficient @ 208v...........

I dont have much experience in this area of the trade and any input would be appreciated!!
Click to expand...

Changing the voltage would not change the speed. I would cause the motor to draw more amps and you would have to rewire the ckt. A variable frequency drive would work but its likely more that $400. As mentioned, changing the pulleys is the cheapest solution.
 
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scottdbutcher said:
Hey Guys,
I have an interesting problem that maybe someone can shed some light on for me.......

I went to a customers pizza restaurant for to check out a fan that he said he wants to slow down. Its a 208 1p 1 1/2 hp motor on this ventilation fan. Its blowing so fast its hard to open the doors when it on! I need to be able to slow this fan down with ...

I don't have much experience in this area of the trade and any input would be appreciated!!
Click to expand...
I suggest that you contact the fan manufacturer. There are some interesting characteristics of fans that may make your customer happy. If you partially block the inlet, with many designs you can reduce the flow maintaining the static pressure capability which may be needed.
 
bob said:
Changing the voltage would not change the speed. I would cause the motor to draw more amps and you would have to rewire the ckt. A variable frequency drive would work but its likely more that $400. As mentioned, changing the pulleys is the cheapest solution.
Click to expand...

The ASD could pay for its installation cost in less than a year. Pulley will operate the motor at less speed, but it will actually put the motor in a less operating efficiency region and does not save as much as the ASD. With the pulley, you either have to guess or calculate the air velocity to size the pulley correctly. With ASD the adjustment is continous and (practically) infinite. To get fancy you can add a draft gauge pressure transmitter to speed up the fan when the exterior door(s) opened.
 
Another option to look into is replacing the motor with a 120v one. If the amp draw isn't too much, you may be able to use a fan control then.
 
Yeah the pulley idea works...... the thought didnt even cross my mind! Sometimes the best solutions are right in front of your nose and you dont even see them! I can pick up some pulleys cheap, vfd is out of the question. Thanks guys, a little extra input always helps:wink:
 
Very few VFD's output single phase, so you would probably have to change your motor in order to use one.
 
I'd suggest considering the point that Laszlo makes. That fan could easily use $500 to $2000 worth of electricity over the course of a year. (Say it uses the full 1.5 HP for 8 hours per day and electricity costs $0.10 per kwh.) Properly implemented VSDs on fans can pay for themselves very quickly.

That said, you would have to do the numbers, and there may be several deal killers. For example, you have a single phase motor...generally you need a three phase motor to work with a VSD. Changing the motor means $$. The motor may not run for an extended period of time, and not get the hours in to pay for significant energy savings. There may be no benefit to being able to adjust the speed. Etc.

Finally, for small blower applications, you often can get significant speed change simply by changing the supply voltage. I'm sure that the $15 Lutron fan speed controls that look like dimmers are not VSDs, after all. You would need to check with the manufacturer, but the motor may be specified for operation at reduced voltage.

-Jon
 
jim dungar said:
Very few VFD's output single phase, so you would probably have to change your motor in order to use one.
Click to expand...
That thought ocurred to me too. The VFD might be an elegant and energy efficient solution but if you then have to supply, fit, and rewire the installation to accommodate the new motor and new VFD. I can see that it might not be an attractive proposition for the owner of the pizza place.
The pulley idea might be. Cheap. Quick. Effective. And harmonious with the business model.
:wink:
 
winnie said:
I'd suggest considering the point that Laszlo makes. That fan could easily use $500 to $2000 worth of electricity over the course of a year. (Say it uses the full 1.5 HP for 8 hours per day and electricity costs $0.10 per kwh.) Properly implemented VSDs on fans can pay for themselves very quickly.

That said, you would have to do the numbers, and there may be several deal killers. For example, you have a single phase motor...generally you need a three phase motor to work with a VSD. Changing the motor means $$. The motor may not run for an extended period of time, and not get the hours in to pay for significant energy savings. There may be no benefit to being able to adjust the speed. Etc.

Finally, for small blower applications, you often can get significant speed change simply by changing the supply voltage. I'm sure that the $15 Lutron fan speed controls that look like dimmers are not VSDs, after all. You would need to check with the manufacturer, but the motor may be specified for operation at reduced voltage.

-Jon
Click to expand...

Here is the data sheet for a Leeson single phase drive.
 
Misleading...

Misleading...

The Leeson drive literature is a little misleading IMHO.
Leeson said:
Can be used with induction, permanent split capacitor, shaded pole, synchronous and single-phase motors.
Click to expand...

That should read;

"Can ONLY be used with single-phase* permanent split capacitor and shaded pole induction* and synchronous motors."

*(changed position in sentence)

More to the point, you CANNOT use them on Split-Phase and Cap-Start / Cap-Run single-phase motors, which comprise probably +75% of single-phase motors in applications such as the one described. And more importantly, 99% of people who want to use them have no idea what type of single-phase motor they have. If they use these VFDs on the wrong type, they smoke the VFD and the motor, which coincidentally are both sold by Leeson...
 
weressl said:
Here is the data sheet for a Leeson single phase drive.
Click to expand...

Thanks, I knew 1-phase output ones existed some place.
Too bad it only goes to 1HP and the OP needs a 1-1/2HP unit.

And like jraef said:
you CANNOT use them on Split-Phase and Cap-Start / Cap-Run single-phase motors, which comprise probably +75% of single-phase motors in applications such as the one described.
Click to expand...

In particular, capacitors do not like it when their centrifugal switch does not remove them from the circuit. And run capacitors seem to like 60hz the best.
 
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winnie said:
I'd suggest considering the point that Laszlo makes. That fan could easily use $500 to $2000 worth of electricity over the course of a year. (Say it uses the full 1.5 HP for 8 hours per day and electricity costs $0.10 per kwh.)
Click to expand...
For eight hours a day, 365 days a year at 1.5 HP assuming 85% efficiency, electricity cost per year would be about $330.
If the fan could be run at say, half power by speed reduction, savings would maybe be around $150 p.a.
That might be a hard sell to the pizza place owner if, as the OP suggests, the VFD costs $500 and possibly installation and a new motor on top of that.
 
help on speed control systems

help on speed control systems

hello, i am a student studying electrical engineering, i have a question for an assignment asking me to "describe the construction and operation of a speed control system for a dc motor and how could the design be enhanced to provide directional control of the motor", my teacher has not covered this with my class as it is for a higher grade and we have to research it ourselves, problem is that i have looked all over on the internet and havnt been able to find any useful information, could you help me with this please or provide me with some useful links
 
If the problem is really the door stuck shut why not simply put a damper in to reduce air flow thus reducing the vaccume in the room. Seems a lot cheaper.
 
The fan is starving for air to move.... You may have to slow it to the point of uselessness
 
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