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Explosionproof motor with fan
Explosionproof motor w  
QUESTION: Hello I have a Dayton single phase split phase motor quarter horsepower 115 V at 4.5 A this is an explosionproof fan and motor I would act like to add a speed control to the motor how would I go about doing that?

ANSWER: Chuck, the motor looks new, I don't see the XP tag,   what Group and Class is the motor rated for?  Or why is the motor required to be XP?

I ask, because if the control is intended to be in the same environment, the control would need to match the same Group and Class as the motor is rated at.

How much speed control do you need? You realize no matter what you do, with a split phase single phase motor,  it is going to be limited in range.  If you change the speed it is going to change the torque and HP with the variance in speed.

Your best bet is to look towards controlling the line frequency,  that will give you the least amount of loss of power,  and I am assuming you want speed control below and up to the base speed?

Anything above the base speed, is going to take design evaluation, of the entire fan system in much greater detail then if the desired speed change is lower than the base speed.

No matter what you do, this is NOT going to be something simple like installing a light dimmer.

There are so many limitations to varying single phase motor speed,  it is often not cost effective and extremely limited in range.

Changing the fan output by mechanical means,  might be a more effective method than changing the speed of the motor itself.

There are commercially available frequency drives that would change the speed,   but again even then the range is limited,  along with the relationship between HP, torque and speed.

This really needs to be looked at as a SYSTEM, there is no simple answer to variable speed on a motor that was designed to run at the nameplate speed.

It comes down to varying the applied voltage, or varying the applied frequency.

It really depends on the whole of the fan system,  the reason for the need to change speeds, and the range of speed needed, along with the XP environment, as anything that is involved with the motor will have to match the motor UL XP rating.

You will want to read the below link,   there are comments on speed control,  and your situation is even more complicated with the need for XP ratings.

and then this link:

If you truly need variable speed FROM THE MOTOR SPEED,  this install should have been designed from the beginning to be variable speed and explosion proof on top of that.

Honestly I would need to know the entire desired outcome and environment to even begin to suggest the most cost effective and realistic approach.

Do you meed variable speed, or could the application work with speed CHOICES?

If you could live with speed choices,  a multi-speed motor would be a better choice.

If you need variable speed, and can stand the change in torque and HP, the best way to get there is with three phase.  With a three phase motor,  you could  use a single to three phase converter type variable frequency drive.   Normally that type of setup is much more efficient than attempting to vary the speed of a motor that is not intended to be changed or varied.

Which brings us back to the same issue,  where will the controls be located,  and all that is involved with this fan in an environment that requires components that will operate in whatever type of explosion possible environment.

I am going to need more information to point you towards a solution.  Again if the volume of air can be controlled by mechanical means,  it is going to be a much better solution than attempting to vary the speed of a motor that is not designed to be varied.

Even swapping this motor out for a three phase motor with a convertor and frequency drive is only going to provide limited control.

Is the speed going to run mostly at a lower speed,  or mostly at the rated speed?  If the fan needs to run at a lower speed, then the base speed of the motor might need to be changed.

Bottom line,  this is a situation where the need for variable output of the fan should have been designed as a system up front, versus attempting to change the speed of a motor that is not going to provide much speed change regardless of what method is selected.

Write me back and give the details of the system, the type of XP considerations, and let's start there.  With this motor varying the speed is going to be a difficult and limited range, along with the noise, and varying performance curve.

Maybe some type of variable mechanical drive before the fan would be a better solution.  Even a variable pitch belted pulley would be a much simpler option than varying the speed of the motor.

---------- FOLLOW-UP ----------

Xp fan motor
Xp fan motor  
QUESTION: Sorry for not getting back sooner, Yes this is a XP rated motor I would like to use this in my 2 car garage for painting , fumes and heavy dust removal as you can see by the pic the fan is solid aluminum and at 1750 rpm the amount of noise might be to much ! And the volume to high so half speed not like a Potentiometer but a SWITCH to half the speed I was told that changing the freqs would overheat the motor. Can I reduce the speed electrically if not is there another cheap way of exhausting paint fumes for a 2 car garage ?

Sent from Chuck

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Hello I have a Dayton single phase split phase motor quarter horsepower 115 V at 4.5 A this is an explosionproof fan and motor I would act like to add a speed control to the motor how would I go about doing that?

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Chuck with split phase,   the motor has a starting winding, and run winding,  the run winding cannot be slowed in half or it will drop into the start windings,       

This is a great idea, most people never consider wood dust is explosive, but the motor you have is the worst to speed control  actually you will get next to no range of speed control    frequency can cause heat because the fans dont turn at the designed speed,    all this speed control has issues that need to be considered,    

Can you do this,   maybe use two fans, one slower and one faster or both together?

Other tan that for 50% reduction three phase is your only way or get a two speed single phase with two speeds that one is twice the other,       but trying to do control with a split phase is just really a waste of time,      

But at least you are wise enough to vent the stuff out and not blow yourself up,   one of the few who have even thought about it,         

I would check prices on either another motor,  at a lower speed, and use both how you need them or go three phase,   and if you need half speed   up rate the motor to 1/3 or 1/2 so you can slow it down,    by half,  

then compare that to a two speed single phase XP and see what kinda of cost you are looking at,  we get little in single phase XP,      you might consider a blower not a fan,   and put the motor outside somewhere with only ducting in the structure      sometimes that works  and then you dont even need the XP     

How about sitting a caged blower out of the structure  like a furnace,   by the time it is drawn to the blower   it is so diluted there is no explosion concerns,     I would look in those directions, and if you cannot find anything    use my private email  and we figure something out,  

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Three phase/ AC DC single phase motors, controls, any problems or failures, motor installation, performance issues, connections. All other electric motors/gearboxes/apparatus. Specialty repair concerns, obsolete motors and solutions. Other mechanical or specialty equipment. See my profile under Home/electrical at this site


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