DavidS (Customer) asked a question.
Using a stepper motor as a fan motor???
I am thinking about using stepper motors as variable speed fan motors?
Our application uses a prop fan ~200mm in diameter, with fractional ECM motors. The ECM motors do not have the variable speed range down at the low end.
Our product already is using a Brx PLC, so running a stepper is easy. All we need is one direction, with speed control. Looking for speeds down to 30 RPM, which is not an issue with a stepper, but not available with variable speed ECM's/
BTW - We are moving cool air, so the motor will be in the cool air stream.
Looking for thoughts and comments, why this idea, might or might not work.
Thanks
David S
That's a somewhat unusual application but should work as long as you stay in the torque / speed limits of the motor. Once you slip at all it most likely won't resync until you come to a stop. Use a nice controlled accel / decel.
"Looking for speeds down to 30 RPM, which is not an issue with a stepper, but not available with variable speed ECM's/"
Steppers tend to have some vibration and loud, low frequency noise from steps being so far apart when running at a low speed like that. It is possible, but just something to think about whether that is an issue for you or not.
Steppers have excellent low speed torque, but it drops off significantly at high speed, where a fan would require the most torque.
If you have a stepper that will drive the fan at max speed, great, but I would suggest a three phase motor with a vfd.
Thanks for all the great answers. The fan motors we use are typically 15watt (@120VAC) total power. Not sure how that would translate to a stepper and one would convert a stepper's ratings to continuous watts of a running motor???
What's your top speed?
1500 RPM. Very rare if ever, would we need this speed. Most of the time it would be under 1000, probably more like 750.
That's a pretty wide speed range, like David_H mentioned stepper torque rolls off quick rapidly generally above 300-600 rpm (a lot of other factors). I would look at the torque / speed range of the motor based on what voltage you're able to feed to the drive. The higher the voltage the better.
Personally if you have the motor and drive I would just try it and see how well it runs at that speed. If you can reach that speed, try and apply some friction to the blade hub and see how easy it is to cause a stall.
Any idea what torque you'll need with that blade at that speed? Also, any idea of what motor / drive?
"The fan motors we use are typically 15watt (@120VAC) total power. Not sure how that would translate to a stepper "
15W is a pretty small motor, so I don't think a stepper will be a problem (except for possibly noise issues)
While for conventional motors electrical power is fairly close to mechanical power, that is not the case with steppers. Especially at low speeds the efficiency of a stepper can be very low, so multiplying current by voltage will give a very poor idea of mechanical power (and since the coils are a reactive load it will probably not give the real electrical power either)
Now, if you happen to have the torque rating of the existing motor is is easy, while it is true that as David H says, stepper torque drops with speed, on Automation Direct's web site they have a stepper selector utility which can select for performance at certain speeds.
If you don't have a torque spec. for the current motor, one can make an educated guess. Assuming your "15W" is the mechanical power output (if actual power is less that just makes the torque estimate more conservative) 15W is 15 joules per second, at your 1500rpm there will be 25 revolutions per second. Google tells me 15 joules is about 11 ft-lb (note that ft-lb torque and ftlb energy are different things)
the above mentioned motor selector uses oz-in, which is one ounce force on a one inch long lever arm. A one inch radius arm makes a two inch diameter circle if rotated a full revolution, 2" times pi is a bit over 6" or 1/2 ft, for the 25 revolutions the motor makes in one second (at 1500rpm) that is one ounce of force over about 12.5 ft., conveniently close to the 11 in the 11ft-lb we found above, as there are 16 oz. in a pound, we can try 16 oz-in at 1800rpm (selector doesn't have 1500. but using 1800 gives a better safety factor so that's OK) on the selector at: https://www.automationdirect.com/selectors/steppers and we find that a LOT of motors fit.
Tinker - Thanks. I will dig in, select a motor, and do some testing!
That's weird - looks like some comments were deleted.