Power factor / efficency of shaded pole motors

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iwire said:
I would think in most buildings there is much more lighting that is on more hours than the motors so they are going after the easy first.

On the other hand in each of the supermarkets I work for they have 100s of small fan motors that run 24/7. They did go around and swap out the motors for much higher efficiency motors.
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I've heard of cases where they reduced the voltage on these small motors by 5-10% and it lead to good savings. Arent there supermarkets out there that take the approach going as far to the main service?
 
mbrooke said:
I've heard of cases where they reduced the voltage on these small motors by 5-10% and it lead to good savings. Arent there supermarkets out there that take the approach going as far to the main service?
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Voltage regulators. http://www.microplanet.com/products/end-user

I installed some that handled 100% of the load at one of our customers stores to see if it worked out. It has been about five years and they have not installed them in any other locations.
 
mbrooke said:
Did it work out in that particular store?
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Considering that chain is continuously doing energy savings projects and they have not installed anymore of these I would have to assume no it did not work out.

They have also tried cogeneration fuel cells but those have been removed, to much downtime, up keep and costs to justify.
 
The most RPM you can get from 60 Hz with a motor is 3,600 RPM. The next lowest is 1,800RPM. 3,150 RPM someone posted means 2 pole motor with a 12.5% slip at the rated load.

Induction motors are not inherently adjustable speed without changing frequency. You're changing transformer taps when you select different speeds on multi-speed motors like box fans and air handler motors. It slows down by increasing the slip between the rotor and the field. Power savings involving fans is also secondary. A fan that takes 1 hp to turn at 3450 RPM only uses 0.875 hp at 3350 RPM even though the RPM is only 4.6% lower. The significant saving in fans come from slowing them down while keeping in control.

As you slowly lower the voltage on a partially loaded standard motor, you'll hit a point where the RPM begins to plummet. Just ahead of here is where you get the best efficiency. It's not easy to use passively because you'll lose starting torque and maximum load at reduced voltage. Some VFDs include this kind of active control. If load is placed on the motor, it has to be able to quickly bring the voltage up to prevent stalling out.


A desktop PC is designed to keep within safe temperature with full CPU load across the entire rated ambient conditions. Very old computers ran fans at full speed. Modern systems use variable speed fan which basically never reach full speed unless you're running them at full load in a 90F room. This saves like 10-15W per computer which is significant given the quantity of them in corporate offices and the duration. They're doing something similar with condensing unit fans.
 
Phil Corso said:
The Shaded-Pole motor's speed can be controlled with voltage!

Phil
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mbrooke said:
Explain... At this point I am thinking a know nothing about shaded pole motors. :huh: And yahhh, that 3150RPM on GE's induction motor has me asking the same question.
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My response was: It slows down by increasing the slip between the rotor and the field.
3150 RPM is 3150/3600 =0.875. Meaning a 2 pole with 12.5% slip. A standard induction motor is 3,450. A synchronous motor is 3,600 RPM.
The magnetic field is always 3,600 RPM for 2 pole.
 
And because a shaded pole has low torque characteristics to begin with there naturally have a lot of slip. A two pole shaded pole motor still has a synchronous speed of 3600 if running at 60 Hz. Lower the voltage and you lower the already low torque and actual speed will decrease, but the motor current doesn't increase all that much if any compared to other motor designs if you lower the input voltage. As mentioned already they naturally have low power factor and low efficiency compared to other motor designs.
 
mbrooke said:
Explain...
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Although both typical and shaded-pole motors are considered to be induction machines there is considerable difference in how each produce torque! The former’s torque is rather smooth over a complete cycle, while the latter’s varies because of its construction. The stator-winding is similar to that of a Series-winding machine, i.e., having salient-poles!

If you need more I can cite texts used when I taught “Electrical Technology”, while pursuing an Electrical Engineering career!

Phil
 
Phil Corso said:
Although both typical and shaded-pole motors are considered to be induction machines there is considerable difference in how each produce torque! The former’s torque is rather smooth over a complete cycle, while the latter’s varies because of its construction. The stator-winding is similar to that of a Series-winding machine, i.e., having salient-poles!

If you need more I can cite texts used when I taught “Electrical Technology”, while pursuing an Electrical Engineering career!

Phil
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Salient poles? :?
 
Salient pole machines use permanent magnet rotor or variable strength electromagnet (with wound rotor) and stay together the same as magnetic aquarium algae scrubber. If the load becomes excessive, they disengage.

Normal induction motor works like dragging a powerful magnet very quickly across an aluminum bar. There has to be a speed difference to produce torque.
 
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