Resource for average load for low-HP motors

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calebtinkers

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I'm working on verifying some estimates around energy savings delivered by some motor replacements, and to support that I need some kind of assumption about what the old motors drew. In this case, I'm looking at 1/20 HP shaded pole motors, and looking for a reliable 'industry standard' table that shows the average actual operating wattage once the motor is started and running. I'm also interested in 1/3 HP and 1/47 HP.

Can anyone point me in the right direction?
 
The running load will be based on the actual physical work the motor is doing. The same motor will have vastly different power consumption based on the HP (work) being supplied to the load.
 
don_resqcapt19 said:
The running load will be based on the actual physical work the motor is doing. The same motor will have vastly different power consumption based on the HP (work) being supplied to the load.
Click to expand...

Thanks for helping me out! I was kind of assuming that all 1/20 HP motors would always have 1/20 HP supplied to that load, since my understanding was that shaded pole motors are one speed, and I figured that 1 speed meant one work-level. Am I missing something?
 
I think you are missing the actual physical work the motor is doing. Even a different pitch or diameter of a fan blade attached to the motor shaft will result in a different amount of work, and a different load.
The motor rating is the HP that it is designed to supply...has nothing to do with the actual load other than if you try to drive a load that requires more HP than the motor can supply, it will trip its over load device or stall.
 
don_resqcapt19 said:
I think you are missing the actual physical work the motor is doing. Even a different pitch or diameter of a fan blade attached to the motor shaft will result in a different amount of work, and a different load.
The motor rating is the HP that it is designed to supply...has nothing to do with the actual load other than if you try to drive a load that requires more HP than the motor can supply, it will trip its over load device or stall.
Click to expand...

Understood. Thanks so much for the guidance!
 
Shaded pole is likely going to be less efficient than most other motor types. It is an inexpensive motor design but not that efficient. But depending on application may still not be worth investing in other motor types. Something that runs continuously may be worth investment, something that doesn't have much run time may not be worth the investment.
 
Efficiency is generally terrible for all fractional horsepower and all single phase motors. That’s why you tend to see various DC, electronically commutated, and servo motors in use in high efficiency HVAC for instance, but at a cost that is only justified with a large air handler.
 
Shaded Pole AC motors are notoriously inefficient, in the neighborhood of 30% down to as low as 15% efficient. The only reason people use them is because they are cheap to make and very simple, so very reliable. Nobody picks an SP motor because they are concerned for efficiency, they are in fact the WORST of anything available..
 
I think your best way to approach this is look at various 1/20 HP shaded pole motors, get an average amp rating, and compare same in a PSC motor. You will probably see about a 50% savings.
 
calebtinkers said:
..... shaded pole motors are one speed, and I figured that 1 speed meant one work-level. Am I missing something?
Click to expand...

To expand a bit on don_resqcapt19's post, when you look at _power_ you will always find it is the product of two things.

Electrical power is volts times amps.
Hydraulic power is pressure times flow.
Etc.

For a spinning electric motor, mechanical output power is torque times speed.

Even with a fixed speed, different mechanical loads will have different torques, so the mechanical output power of the motor changes. In general the electrical input power will reflect changes in the mechanical output power.

Shaded pole motors may be so inefficient that changes in load might be masked by the losses in the motor itself. Here is an example of a 'shaded motor performance characteristic' that I found. Over the entire load range input current is pretty constant, input power varies from 21 to 30 watts, and efficiency goes from zero (at no load) to 20% at full load.

Jon
 
winnie said:
To expand a bit on don_resqcapt19's post, when you look at _power_ you will always find it is the product of two things.

Electrical power is volts times amps.
Hydraulic power is pressure times flow.
Etc.

For a spinning electric motor, mechanical output power is torque times speed.

Even with a fixed speed, different mechanical loads will have different torques, so the mechanical output power of the motor changes. In general the electrical input power will reflect changes in the mechanical output power.

Shaded pole motors may be so inefficient that changes in load might be masked by the losses in the motor itself. Here is an example of a 'shaded motor performance characteristic' that I found. Over the entire load range input current is pretty constant, input power varies from 21 to 30 watts, and efficiency goes from zero (at no load) to 20% at full load.

Jon
Click to expand...

Small nit pick. It’s Volts times Amos for DC. For AC you must include power factor.

More to the point watts is watts, whether heat or moving air. We just want more of the latter and less out of the former out of a motor.

But keep this in mind too. For any motor they will all draw a certain amount of power that is converted into magnetic flux. This flux is a rotating magnetic field that pushes/pulls the rotor around. The flux does ZERO work...by itself it does nothing. So it draws a current but at ZERO power factor. Watts is zero. So with no load on a motor we will see a small loss due to operating the fan (if it has one), losses (heat) in the bearings, and losses as the magnetic core magnetizes and demagnetizes (core losses) also as heat. Under load the rest is torque current which is doing work so that is watts (power factor 1.0). Actual amps is all three (constant motor losses, constant flux current, variable torque current). In a large 3 phase AC motor the motor losses will be under 1% almost irrespective of the design. Even very old 200+ HP motors have less than 1% losses. Going to your shaded pole motor about 70% of the power is losses. So even a PSC motor is going to easily beat the shaded pole motor efficiency wise. The most efficient single phase motors are capacitor start/capacitor run motors. That’s for single phase, single speed. So if you are questing for high efficiency shaded pole motors, stop right now. Just switch to PSC or switched start capacitor motors now. Both types require extra parts external to the motor itself but it all easily fits in a space about the size of an old style NEMA starter.

For even higher efficiency and taking the process into account on small motors typically DC brushless motors with a DC drive are the highest efficiency currently. That is why they are used in high efficiency HVAC fans and high speed assembly lines and robotics. There are losses in the drive (about 5%) but it makes up for it with variable speed control. So for instance instead of running a fan at full speed and controlling air flow with a damper, an HVAC will use a variable speed motor and no damper, eliminating losses inherent in choking off air flow that vastly exceed the 5% losses except if it is operating nearly at 100%. Obviously this is a more complicated design because of two things. We’ve added electronics which are considerably more complicated than two capacitors and a voltage triggered relay. And inherent in a variable speed design we have some kind of process sensor (pressure, temperature, etc.) and turning that into a speed command. In an HVAC air handler that already costs thousands and runs 24/7, this much higher cost design probably pays for itself in under a year.
 
210314-1321 EDT

paulengr:

winnie's statement volts times amperes is power is correct. It is an instantaneous value. It can take on both positive and negative values over some time period. For clarity, when integrated and averaged, it means "real power", something that does useful work over some time period, not just stored energy.

Power is an instantaneous measurement. The integral of power over some time period divided by that time period is "average real power".

The equation you stated (V*I*PF = Real average power) is some sort of averaging measurement ---
is probably meant to mean Vrms, and Irms where these two values are stationary, not necessarily corrected with each other, and obtained over a sufficiently long averaging time to introduce little error, and multiplied by a "fudge factor", PF, to obtain a value close to the value obtained if you did the integral, and obtained its average value.

.
 
210314-1712 EDT

To continue.

If we assume a sine wave voltage source and a resistive load, then

instantaneous power is p = ( V * sin t ) * ( I * sin t ) where
V is the peak voltage of the sine wave
I is the peak current of sine wave thru the load resistance
t is an instant of time.

From this you see that power is not a constant, but looks like
p = V * I * sin^2 t

Average power over an exact 1/2 cycle is
P half cycle average = ( V * I / Pi ) * integral of sin^2 t from t=0 to t=Pi
P half cycle average = ( V * I / Pi ) * ( Pi/2 - 0 ) or
P half cycle average = V * I / 2, thus
P half cycle average = 1.414 * Vrms * 1.414 * Irms / 2 = 1.414 * 1.414 * Vrms * Irms / 2 = Vrms * Irms

.
 
210315-1506 EDT

LarryFine:

Getting back to some real world considerations.

How does the brainwork? I don't know. Do I think by the sequence of letters in a word? Clearly I think the answer is no. Does my brain work like yours, or someone else's? Probably not. Are there other brains that work like mine? Probably yes.

My great-grandfather was pure German from Freiberg, Black Forest region, very near France. My DNA shows German, but no French. His wife was from much further north. They both came to the US before 1850. My grandmother was pure German and born in the US. Thus, my dad was 1/2 German, and I am 1/4. My great-grandfather learned and spoke English, but apparently retained Germany structure. When my dad was young, possibly 6, and walking with his grandfather, the following words were spoken --- "out the pipe the mouth fall". Do I get some structure to my sentences from my German ancestors? Possibly.

Since I don't think in terms of the letters of a word that means there is a dictionary in my brain that translates some other form of information to letters in a word when needed, typing or writing. What is the fundamental form of the information in my brain that gets translated into letters of a word? I don't know.

In some ways I am in fairly good health. I walk on my own, go up and down stairs, fix my meals, I drive, and more or less take care of myself. Of the male population in the United States alive in 1930 less than 1% are still alive.

However, my heart rate went down into the 30s, I have a totally blocked heart artery, I had cataracts removed, and I may have a balance problem at times. I now have a two electrode pacemaker, so pulse rate does not drop below 60. My upper heart area gets pulsed only about 5% of the time, while the lower half is pulsed about 95%. I am on an extremely expensive medicine that's supposed help the electrical communication from the upper half to the lower half. My resting systolic pressure is around 100. My breathing rate is somewhat increased going up a flight of stairs. My BMI is in the low 20s.

My significant balance problem has occurred about 4 times. In all cases I was totally conscious. Two cases I got up, probably quickly, and had no left side control. I fell sideways. I had no ability to send information to the left side muscles to tell them what to do. This Thursday I will be seeing a neurologist to see if they can spot anything. I have previously had a CAT scan, and a radioactive scan, and I believe they can not do an MRI because of the pacemaker.

This may seem of topic, and possibly is, but might be useful to you. The human body is very much an electrical system.

I will be trying some other experiments on my shaded motor, but not immediately.

.
 
210315-2052 EDT

I have been doing some thinking on how I can run somewhat more controlled experiments on my shaded pole motor.

A typical induction motor has a foldback speed torque curve. After foldback is an unstable torque region for many loads.

So how can I provide a controlled load on the motor under test. My thought is this --- I have a moderately low speed torque test head
with a DC motor drive, and a rotating torque transducer. This can operate at a moderately constant speed up to its torque limiting level. That limiting value is adjustable up to a maximum value. If this is the load on the shaded pole induction motor, then I can specify the load speed of the motor under test as long as my DC drive is the controlling element, more torque capability than the motor under test.

Are the parameters of my test head sufficiently within range of my test needs? To be determined.

I already have a rough idea that I can only produce about a 25% change with voltage control of the shaded pole motor, and have stable operation.

.
 
210315-2350 EDT

LarryFine:

Not at all. My last post was just to keep the thread on course so somebody does not closes it.

I have no need to study shaded pole motors, but the subject has brought up some interesting questions. I think my oversized DC drive will provide some interesting information, and a useful technique. It is 65 years since I had any machinery courses, and I have only limitedly worked with AC or DC machinery. My AC Machinery book was written by one of the early pioneers in the study of these things. I never met him, but my guess is that my uncle had him as one of his professors. Back when my uncle was an EE student at Michigan there only about 5 or so EE professors. About 4 of these were also my teachers.

Overall in all subject areas I had some excellent teachers at the various schools I attended.

.
 
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