Geo-TH,In

Well-known Member
I've seen 1/4 hp shaded pole blower motors on a furnace, which should only use about 200 watts, less than 2 amps, draw 8-10 amps. The reason, the shaded pole motor isn't powerfactored. In theory if it were powerfactored, it should draw close to 2 amps, right?

Our residental electric meter can only sees the 2 amps, even if motor isn't PF. Am I right again?

A shaded pole fan motor generates a lot of heat. In theory, the heat produced is calculated by I squared R. So, is the heat produced inside a shaded pole motor based on the 10 amps or the 2 amps? If it's the 10 amps and our energy meter only sees 2 amps, are we getting more heat energy than we are paying for?

JohnT, Yes, this question goes to show you I have too much time on my hands.
George
 
An electric motor will draw whatever power it needs for its load, up until it stalls. So it's possible for a 200 watt motor to draw more than 200 watts. And since most motors operate at less than unity power factor, the volt-amps will be greater than the watts. That said, if a 1/4 horsepower 120 volt motor is drawing over 8 amps, something is wrong. Power factor alone isn't sufficient to account for a 1/4 hp motor drawing nearly one kVA.

Electric meters measure watts, not volt-amps. So in general a low power factor won't cost you extra.

I<sup>2</sup>R losses are calculated by actual current. You can't reduce I<sup>2</sup>R losses inside the motor by correcting for power factor (e.g. by adding a PF correction capacitor), because the power factor of the motor is unchanged; only the power factor presented to the power source is changed.
 
The purpose of the shaded-pole is to start the motor as single -phase induction motors require some type of starting assist. The shaded-pole remains during all stages of operation and wastes significant power in the form of heat. The primary advantage of shaded-pole motors is that they are cheap to manufacture. They have no centrifugal switch for the starting windings-- and they have no separate starting windings.
1/4 hp is really large for shaded-pole, larger than any I have ever seen, as many of them are 1/10 hp or less.
If it draws more than nameplate amperage, it is overloaded in some fashion.
 
Bus wrote: "1/4 hp is really large for shaded-pole, larger than any I have ever seen"

They were common in older mobile home furnaces (CHEAP)... even 1/3 and possibly 1/2 HP!

Wayne submersible sump pumps (and likely others) use at least up to 1/2 HP shaded-pole motors.

Wastes a LOT of power, but eliminates the need for a starting switch or capacitor and the troubles that could go along with those items being in the oil-filled motor, and underwater!
 
Good morning "Curious George" and I mean that as a compliment, I remain curious about this "lectricity" stuff myself. Its been over 40 yrs since my first EE job with The Century Electric Motor Co but heres my best recollection:

1) "I've seen 1/4 hp shaded pole blower motors on a furnace, which should only use about 200 watts, less than 2 amps, draw 8-10 amps. The reason, the shaded pole motor isn't powerfactored."

I think the reason is the shaded pole winding (unlike if a centrifugal switch cut it out at X RPM) remains in the circuit drawing extra current and producing heat even though its function is long over........


2) "In theory if it were powerfactored, it should draw close to 2 amps, right?"

Not sure what you mean by "powerfactored" Indeed if the start winding were cut out of the circuit via a centrifugal switch, there would be less current draw thereafter and such would relate to the motors single phase induction and HP and load BUT NO LONGER THE EXTRA START WINDING.


3) "Our residental electric meter can only sees the 2 amps, even if motor isn't PF. Am I right again?"

NO the electric meter sees the total amperage which consists of BOTH what the run winding draws PLUS what the paralell shaded pole winding continues to draw (cuz no switch cuts it out at X RPM)

3) "A shaded pole fan motor generates a lot of heat. In theory, the heat produced is calculated by I squared R. So, is the heat produced inside a shaded pole motor based on the 10 amps or the 2 amps? If it's the 10 amps and our energy meter only sees 2 amps, are we getting more heat energy than we are paying for?"

The heat produced is I Squared R AND THATS THE TOTAL I (Run PLUS Start Winding)

NOTES: Many cheap shaded pole motors like say for a ceiling fan application have very low starting torque and can hardly pull a rubber chicken, but thats NOT to say that start winding cant be bigger and have more coils of wire and produce much more starting torque if such is required (Shaded pole is NOT ONLY for small fan motors). The "shaded pole" is another winding in addition to the run winding which is magnetically offset from the run winding so the motor knows which way to start spinning plus actually starts turning that way ITS JUST THAT IT REMAINS IN TEH CIRCUIT unlike a split phase induction motor where a centrifugal switch cuts it out once started.

NOTE Power factor is the cosine of the angle between current and voltage. If the load is pure resistive (Not L or C) they are in phase and the cosine of 0 degrees is one A UNITY POWER FACTOR.

NOTE A motor is mostly an Inductive load and in an inductor the Current lags the Voltage thus they are NOT in phase so theres a less then unity power factor. If a capacitor is placed in the circuit (Voltage lags current) that helps balance out the current and voltage bringing them back closer to sync and improving power factor.

I think youre confusing power factor and all that real versus apparent power stuff and phase angles of voltage and current versus the total current a shaded pole motor draws even after start up......

Nuff for now, I gotta take my dear old 90 yo mother to a Dr Appointment, back this evening.

John T
 
JohnT,
Hope momma is doing well. Before my mom died at 88, I made many trips to Florida to watch her. It was a blessing she passed on Easter Sunday 3 years. No one should have to live with cancer and all the pain she went through.

Follow up question. I'll try to make it simple.

My 3/4 hp water pump on 110v will use about 12 amps. I put 200 MFD's in parallel with motor and dropped the current to 9 amps. Measured PF, it's 0.99. The motor still draws 12 amps, the line current going to motor is 9 amps.

It's my understanding that with or without the cap bank. My electric meter only sees the 9 amps and not the 12 amps. Is that correct?

There will be a follow up question.

"Curious George"
 
To those who say they have seen shaded pole 1/4 or even 1/2 hp motors, what I know for certain is that I have not seen any of that size. A link to a website would be helpful.
Shaded-pole motors have very low starting torque and loads that require 1/4 or more hp probably could not be started by the shaded pole.
It seems that split-phase might be the type that was actually encountered. Very common for 1/4 and 1/3 hp loads that are relatively easy starting. I have a shelf full of those in my shop. And most single-phase motors of 1/2 hp or more will use capacitor starting.
Unless I see an actual "official" reference to larger shaded pole motors, I simply cannot believe that they exist. My beliefs, right or wrong, do not change reality.
 
Hey George, I, as you know, meant no offense with the "curious George" nickname. Heck I'm curious as a cat myself and seems my kids years ago watched a cartoon about some curious George, character, but I'm not sure.

Not having your meter or any specs or anything at all, its still my "best guess" you're correct, it sees the amperage which would be that if you had a unity one power factor, which means it does NOT see the vector sum of the resistive current component flow PLUS the Inductive (out of phase if not corrected) component. The electric company watt hour meter doesn't take power factor into consideration far as I know (44 years ago Duncan Meter Co gave a talk in our EE school but Ive slept since then) HOWEVER at the place I worked they still monitored Power Factor (even if meter didn't show) and charged us a huge penalty if we were off Unity by too much........

Tell you what, my friend the good Buick man (unlike long retired me) is very active in this business and knows this power factor stuff better then me, but its still my guess your meter DOES NOT SEE or take power factor or out of unity power factor current into consideration. See what he and the other more current in the practice sparkies have to say NO WARRANTY on my best guesses about how your particular meter works.

See, Im as curious as you are and always willing to learn.......

A rusty OLD John T
 
JohnT,

No offense taken.

So, if I got things right in my head, with or without caps, the motor uses the same current and generates the same heat.

The only thing that benefits is the circuit breaker in the load center is seeing less amps and there is less I squared loss in the wire going to the motor.

What about a generator? Is it better for a genny to PF?

George
 
"So, if I got things right in my head, with or without caps, the motor uses the same current and generates the same heat."

I cant say that's exactly right, but its hard to explain and I'm way too lazy to dust off my books lol. Here's what I will say, however. If the PF is unity meaning, the current isn't leading or lagging the voltage, its in phase, the vector sum of the resistive current component and reactive (L/C) current component is the same as the resistive ONLY i.e. C canceled out the L. However, if the PF is less then unity, the current is the vector sum of the 2 out of phase components (R + L/C) even though a meter doesn't take that into account, its watts NOT Volt Amps.



"What about a generator? Is it better for a genny to PF?"

The utility or a genset generates a sine wave and it has to "work" less if the load is unity PF. If the PF is lousy the genset or utility is actually having to produce the in plus out of phase current components (vector sum) and that's why we were charged a penalty for a lousy PF even though our watt hour meters registered the same

HEY GEORGE IM RUNNIN OUTA SMARTS ON THIS PF STUFF this is my best recollection but certainly not warranted correct. When I believe an answer is correct I just state it, but Im NOT sure on this PF stuff, its been too long, dont take any drastic steps based on the above, consult someone more current in the trade whose not been retired over 20 years ........

Sorry, but that's all I got

John T
 
Hey Driver man, sorry I have no specs or data or info on any bigger then small fan shaded pole motors youre asking about. However I can tell you the ones designed for small low torque fan or blower motors dont have a very big winding because 1) It dont take much magnetic field strength to get it spinning and 2) They dont want to waste any more energy then necessary since it sits there and wastes energy even after running as it dont get switched out. HOWEVER theres no reason they couldnt have a bigger winding that draws more amps that develops more magnetic field to produce more start up torque that remains in the circuit so no switch is involved BUT THATS NOT AS EFFICIENT AS IF THAT BIGGER WINDING GOT SWITCHED OUT.

However, Im sure you already know all this and are just curious to see specs and data for higher torque requirement bigger HP shaded pole motors and I sure dont hold that against you. I learned years ago NEVER SAY NEVER so I don't say they are or are not available (likely are is my bet) but a place where you didn't care if they were less efficient because they were hard to get to and you don't want to mess with any switch headaches (like a well pump motor Bob mentioned) sure would be a good candidate lol

Fun chattin with ya

Merry Christmas

John T
 
John, I know power engineering was your speciality, and I've never worked in the field. But I'm fairly sure kwh meters measure actual power, not volt-amps. The traditional mechanical meters have both voltage and current windings; if current and voltage are out of phase, that will be reflected in the number of watt-hours recorded by the meter. I think the newer "smart" meters can record not just kwh, but average current, voltage, power factor and a bunch of other stuff.

Of course, utilities can and do penalize customers with low power factors. Look at it this way: if the power company could charge based on volt-amps rather than watts, they wouldn't be too concerned about customers with poor power factors.
 
Hey there Mark, Actually AC Power Distribution was more my specialty and while I worked a lot with Power Factor and Power Factor Correction, Im very rusty in that area as well as the types of modern or "smart" KWH Meters etc. Like I used to tell my kids "Old dad knows some things but NOT everything" HOWEVER the things I DID SAY about what PF is and its definition etc is I believe accurate.........I may have to break down and refresh myself in this area but Im too lazy and old for that. The "stuff" I do know I'm glad to share and help people with as you well know.

John T
 
thanks JohnT,
I am very familar with vectors, series and parallel tank circuits, XL, Xc, R, Z, all the equations in electronics. Never really applied them to motors.

What I'm not 100% sure of, but going to take a guess an educated guess on what you call unity(powerfactor).

When the phase angle between the vector sum and R is zero, the cos of zero is one and the Power Factor is 1, unity.

So, if you were to find the phase angle then the cosine of that angle transulates to the power factor. example. The phase angle is 45 degrees, the cosine of 45 is .707. Therefore you would say the power factor is .707. As the phase angle approaches 90 degrees, the power factor approaches 0. As phase angle approaches zero, power factor approaches 1.

If you can follow this chatter, good luck.

Yes. I have too much time on my hands.

So, is the cos of phase angle = power factor.

Inverse cosine of power factor = phase angle.

I'm kinda of rusty too. Only been retired 10 years. I pitched all my books.

George
 
"So, is the cos of phase angle = power factor. "

YOU GOT IT.........And if they are in phase the angle is zero and the cosine of zero is one...

Fun huh

John T
 

Thanks for the info. I too had always thought of shaded pole motors as very small fractional hp motors.

Dusty
 
BOTTOM LINE as Ive learned and said here before:

NEVER SAY NEVER AND NEVER SAY ALWAYS if you do someone will jump out and prove you're wrong lol

DISCLAIMER: Theres a chance this may or may not be correct and Im NOT saying it is or it isn't.......

John T
 
JohnT,
Don't think I ever read that any place. Why do some try to make it so complicated?
George
 
Bob,
Mobile home furnaces is where I saw 1/4 hp shaded pole motors. Think I've even seen cheap grinders with large shaded pole motors.
Once I saw a shaded pole fan, reversable. Used wires for shade and by connecting wires together and opening the other side motor would revers.

Some people think that just because they haven't seen something, it doesn exist. There is a lot to be learned if Everyone keep an open mind.

George
 

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