Posted by John T on December 16, 2013 at 04:57:56 from (216.249.76.176):
In Reply to: JohnT? posted by George Marsh on December 15, 2013 at 15:50:35:
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.
We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today. [ About Us ]
Today's Featured Article - The Ferguson System Principal An implement cutting through the soil at a certain depth say eight inches requires a certain force or draft to pull it. Obviously that draft will increase if the implement runs deeper than eight inches, and decrease if it runs shallower. Why not use that draft fact to control the depth of work automatically? The draft forces are
... [Read Article]
All Rights Reserved. Reproduction of any part of this website, including design and content, without written permission is strictly prohibited. Trade Marks and Trade Names contained and used in this Website are those of others, and are used in this Website in a descriptive sense to refer to the products of others. Use of this Web site constitutes acceptance of our User Agreement and Privacy Policy
TRADEMARK DISCLAIMER: Tradenames and Trademarks referred to within Yesterday's Tractor Co. products and within the Yesterday's Tractor Co. websites are the property of their respective trademark holders. None of these trademark holders are affiliated with Yesterday's Tractor Co., our products, or our website nor are we sponsored by them. John Deere and its logos are the registered trademarks of the John Deere Corporation. Agco, Agco Allis, White, Massey Ferguson and their logos are the registered trademarks of AGCO Corporation. Case, Case-IH, Farmall, International Harvester, New Holland and their logos are registered trademarks of CNH Global N.V.
