Punx0r said:Woah... Copper losses are proportional only to current (at a given temperature)...
You think there is no frequency component whatsoever in copper losses? Right.
Punx0r said:Woah... Copper losses are proportional only to current (at a given temperature)...
Seriously, pick up Kingsley and Fitzgerald's Electric Machinery. It's a standard textbook for the first course you would take as an undergrad in electric machinery. They go through the derivation of energy conversion starting from the law of the conservation of energy to models for different types of machines. I will leave it to you to research that yourself but here is a quote from the book (this is from a section that is introducing synchronous AC motors):Browser said:Have it your way; whilst you cannot have an electric motor without back-EMF; IT DOES NOT mean that "back-emf is fundamental to how a motor converts power".
The bold is not in the original, I added it. Then a little bit later in a section on DC machines:"In a motor the electromechanical torque is in the direction of rotation and balances the opposing torque required to drive the mechanical load. The flux produced by currents in the armature of a synchronous motor rotates ahead of that produced by the field, thus pulling on the field (and hence on the rotor) and doing work. This is the opposite of the situation in a synchronous generator, where the field does work as its flux pulls on that of the armature, which is lagging behind. In both generators and motors, an electromechanical torque and a rotational voltage are produced. These are the essential phenomena for electromechanical energy conversion."
"Thus, just as in the ac machines discussed previously, it is the interaction of these two flux distributions that creates the torque of the dc machine. If the machine is acting as a generator, this torque opposes rotation. If it is acting as a motor, the electromechanical torque acts in the direction of the rotation. Remarks similar to those already made concerning the roles played by the generated voltage and electromechanical torque in the energy conversion process in synchronous machines apply equally well to dc machines."
In addition to its utility in motor analysis, (3.43) has profound implications in motor design. According to (3.43), for a given mechanical output power, the required electrical input power can be composed of a high back EMF at a low current, a high current at a low back EMF, or some compromise in between. Of these choices, a high back EMF at a low current is preferred, because it minimizes the current handling requirements of the power electronics used to drive the motor.
"Based on a simple example, conservation of energy was used to show that force or torque is related to the power absorbed by the back EMF of a winding. This relationship provides a simple and important connection between back EMF and torque, which is valuable in motor design. "
This seems to be a limitation of the terminology... Obviously, the frequency component is significant in the "copper losses" of the kind of air cored motor you're proposing. For an iron cored motor, these kind of losses would, overwhelmingly, occur in the core and would be called iron losses. This kind of confusion is why I prefer the term parasitic losses.Browser said:Punx0r said:Woah... Copper losses are proportional only to current (at a given temperature)...
You think there is no frequency component whatsoever in copper losses? Right.
You've never let "fundamental laws of physics" get in your way They don't come more fundamental than the first law of thermodynamics....Browser said:Hah. It's a fundamental law of physics; but you think it "doesn't apply".
learningrc said:Then at the end of the chapter summary, he writes:
"Based on a simple example, conservation of energy was used to show that force or torque is related to the power absorbed by the back EMF of a winding. This relationship provides a simple and important connection between back EMF and torque, which is valuable in motor design. "
Miles said:You've never let "fundamental laws of physics" get in your way They don't come more fundamental than the first law of thermodynamics....Browser said:Hah. It's a fundamental law of physics; but you think it "doesn't apply".
The problem that you appear to have with learning, Buk, is that you're not prepared to devote a single neuron to understanding what people are trying to communicate. Everything has to be on your terms. Has it been you against the world since you were a child?
These aren't arguments ... all I did here was quote from some texts, hoping you'd take it on their authority since you've ignored everything else I've said so far. Apparently not.Browser said:First. learningrc. THANK YOU. Thank you for formulating an actual argument rather than a knee-jerk reaction. And especially thank you for citing some actual text. (Unfortunately, you still ain't gonna like what I'm going to say )
Please re-read this phrase, in a dispassionate and analytical way: "force or torque is related to the power absorbed by the back EMF of a winding." because that would appear to be the foundation of this (apparently widespread, though I've never encountered it anywhere else than here) misunderstanding.
And the key to that misunderstanding are the two words "power absorbed". You, and many others appear to think that sentence implies that that "absorption of power" is a good thing. That some how "power absorbed by back-EMF" means that power is made available to do work.
Now read my slightly modified version of that sentence: <i>"force or torque is negatively related to the power absorbed by the back EMF of a winding.".
Or to paraphrase: the more power absorbed by back-EMF; the less torque is available to do work.
As for your EI = Tw. The problem is that you insist on saying that E is back-EMF; but E in that equation is EMF. Ie. the applied voltage from the batteries.
If E were back-EMF, then that would mean that the energy from the batteries doesn't appear in that equation at all. And if you could create torque with no power from the batteries, then you'd have a free energy machine.
I can only conclude that this is either some kind of elaborate hoax -- hazing the outsider -- or some kind of mass delusion, because it is all right there in the quotes you cite; but you'll just don't seem to be able to see it.
Browser said:As for your EI = Tw. The problem is that you insist on saying that E is back-EMF; but E in that equation is EMF. Ie. the applied voltage from the batteries.
If E were back-EMF, then that would mean that the energy from the batteries doesn't appear in that equation at all.
Lebowski said:Browser said:As for your EI = Tw. The problem is that you insist on saying that E is back-EMF; but E in that equation is EMF. Ie. the applied voltage from the batteries.
If E were back-EMF, then that would mean that the energy from the batteries doesn't appear in that equation at all.
E is the back-emf voltage, not the energy. And the battery voltage does not appear in that equation because it does not play a role.
The battery will supply (more than) EI amount of energy but the battery voltage and current are unrelated to E and I and can be totally different.
But the product of the battery voltage and current will be higher than EI.
Operating Equilibrium Under Load
The "Action and Reaction" effects outlined above provide an important automatic self regulating feedback mechanism in both DC and AC motors for adapting to changes to the applied load. As the load on the motor is increased it tends to slow down, reducing the back EMF. This in turn allows more current to flow generating more torque to accommodate the increased load until a point of balance or equilibrium is reached. Thus the motor will set itself to an appropriate speed for the torque demanded.
"According to fundamental laws of nature, no energy conversion is possible until there is something to oppose the conversion. In case of generators this opposition is provided by magnetic drag, but in case of dc motors there is back emf."
Laws of Nature are to be distinguished both from Scientific Laws and from Natural Laws. Neither Natural Laws, as invoked in legal or ethical theories, nor Scientific Laws, which some researchers consider to be scientists' attempts to state or approximate the Laws of Nature, will be discussed in this article. Instead, it explores issues in contemporary metaphysics.
Within metaphysics, there are two competing theories of Laws of Nature....
Browser said:(But, it won't be due to back-EMF producing torque!)
major said:I have never said nor have I seen another say on this thread that induced voltage is responsible for the motor turning.
major said:Please indicate what you are talking about with direct quotes.
learningrc said:.... Kingsley and Fitzgerald's Electric Machinery. It's a standard textbook for the first course you would take as an undergrad in electric machinery.
.... the roles played by the generated voltage... "
major said:Who has said that back-EMF produces torque?
Browser said:Because that is the logical consequence of the statements you are making.major said:Who has said that back-EMF produces torque?
major said:Browser said:Because that is the logical consequence of the statements you are making.major said:Who has said that back-EMF produces torque?
No, it is not.
lebowski said:Torque can be produced without backemf but at standstill only, and in that case the torque does not do any work (no power is delivered)
Browser said:(But, it won't be due to back-EMF producing torque!)
major said:Who has said that back-EMF produces torque?
Browser said:major said:Browser said:Because that is the logical consequence of the statements you are making.
No, it is not.
Yes. It is.
major said:The developed torque (Tem) = Kt * Φ * Ia where Ia is armature current.
Browser said:You may not be saying it; or concluding it, but others are:
lebowski said:Torque can be produced without backemf but at standstill only, and in that case the torque does not do any work (no power is delivered)
major said:lebowski said:Torque can be produced without backemf but at standstill only, and in that case the torque does not do any work (no power is delivered)
He says "without". Torque is NOT caused by back-EMF.
Browser said:major said:lebowski said:Torque can be produced without backemf but at standstill only, and in that case the torque does not do any work (no power is delivered)
He says "without". Torque is NOT caused by back-EMF.
He said (with added emphasis): "Torque *can* be produced without backemf *but at standstill only,*"
Thereby implying "torque cannot be produced without back emf" except at standstill".
Which of itself is a perfectly reasonable statement; but it implies that back-EMF is *required* to produce torque.
Lebowski said:the torque does not do any work
major said:No. Your logic is flawed. Back-EMF is not *required* to produce torque; it is a consequence of the motion. That motion may occur as a result of the torque.