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Why it must be T²/P and NOT T/√P or T/P: Argumentation for motor constant Km = T²/P
This motor constant shall be expressed by the SI Units N²m²/W, since resistive power loss "P" is not dependent on current (or torque) linearly, but quadratically.
P = I²R (resistive loss)
Torque "T" and armature current "I" are proportional to each other. This is expressed by the Torque constant Kt. Back EMF Force (or Voltage) constant "Ke" in [Vs/rad] or Torque constant "Kt" in [Nm/A], as it is both the same.
T= Kt * I
Some manufactures specify the motor torque constant as Nm/√W. But this is wrong, too as i can show you by a little example. Imagine a machine that has a Ke = Kt of 1 Nm/A and a terminal resistance "R" of 1 Ω. At 1Nm it pulls an armature current of 1A. It’s resistave power loss is I²R=(1A)² x 1 Ω = 1W. At 10Nm it is 100W as it pulls 100A armature current respectively.
A motor that is double the armature stack oft the above one, would have a Kt of 2, as Back EMF would be doubled and resistance would be doubled, too, as conductor length was doubled. So the resistance of this machine is 2 Ω. Everything is double the motor oft he first one. So we should expect a Km figure that is double the Km figure of he first machine. By definition Km =T²/P=Kt²/R = 2²/2= 2 this is the case. With the other definitions if have seen, this is not the case. For example Kt/R = 2/2 which equals one. Makes absolutely no sense. Or Kt/√R = 2/√2 which equals 1.41. Better, but still not near a figure of 2.
Hi, I'm no expert but this article seems to have a lot of original research and is generally poorly written. I even think some of the information is outright wrong (like the kv-kt calculations). Would appreciate input from veteran Wikipedians Leav ( talk) 10:22, 21 June 2017 (UTC)
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The unit conversion table claims to provide conversions from one to another common SI units, but the converted to references don't exist. It frankly makes no sense either, it references Km from these sources and Km cannot be derived from most or all of them alone. Seancf ( talk) 16:53, 11 October 2023 (UTC)
![]() | This article has not yet been rated on Wikipedia's content assessment scale. |
![]() | Motor constants received a peer review by Wikipedia editors, which is now archived. It may contain ideas you can use to improve this article. |
Why it must be T²/P and NOT T/√P or T/P: Argumentation for motor constant Km = T²/P
This motor constant shall be expressed by the SI Units N²m²/W, since resistive power loss "P" is not dependent on current (or torque) linearly, but quadratically.
P = I²R (resistive loss)
Torque "T" and armature current "I" are proportional to each other. This is expressed by the Torque constant Kt. Back EMF Force (or Voltage) constant "Ke" in [Vs/rad] or Torque constant "Kt" in [Nm/A], as it is both the same.
T= Kt * I
Some manufactures specify the motor torque constant as Nm/√W. But this is wrong, too as i can show you by a little example. Imagine a machine that has a Ke = Kt of 1 Nm/A and a terminal resistance "R" of 1 Ω. At 1Nm it pulls an armature current of 1A. It’s resistave power loss is I²R=(1A)² x 1 Ω = 1W. At 10Nm it is 100W as it pulls 100A armature current respectively.
A motor that is double the armature stack oft the above one, would have a Kt of 2, as Back EMF would be doubled and resistance would be doubled, too, as conductor length was doubled. So the resistance of this machine is 2 Ω. Everything is double the motor oft he first one. So we should expect a Km figure that is double the Km figure of he first machine. By definition Km =T²/P=Kt²/R = 2²/2= 2 this is the case. With the other definitions if have seen, this is not the case. For example Kt/R = 2/2 which equals one. Makes absolutely no sense. Or Kt/√R = 2/√2 which equals 1.41. Better, but still not near a figure of 2.
Hi, I'm no expert but this article seems to have a lot of original research and is generally poorly written. I even think some of the information is outright wrong (like the kv-kt calculations). Would appreciate input from veteran Wikipedians Leav ( talk) 10:22, 21 June 2017 (UTC)
Hello fellow Wikipedians,
I have just modified 2 external links on Motor constants. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.
This message was posted before February 2018.
After February 2018, "External links modified" talk page sections are no longer generated or monitored by InternetArchiveBot. No special action is required regarding these talk page notices, other than
regular verification using the archive tool instructions below. Editors
have permission to delete these "External links modified" talk page sections if they want to de-clutter talk pages, but see the
RfC before doing mass systematic removals. This message is updated dynamically through the template {{
source check}}
(last update: 5 June 2024).
Cheers.— InternetArchiveBot ( Report bug) 12:42, 6 February 2018 (UTC)
The unit conversion table claims to provide conversions from one to another common SI units, but the converted to references don't exist. It frankly makes no sense either, it references Km from these sources and Km cannot be derived from most or all of them alone. Seancf ( talk) 16:53, 11 October 2023 (UTC)