learningrc
100 mW
- Joined
- Feb 27, 2015
- Messages
- 38
Browser said:Not interested in be "taught" fallacies like: "back-emf is fundamental to how a motor produces power".
A motor doesn't produce power, it converts energy from one form to another, more or less efficiently. And 'back-emf" has nothing, zip, nadda to do with that conversion process; it is the by-product of it.
You are absolutely right ... I shouldn't have written "produces." Completely wrong on my part. I hope you can see, though, that everything I wrote after that sentence referred to "converting" so I would have hoped you could tell it was just the wrong word, not some big "fallacy" or misunderstanding on my part. Kind of like how you say below that the applied voltage "passes though the coils and creates a magnetic field." I'm assuming you know that voltage is just a potential difference and it is current that passes through coils, not voltage.
'Induced voltage' is fundamental to the energy conversion; but 'induced voltage' != 'back-emf'.
For there to be "back-emf" (also termed counter-EMF), there has to be an existing EMF, for it to counter. In a generator, there is no applied voltage, the induced voltage is thus just 'EMF'. Mechanical energy converted to electrical energy by way of magnetism; no "back-emf" required.
In a motor, there is an applied voltage, the EMF. It passes through the coils and creates a magnetic field, that magnetic field interacts with another magnetic field -- the PM in PMSMs -- and that interaction causes mechanical movement. Torque in a rotating motor; just force in a linear motor. And electrical energy has been converted to mechanical energy.
However, a by-product of the movement caused by the interaction of the two magnetic fields is that the relative motion between them induces voltage back into the coils, a voltage that opposes the EMF already flowing there, thus "back-" or "counter"-emf.
EMF (supplied voltage) creates torque; converting electrical energy to mechanical energy.
(In a motor) Back-EMF (induced voltage) is a parasitic by-product of that process, that opposes that conversion and ultimately limits it.
It cannot be avoided completely; but it should be minimised wherever possible to improve efficiency.
Are these the ramblings of a troll?
Trolls are trolls because of their behavior, not because of how knowledgeable they are.
Minimizing back-emf does nothing to improve efficiency. It isn't associated with any losses at all. EI = Tw. If the left hand side of that equation is zero because E is zero, then the right hand side also has to be zero. You literally cannot have power conversion without back-emf.