In reply to Terry Blanton's message of Sat, 19 Dec 2009 17:11:58 -0500: Hi, [snip] >On Sat, Dec 19, 2009 at 3:45 PM, <[email protected]> wrote: > >> You have this backwards. > >That's not unusual for me. > >> BEMF is what makes electric motors efficient. > >It's what generates torque in an AC motor.
Torque is a consequence of the current that flows. That in turn is driven by the difference between forward and backward EMF. So the greater the load, the slower the motor and the lower the BEMF. That results in a larger difference and a greater current which increases the torque, largely compensating for the larger load, and ensuring that the power supplied largely matches the power consumed. > >> Were it >> not for BEMF, they would be a dead short and consume vast amounts of power. > >You speak of impedance. Let's not forget plain old resistance. Yes "dead short" was a bit of an exaggeration. > >> It's the BEMF which keeps the losses to a small percentage of the work done. > >Steorn's motor is essentially unloaded. If he were killing BEMF on a >pulse motor (essentially a dc motor) his RPM would skyrocket. Yes, but it would always consume maximum power, and rapidly overheat. Regards, Robin van Spaandonk http://rvanspaa.freehostia.com/Project.html
