Quote:
Originally Posted by SteveU
Intrigued: By reducing the field, the armature has to spin faster to generate a back EMF that matches the input. Some big AC motors use this for speed control, but if the field supply fails the motor goes crazy. Likewise, an automotive alternator is controlled by controlling the field current.
A basic concept is that the motor current is the difference between the input voltage and back EMF divided by the coil resistance, so as the torque load increases, the motor slows down a tiny bit, reduces the back EMF and the current increases, pulling harder. So the motor speed is a function of input voltage divided by the field current. Of course, there are practical limits like the field current must not be too low.
Steve
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Whew! Got my paper turned in, and am catching up. I still actually have enough brain power to understand the most of that! I used to be an ASE Master Automotive Tech, so I can see how alternators relate, and can now understand how they can (sometimes at least) be used as a motor also.
I'm really glad to better understand the field weakening idea. It's frustrating to hear about things you don't understand... and you guys are light-years ahead of me...
