Brushless DC without permanent magnets

Electric Motors and Controllers
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inh   1 mW

1 mW
Posts: 11
Joined: Jun 22 2012 2:30am

Brushless DC without permanent magnets

Post by inh » Jul 02 2013 12:07am

I was reading a tesla motors blog post about brushless DC versus induction motors ( ... ess-motors) and remembered that the powerplants I use at work have a somewhat similar setup to the AC induction motors. Granted, they are high voltage AC alternators used for generating electricity, but really it's just a motor being spun instead of doing the spinning...

Anyways, the way the alternators at work (Caterpillar SR4B) operate is they have the field on the rotor, and the output power comes out of the stator. The field is created by inducing a current on special windings on the rotor that are connected to the field windings. This allows the field strength to be varied, but without using brushes to transmit the power to the rotor. Hope this makes sense..

The blog post mentions that one advantage induction motors have over BLDC is that the field strength is adjustable which allows for an increase in efficiency.

Has anyone seen motor designs that do this, or something similar?

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circuit   100 kW

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Re: Brushless DC without permanent magnets

Post by circuit » Jul 02 2013 5:10am

It's how car alternators work. At least old BOSCH ones, wound in 1987 Audi.
These have two brushes with rings on the rotor and rectifier on stator. I don't see why it couldn't be used as a motor. One reason may be the thickness of stator lamination... But still would be interesting to see someone pull it off and do some graphs. I love graphs :)
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