BLDC vs AC motor

BLDC vs AC motor

Postby Golear » Thu May 21, 2020 2:41 pm

So... this might be a dumb question, but what is the operational difference between a BLDC motor and an AC motor?

I'm asking about operational difference, not difference in parts. And this has nothing to do with Vienna Acoustic's project, or Bill/Phoenix Engineering, or SOTA, or VPI. I'm asking from a purely technical point of view.

As far as I can tell, they both have coils, and they both receive a sine wave signal. The signal is a single sine wave when it comes to an AC motor, and is a set of sine waves when it comes to a BLDC (the number of waves depending on the number of magnets). But after that, both create a rotating magnetic field and so the stator and rotor should behave in an identical way, right? Is there a difference in the magnetic fields?

(And what about AC motors that are fed non-sine wave signals? These only turn the stator "on" when the rotor's poles are between the stator's poles. So they give a softer kick to the rotor. This would, of course, be very inefficient for a train motor, but might result in less vibration for a turntable motor. In this case, there IS a fundamental difference in the magnetic field.)

Anyone know what kind of motors are used on the gyroscopes on the Hubble Telescope? I think that's the ultimate requirement for turning something with minimal vibration.

Thanks
Golear
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Re: BLDC vs AC motor

Postby theeng » Thu May 21, 2020 5:13 pm

Golear,

This site has a simple table that compares the two designs at a top level view - https://www.completepowerelectronics.co ... on-motor/,.

Beyond the above, there is a wealth of info available on the web, just search BLDC vs AC Motor. But, the above hits the top items, and the flat-torque curve and lower in-rush current are big items.

Neil
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Re: BLDC vs AC motor

Postby Golear » Thu May 21, 2020 7:11 pm

That was very helpful. Thanks.
Golear
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