[Elecraft] [K2] External Fan Hum

[David Woolley]

Most "DC" fans used for equipment cooling use what are fundamentally 
synchronous AC motors, but with the twist that the the AC frequency is 
adjusted to match the rotation rate.  (You can also consider them as 
stepper motors, operating at maximum slew rate.)

That's what "brushless DC motor really means".

I'd expect to see an AC field, although at a multiple of the rotation 
rate, and with quite small gaps between stator poles, so with the 1/3 
power near field fall off, quite weak at distances.  On the other hand, 
they will be square wave, before the inductances gets to them.

-- 
David Woolley
Owner K2 06123


On 07/11/18 14:56, Don Wilhelm wrote:
> The DC fan may have a magnetic field, but it would be constant instead 
> of alternating polarity 120 times a second.