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.
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