I wouldn't worry about it much - my experience is that these cheap
crappy 12 VDC fans croak after not much use. 1st the sleeve bearing
squeal and scream, then the brushes burn the commutator and then they
won't start when cold - but all the while they make loads of RF noise.

Get a ballbearing AC fan - computer muffin fan.


On Sat, 20 Sep 2003 13:52:06 -0700, "Ed Price"
wrote:


"Steve" wrote in message
...
I purchased and intalled a nice 12 volt fan over my galley stove to
disperse
the heat build up in the overhead.

I now find that the fan motor creates a buzzing sound in my FM radio
(haven't checked yet to see if it bothers the VHF).

I'll admit, I didn't pay much ($20) for the fan at West Marine, but it is
exactly what I wanted. 12 volt, .75 amps. and it osolates.

I guess I got what I paid for..

Isn't there someway to put a filter cap. in the line to eliminate this RF
noise??

Also, it's turning at about 1200 rpm and I'm also thinking a speed control
might be useful since it kinda sends the port hole curtains a-flying. (Ok,
so it's not exactly what I wanted, in retrospect).

recommendations??


Steve
s/v Good Intentions



If the speed control is a simple rheostat, then at least that isn't the
cause of the noise. (It may waste power, but at least it isn't noisy.) OTOH,
if the speed control is electronic (controlling fan speed by chopping the
fan power; i.e., pulse width modulation), then the noise could be from the
controller and/or the motor brushes.

First, try to suppress the motor brushes. Try a capacitor, typically a 0.01
uF ceramic, across the DC power lines before they exit the motor housing
(hope the housing is metal!). Next step would be to try the capacitor just
before the power controller. Ferrite beads on the DC lines won't help much
at 100 MHz, but you can try them. Next step is to try to get some series
inductance in the DC lines, typically, try a dozen turns or so on some
ferrite or powdered iron toroidal cores.

Beyond that, a new fan might be easier than further suppression work. Try to
buy CE compliant equipment, if available.

Ed