On Jul 4, 4:28*am, wrote:
On Tue, 03 Jul 2012 12:18:41 -0400, jeff_wisnia
wrote:
wrote:
I have a small window fan in my workshop. *It's one of those old metal
expandable units that fits any width of window by moving the sides. *The
fan blade is only about 9 or 10 inches. *The motor is a shaded pole
motor, similar to the motors used in the old record turntables. *But
this fan sings. *It stays at a constant speed, but the tone varies. *It
can be heard 300 feet away. *It's not a grinding sound and the blade is
not rubbing the housing. *It's just purrs along, while changing in
pitch. *Sometimes it's pretty constant, then suddenly the sound will go
up and down rapidly for a half minute or so. *At first it was sort of
annoying, but after awhile I have grown to like the sound. *Its sort of
soothing and varies like the waves on a lake.
However, just because it's a perfect fit for the small window in that
shed, I decided to take it apart and make sure it was oiled. *The
bearings are all pretty tight. *I oiled it's bearings well and
reassembled it. *I was surprised that it was much quieter for the first
ten minutes. *Then it went back to singing.
Just curious if anyone knows why it makes these sounds?
Could the pitch be changing because of varying wind pressure against the
window the fan is mounted in.
That was actually my first thoughts. *However, we have had days of calm
wind free weather. *It does not seem to indicate that the wind (or lack
of it) has any effect. *For the heck of it, I placed another fan on the
work bench in there and blew that fan toward the noisy one. *There was
little noticable change. *However, I found that there is a certain
amound of back and forth play in the motor. *What I mean, is that the
fan blade can be moved forward (away from the motor, or backward (toward
it). *This play is very small, but it exists. *What causes this is
beyond me, but I suspect that there may have been a fiber washer in
there when it was new, and that wore out. *This play is not visible when
it's spinning, but I suspect that the in and out movement of the shaft
is causing the different pitch. *Putting a shim in it might be possible..
I'll have to check what is available. *Yet it seems to me that this type
of motor always had a little play. *After all, if they are too tight,
they would drag and overheat. *After all, this is a fractional HP motor..
My guess would be 1/20 HP at most. *No, there are no capacitors. *Like I
said, this is about the same as the old record player motors. *Basically
a laminated iron housing with coils and the rotating magnets in the
middle connected to the shaft. *(similar to this).http://www.cprmotor.com/products_img...motor_yj58.jpg
Ignore the play in the shaft.
All fans will have back and forth movement of the blade. I just
checked 4 different fans:
A floor standing model, 2 dual blade window fans from different
manufacturers and an rather old "industrial" style fan from back in
the 60's.
Something like this:
http://i68.photobucket.com/albums/i1...sstuff6861.jpg
Each and every one of them has a small amount of back and forth
movement of the shaft.