On Tue, 30 Jul 2013 09:03:48 -0600, bud--
wrote:
On 7/29/2013 9:18 PM, The Daring Dufas wrote:
On 7/29/2013 3:45 PM, passerby wrote:
replying to The Daring Dufas , passerby wrote:
the-daring-dufas wrote:
You could try a regular light dimmer.
Small AC fans usually have shaded pole motors, RPM of which is frequency
dependent. By cutting off part of the phase with a light dimmer you will
just make it start even harder than it already is for this type of a
motor. There may be *some* RPM control due to torque losses when
dimmer is
dialed down, but it's only a small percentage point around the designed
RPM, not from 0 to the max.
Since the actual complaint is noise, not RPMs per se, I would take the
fan
apart and try to balance the blades to deal with vibration. You know,
disconnect the motor from power and spin the blades by hand. Mark which
blade stops at the bottom, do it again. If the same blade stops at the
bottom again, file some material off that blade, repeat until no single
blade stops at the bottom repeatedly. Hard to say how effective it
will be
with lightweight plastic blades coupled to a badly constructed motor, but
is worth a try. Not much else to do: if you have to look at the motor,
you
might as well just get yourself a new fan - motor is the bulk of the cost
of it, anyway.
My suggestion was about a low cost experiment. I built a variable
voltage box using a triac, pot, trigger diode, capacitor, single 120
volt 15 amp outlet, cord, cord grip and sloped project box. I was able
to use it for all sorts of things including shaded pole motors, light
bulbs and universal AC/DC motors. If he uses a triac type dimmer, it
should work. A dimmer using an SCR might not work very well. The link
below is about LED dimming but shows the waveform output of a triac type
dimmer. ^_^
http://www.digikey.com/us/en/techzon...C-Dimmers.html
https://tinyurl.com/l655p55
TDD
If you use a triac dimmer control the motor torque falls off pretty
rapidly. But as you reduce the fan speed the torque required falls off
rapidly also, something like the 3rd power of the RPM. I never used a
dimmer to control a fan, but it might work. From mickey, it often does work.
I should say that every fan I have except the 4" fan (which is a year
old) is over 25 years old. I have a Tintang** (or something like
that, 2-speed fan) that is about 25 years old, but I've never used a
speed control with it, or with the 4" fan. **Co-workers gave me this
when they felt sorry for me when I was using a fan from the '30's.
But I liked the older fan more, until it caught fire last summer (fan
stopped, overheated, and set fire to too much light oil).
The rest are 30 to 80 years old. I don't think newer fans from the
last 10 years are made differently from my older ones, which are all
(except maybe one) brushless, induction motors. I guess I could try
dimmers on those two newer fans if anyone was curious.
I got the old fans, with iron or heavy steel bases, from my father
when he died in 1955 at age 62. They were in his office or our home.
I believe a triac dimmer will maintain torque better than a resistor.
The box fans I have make noise because of the air being moved, not
because of balance problems.
Yeah.