Re: Simple fan control
- From: "Noway2" <no_spam_me2@xxxxxxxxxxx>
- Date: 19 Sep 2006 05:55:49 -0700
Singburi Sam wrote:
I know just enough about electricity to ask stupid questions.
This seems like a very friendly group, so let me try.
I bought a simple, cheap ceiling fan here in SE Asia;
it has a speed control unit (Off-1-2-3). The speed
control has four external wires: two to fan, two to
house electricity (phase and neutral).
After a lightning strike, fan had maximum speed (3)
when minimum speed (1) was selected! I replaced
the little speed control box; problem solved.
I'd wondered how such a speed control worked, and
got my chance to find out when replacing it -- I could
see the circuit, as well as a written diagram. It
was very simple: Inductors were placed in series at
lower speeds. (There was also a high-valued resistor.)
I decided (wrongly?) that the inductors, in effect,
delayed the current wave-form, so that at low-speed
the fan was still getting the same volts and amperes
as before, but fewer watts because of phase difference.
Does this make sense?
I did Google searches like "fan variable power inductor"
and saw many ways to slow down a fan, but none
of them seemed to be this way. (They spoke of $40
solutions, much more expensive than mine.)
The little puzzle got me thinking and Googling.
I learned how "watt" and "volt-ampere" have
different definitions. I guess the power company
consumes watts but bills me for volt-amperes
because they're easier to measure. The fans
don't cost much to run, but I guess I'm billed
at a higher rate (volt-amperes) than I actually
consume (watts), right? If other appliances run
concurrently, perhaps that would somehow
"average" the current phase and minimize
volt-amperes wasted???
I'm afraid I suffer from serious misconceptions
and this whole post will seem silly....
Sam
The inductors have a frequency dependant impedance associated with
them, which is calculatable from the formula Impedance (Z) =
2*pi*Freq*L. Consequently, the inductors can be used as part of a
voltage divider circuit to reduce the voltage applied to the motor and
hence reduce the speed. One of the advantages of the inductors is that
they don't have the power or rather heat dissipation like a resistor
would as the engergy is stored in the magentic field and released.
Real inductors, do have a certain amount of resistance and this does
have loss associated with it, though it is less than a resistor of
comparable impedance.
.
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