Simple fan control

[Singburi Sam]

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

 

[TuT]

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 old electro-mechanical induction watt-hour meters register only the real
component of power consumption, so domestic users are not billed for the
consequences of poor power-factor with these meters. The new electronic
power meters monitor much more than just the active power consumption,
though I'm not sure off the top of my head whether the domestic billing
policy has changed, to take account of this and charge domestic users for
the V*A product.

The following link gives more info:

http://www.st.com/stonline/press/news/back2005/p1642d.htm

 

[Noway2]

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.

 

[petrus bitbyter]

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 series inductor changes both voltage and current to the fan. A series
inductor acts like an AC-resistor, so the fan is slowed down due to the
reduced current. The overall voltage will not be changed, but voltage across
fan and inductor added will not result in the overall voltage. (So when you
measure them separately and add the results.) Conventional TL-tube ballasts
function the same way.

AFAIK power companies all over the world bill for real power. You do not use
anything else. But inductive loads cause losses in the network so the
companies claim measures to be made by their customers to reduce the so
called blind power. That's why that ballasts are often accompanied by
capacitors. Especially power users will be checked and have to pay a fine
when they cause to much blind power. Lately I've heard that some power
companies simply bill their customers for the blind power. But I can't
imagine they can claim the same rate as for real power.

petrus bitbyter

 

[[email protected]]

How big are the inductors in this "little" speed control box? It would
work that way, just as you said (introducing a delay, which is
increasing the inductive reactance) but inductors that size would
probably cost more than a simple triac phase controller.

Say it runs full speed at 1 amp (no series inductors) and medium speed
at 1/2 amp. For a 120Vac line, that 120 ohms of inductive reactance.
At 50 or 60 hz you are going to need a 300 MILLI-henry inductor, rated
for half an amp. That's going to be a couple two or three cubic inches
for each inductor, I think.

Sure there isn't a triac in there someplace? Would make a lot more
sense with the lightning knocking it out, too.