# Ceiling Fan Control **URL:** \ **Category:** Factual Questions\ **Tags:** tools-electric-diy\ **Created:** [August 16, 2024, 10:10am UTC](https://boards.straightdope.com/t/ceiling-fan-control/1005787 "2024-08-16T10:10:17Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [August 16, 2024, 10:10am UTC](https://boards.straightdope.com/t/ceiling-fan-control/1005787/1 "2024-08-16T10:10:17Z")
I have a ceiling fan in the bedroom with three speeds and a remote control. Can someone explain how the variable speed works? If it matters, the fan is on a 230V AC supply. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [August 16, 2024, 12:49pm UTC](https://boards.straightdope.com/t/ceiling-fan-control/1005787/2 "2024-08-16T12:49:10Z")
Does the 230V AC supply mean you are in England? It’s possible your fan was made with three separate power inputs for the different speeds. The switch would be a simple mechanical switch to change the inputs or disconnect all of them to turn it off. ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [August 16, 2024, 12:50pm UTC](https://boards.straightdope.com/t/ceiling-fan-control/1005787/3 "2024-08-16T12:50:59Z")
Yes, in England. How would you have different power inputs? ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [August 16, 2024, 12:56pm UTC](https://boards.straightdope.com/t/ceiling-fan-control/1005787/4 "2024-08-16T12:56:28Z")
The fan motor is wired internally to provide different voltages to the windings. I think this is done by supplying voltage to different points on a coil like a VariAC transformer, maybe called an autotransformer in your neck of the woods. I think this is how most 3 speed fans work around the world. Some can be controlled with a variable speed controller that reduces voltage in the switch itself but if not designed that way it may create a fire hazard. ---
**Author:** ![andrewm](https://avatars.discourse-cdn.com/v4/letter/a/c57346/32.png) [@andrewm](https://boards.straightdope.com/u/andrewm)\ **Post date:** [August 16, 2024, 1:26pm UTC](https://boards.straightdope.com/t/ceiling-fan-control/1005787/5 "2024-08-16T13:26:56Z")
That is **absolutely not** how household AC fan motors are speed-controlled. You’re not going to fit a variac into a light-switch size package. The typical methods are switching capacitors in series with the motor, or a triac-based circuit to control the duty cycle, similar (but not identical) to an incandescent light dimmer. Some more modern fans with built-in controllers and remotes now use brushless DC motors with a variable-frequency drive. These must stay paired with their controller and can’t be used with AC fan speed controllers. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [August 16, 2024, 1:59pm UTC](https://boards.straightdope.com/t/ceiling-fan-control/1005787/6 "2024-08-16T13:59:40Z")
> [@andrewm](#): > > You’re not going to fit a variac into a light-switch size package. Whatever method is being used to control it, it would be in the fan’s housing, not the switch. Especially in this case, given the OP is using a remote. Also, I’ve seen the word variac a million times but never noticed it’s “variable AC”. At least that’s where I’m assuming the name comes from. ---
**Author:** ![xtenkfarpl](https://avatars.discourse-cdn.com/v4/letter/x/c2a13f/32.png) [@xtenkfarpl](https://boards.straightdope.com/u/xtenkfarpl)\ **Post date:** [August 16, 2024, 2:53pm UTC](https://boards.straightdope.com/t/ceiling-fan-control/1005787/7 "2024-08-16T14:53:49Z")
> [@TriPolar](#): > > I think this is how most 3 speed fans work around the world. I don’t think so. The control is almost certainly a solid state device like a thyristor or triac, which works by adjusting the duty cycle of the power fed to the motor. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [August 16, 2024, 2:56pm UTC](https://boards.straightdope.com/t/ceiling-fan-control/1005787/8 "2024-08-16T14:56:37Z")
> [@andrewm](#): > > The typical methods are switching capacitors in series with the motor Yep. The typical design is to have two motor windings: one winding connects directly to AC, and the other winding is in series with a capacitor. Speed is changed by selecting one of three capacitors. > [@Joey\_P](#): > > Also, I’ve seen the word variac a million times but never noticed it’s “variable AC”. At least that’s where I’m assuming the name comes from. [Variac®](https://variac.com/) is also a registered trademark. ---
**Author:** ![xtenkfarpl](https://avatars.discourse-cdn.com/v4/letter/x/c2a13f/32.png) [@xtenkfarpl](https://boards.straightdope.com/u/xtenkfarpl)\ **Post date:** [August 16, 2024, 3:33pm UTC](https://boards.straightdope.com/t/ceiling-fan-control/1005787/9 "2024-08-16T15:33:37Z")
> [@Crafter\_Man](#): > > Yep. The typical design is to have two motor windings: one winding connects directly to AC, and the other winding is in series with a capacitor. Speed is changed by selecting one of three capacitors. Interesting… I’ve never taken one apart to examine it. I always thought they worked by adjusting the duty cycle with a solid state switch, which is how light dimmers work, or at least used to? Mind you, if it’s a remote control, switching between windings is still probably done with a solid-state switch, I expect. If it was an old school pull-string control it would probably be mechanical. Side note: most of the Variacs I’ve seen, in university and industrial labs, have been pretty heavy things… not something you’d fit in a fan housing… 🙂 ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [August 16, 2024, 4:04pm UTC](https://boards.straightdope.com/t/ceiling-fan-control/1005787/10 "2024-08-16T16:04:11Z")
> [@xtenkfarpl](#): > > I always thought they worked by adjusting the duty cycle with a solid state switch, which is how light dimmers work, or at least used to? This is way outside my area of knowledge, but I’m pretty sure most ceiling fans use an induction motor, and (I think) you can’t vary the speed of an induction motor using a phase-fired proportional control (e.g. a light dimmer using a triac to vary the conduction angle). But I think you can use one on a universal AC/DC motor that has brushes. ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [August 16, 2024, 4:06pm UTC](https://boards.straightdope.com/t/ceiling-fan-control/1005787/11 "2024-08-16T16:06:32Z")
Hmm… Various solutions here. The controller in the fan is pretty small. BTW - it can also be set to run in reverse, but with a switch on the casing, not the remote. I have always assumed that the fan would use more (KwH) at higher speeds. Clearly, there is more resistance at high speed, but is the higher speed intrinsically more power-hungry? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [August 16, 2024, 4:08pm UTC](https://boards.straightdope.com/t/ceiling-fan-control/1005787/12 "2024-08-16T16:08:33Z")
Of course it is. You don’t get something for nothing. ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [August 16, 2024, 4:09pm UTC](https://boards.straightdope.com/t/ceiling-fan-control/1005787/13 "2024-08-16T16:09:40Z")
But the low speed may simply waste the surplus energy as heat for example? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [August 16, 2024, 4:11pm UTC](https://boards.straightdope.com/t/ceiling-fan-control/1005787/14 "2024-08-16T16:11:53Z")
Yes, in theory. But, in practice, it’s hard to get rid of 50-100W of heat in a small enclosure, so it’s better to use a more efficient way of reducing the power consumed by the fan motor. ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [August 16, 2024, 4:12pm UTC](https://boards.straightdope.com/t/ceiling-fan-control/1005787/15 "2024-08-16T16:12:54Z")
> [@beowulff](#): > > it’s hard to get rid of 50-100W of heat in a small enclosure It does have a big fan attached…🙂 ---
**Author:** ![Snipe70e](https://avatars.discourse-cdn.com/v4/letter/s/51bf81/32.png) [@Snipe70e](https://boards.straightdope.com/u/Snipe70e)\ **Post date:** [August 16, 2024, 5:31pm UTC](https://boards.straightdope.com/t/ceiling-fan-control/1005787/16 "2024-08-16T17:31:49Z")
In the US ceiling fan speeds are controlled 2 ways. One is a switch that you pull a chain on. The motor is wired with different number of poles. There are different power leads going to a different combination of poles. from stop 1st click fan will have fewer poles and that will be high. 2nd Click and more poles fan slows down. 3rd click and even more poles fan is going slowest speed. 4th click and fan goes off. Now if you add a remote to the situation the fan should be clicked into its highest speed. Then wire in the remote control receiver between the fan switch and the power source. Connect a hot and neutral to the receiver. Now your hand held remote will change the input to the fan. There is no change in the fan wiring or set up. The remote receiver is physically remote from the fan itself. Clicking the remote will change the out put of the remote receiver. I believe the receiver will change the frequency being supplied to the fan. To me it is an electric black box so I am taking an educated guess. ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [August 16, 2024, 5:33pm UTC](https://boards.straightdope.com/t/ceiling-fan-control/1005787/17 "2024-08-16T17:33:05Z")
> [@Snipe70e](#): > > To me it is an electric black box so I am taking an educated guess. I thought this was FQs? ---
**Author:** ![xtenkfarpl](https://avatars.discourse-cdn.com/v4/letter/x/c2a13f/32.png) [@xtenkfarpl](https://boards.straightdope.com/u/xtenkfarpl)\ **Post date:** [August 16, 2024, 5:36pm UTC](https://boards.straightdope.com/t/ceiling-fan-control/1005787/18 "2024-08-16T17:36:40Z")
> [@Crafter\_Man](#): > > This is way outside my area of knowledge, but I’m pretty sure most ceiling fans use an induction motor, and (I think) you can’t vary the speed of an induction motor using a phase-fired proportional control (e.g. a light dimmer using a triac to vary the conduction angle). But I think you can use one on a universal AC/DC motor that has brushes. There may be different approaches… in the past a mechanical switch might have been used to turn separate windings on or off selectively? Newer devices almost certainly use solid-state switching? I guess the only way to check is to disassemble one and trace the circuitry. But bob-2 probably doesn’t want to hack up his fan for scientific curiousity… 🙂 ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [August 16, 2024, 8:19pm UTC](https://boards.straightdope.com/t/ceiling-fan-control/1005787/19 "2024-08-16T20:19:07Z")
I recently replaced a fan speed controller module that I previously installed and had stopped working. I took it apart but wasn’t able to diagnose the fault. For one, it uses just two conductors that go to the fan. It doesn’t switch the windings on and off. A similar module says “capacitive-type fan speed control”, and indeed the module itself has four beefy capacitors. The specs also say “zero cross switch technology”. So I believe the module connects varying numbers of capacitors during the AC zero crossing. This is just the method that **Crafter\_Man** mentioned, but done electronically. I believe this has the effect of altering the phase of the fan voltage/current, which affects the amount of torque (and thus the fan speed). ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [August 16, 2024, 8:52pm UTC](https://boards.straightdope.com/t/ceiling-fan-control/1005787/20 "2024-08-16T20:52:22Z")
I managed to find a pretty comprehensive study on ceiling fans - [CBE-Ceiling-Fan-Design-Guide-V0.pdf (berkeley.edu)](https://cbe.berkeley.edu/wp-content/uploads/2020/04/CBE-Ceiling-Fan-Design-Guide-V0.pdf) > The power consumed by a fan increases in proportion to the cube of its rotational speed, while the > airflow generated by the fan increases linearly with its rotational speed. Thus, fan efficacy - or the airflow > per unit power consumed - decreases as fan speed increases. However, in many fan models, motor > efficiency is poor at lower speeds, partially counteracting this effect. In the MAEDbS dataset, the typical > (median) fan efficacy at the lowest operating speed of each fan is 165 cfm/W, while it is 79 cfm/W at > highest operating speed. > There are three main types of motors used in ceiling fans: AC Induction, Permanent Magnet DC (PMDC), > and Brushless Direct Current (DC) motors. Generally, there are very large percentage efficiency savings > from moving from AC to DC motors for small fans, and far less of an effect for large diameter fans. > • AC Induction: > o How it works: Electromagnets on outside of motors (stator) creates a rotating magnetic field > causing motor rotation through induction. > o Benefits: Provides constant, even airflow and are cheaper than DC motors. > • PMDC: > o How it works: Permanent magnets are located on the motor stator creating a stationary magnetic > field. A segmented commutator rotates within the magnetic field creating a mechanical switching > of current direction. > o Benefits: More energy efficient than AC motors and provides constant force over a wider range of > speeds than AC motors. > • Brushless DC: > o How it works: Permanent magnets are rotated in motor creating a rotating magnetic field. Current > direction in the stator is switched in relation to the magnetic field to create rotation. > o Benefits: Most energy efficient of the three motor types (for small motors on small diameter fans, > a DC motor often will use 70% less energy than an AC motor), most quiet, and has a longer service > life than PMDC motors. I am guessing that the fan in my bedroom is a Brushless DC type. [Next page](https://boards.straightdope.com/t/ceiling-fan-control/1005787.md?page=2)