OT- Light dimmer to vari fan speed?

dkmc · Dec 6, 2014

Can a Light dimmer be used to control the speed of a typical 12" table fan
that has (I suspect) a synchronous motor?
Fan has 3 speeds already, but slow is too fast.

SteveM · Dec 6, 2014

I just saw this at Home Depot today:

Lutron Maestro 1 Amp Single-Pole 7 Speed Combination Fan and Light Control - White-MA-LFQHW-WH at The Home Depot

Looks like you install a module in the fan, and then you can control the fan and the lights separately from the control without having to run separate wires for the fan and light.

Steve

dkmc · Dec 6, 2014

Yikes..$58....I'm wonderin if an $8 lamp dimmer would do the job

SteveM · Dec 6, 2014

dkmc said:
Yikes..$58....I'm wonderin if an $8 lamp dimmer would do the job

My guess is no, but in my case, $58 is probably less than it would cost to have an electrician run a separate wire for the fan and the light.

Steve

Racer Al · Dec 7, 2014

Two suggestions: 1) take apart the fan and look at how the speed is controlled: if the switch has resistors for different speeds, you could add resistance to the lowest speed and that should slow it down. 2) look at woodworking router speed controllers.

18my · Dec 7, 2014

No they can't. They work differently. Forgot exactly why it is, essentially they work opposite to each other. I looked into it ages ago but can't remember the exact explanation

Lakeside53 · Dec 7, 2014

If the table fan has a typical squirrel cage motor, a "light dimmer" will work. The only difference between a cheap light dimmer and cheap fan speed controller (like for a fireplace, NOT the slow speed overhead paddle fan type) is that the fan controller has an internal limit (often adjustable) to stop you going too slow (where the motor will stall).

Spend $10 and try it.

Thomas Paine · Dec 7, 2014

Regular light dimmers are Triacs, that chop the 120V waveform (SCRs), and that is what dims the light. A light is a resistive load, so this works. This is why regular dimmers don't work on flourescents.

A fan speed controller is an resistor-capacitor (RC) circuit that attenuates the waveform to lower the RMS output voltage. A motor is an inductive load.

So if you use a light dimmer, you'll eventually burn up the motor and/or get poor performance. Your insurance company might not like it either.

Someone speak up if this is incorrect.

VERSUS:

dkmc · Dec 7, 2014

I was not aware that Fan Speed Controllers existed.
I will get one of those.
Thanks!

TDegenhart · Dec 7, 2014

Thomas Paine said:
Regular light dimmers are Triacs, that chop the 120V waveform (SCRs), and that is what dims the light. A light is a resistive load, so this works. This is why regular dimmers don't work on flourescents.

A fan speed controller is an resistor-capacitor (RC) circuit that attenuates the waveform to lower the RMS output voltage. A motor is an inductive load.

So if you use a light dimmer, you'll eventually burn up the motor and/or get poor performance. Your insurance company might not like it either.

Someone speak up if this is incorrect.

VERSUS:

Not bad. Three up, three down. Triac type dimmers don't work on standard florescents because the control (ballast) is a constant current controller. I have never seen a R-C network used for a motor speed controller. You might use a capacitor to reduce the motor speed, but it would not be variable without being a step switch with a bank f capacitors. Lastly, you are right in that simply adding a speed control to a motor without consideration of the type of motor may lead to a burned up motor. Specifically, a single phase motor using a start switch will maintain the start windings on if voltage is set too low.

Tom

Lakeside53 · Dec 7, 2014

Two types of cheap fan speed controllers -switched RCL networks typically used for the overhead over head paddle types, and the "light dimmer like" triac control" used for most other small fractional hp NON-capacitor start motors. Small fan motors do not have start winding.

The TRIAC types will work fine work fine for the OP use - the motor speed is somewhat proportional to the average voltage which decreases the later the triac fires. There are milions of triac fan speed controllers in use... and they are UL listed for that purpose.

Like this : http://www.amazon.com/KB-Electronic...7997771&sr=8-11&keywords=fan+speed+controller and this http://www.amazon.com/Speed-Control...7998245&sr=8-29&keywords=fan+speed+controller

You can get this type for as little a $8.

dkmc · Dec 7, 2014

Thank you!

Lakeside53 said:
Two types of cheap fan speed controllers -switched RCL networks typically used for the overhead over head paddle types, and the "light dimmer like" triac control" used for most other small fractional hp NON-capacitor start motors. Small fan motors do not have start winding.

The TRIAC types will work fine work fine for the OP use - the motor speed is somewhat proportional to the average voltage which decreases the later the triac fires. There are milions of triac fan speed controllers in use... and they are UL listed for that purpose.

Like this : http://www.amazon.com/KB-Electronic...7997771&sr=8-11&keywords=fan+speed+controller and this http://www.amazon.com/Speed-Control...7998245&sr=8-29&keywords=fan+speed+controller

You can get this type for as little a $8.

JST · Dec 7, 2014

Most small table fans are shaded pole, dimmers work with them.

Larger fans MAY BE single unswitched capacitor ("PSC") motors, and dimmers will work with them

But any fan run by a "split phase" or cap start motor will NOT be good with a dimmer.

Spyderedge · Dec 7, 2014

Racer Al said:
2) look at woodworking router speed controllers.

Woodworking variable speed controllers are nothing more than a variable transformer.

https://www.youtube.com/watch?v=m2oyVvkvBiQ&list=UUckETVOT59aYw80B36aP9vw

OP - A light dimmer will be fine. Every ceiling fan I have ever seen that has a speed controller is nothing more then a light dimmer. I'm sure there is some argument as to the different motor types, etc. But it's a little fan, not lawnmower bearings crushed in a chuck

Most small fans I've seen are run with shaded pole induction motors, running 3250 RPM. They are dimmed with voltage control.

kd1yt · Dec 7, 2014

Spyderedge said:
Woodworking variable speed controllers are nothing more than a variable transformer.

https://www.youtube.com/watch?v=m2oyVvkvBiQ&list=UUckETVOT59aYw80B36aP9vw

OP - A light dimmer will be fine. Every ceiling fan I have ever seen that has a speed controller is nothing more then a light dimmer. I'm sure there is some argument as to the different motor types, etc. But it's a little fan, not lawnmower bearings crushed in a chuck

Most small fans I've seen are run with shaded pole induction motors, running 3250 RPM. They are dimmed with voltage control.

Respectfully but firmly differ on the assertion of "variable transformer"- if you've ever carried (they are hefty in size and weight) or priced a "variac" (true variable transformer) capable of any current capacity, you will understand that modern speed controls are different from variable transformers. Both do certain jobs well, but they are cut out for different jobs.

Spyderedge · Dec 7, 2014

kd1yt said:
Respectfully but firmly differ on the assertion of "variable transformer"- if you've ever carried (they are hefty in size and weight) or priced a "variac" (true variable transformer) capable of any current capacity, you will understand that modern speed controls are different from variable transformers. Both do certain jobs well, but they are cut out for different jobs.

Thank you for the info.
Pardon my ignorance, but what is the difference between a true variac, and a router speed control? Is a router speed control just a variable pot? I was under the assumption that a router speed control was just a small variable transformer.

JST · Dec 7, 2014

Spyderedge said:
Thank you for the info.
Pardon my ignorance, but what is the difference between a true variac, and a router speed control? Is a router speed control just a variable pot? I was under the assumption that a router speed control was just a small variable transformer.

Router control generally is basically a light dimmer, with a few mods to make operation with inductive loads more reliable. Small, usually pretty light.

A variac is a toroidal transformer with a sliding contact to vary the voltage. Big and heavy, in proportion to power level.

dkmc · Dec 8, 2014

Spyderedge said:
Most small fans I've seen are run with shaded pole induction motors, running 3250 RPM. They are dimmed with voltage control.

Wait.....I'm trying to slow the fan down, not dim the motor.....

Big B · Dec 8, 2014

My dad used a dimmer switch to slow down a fan motor that drew warm air from a greenhouse that was attached to his house. It was on there for probably 20 years and worked fine.

I have heard that using a dimmer switch also reduces the torque of the motor but with a fan that doesn't seem like much of a problem.

Big B

Spyderedge · Dec 8, 2014

dkmc said:
Wait.....I'm trying to slow the fan down, not dim the motor.....

LOL I was thinking of light dimmers when posting that. Oops!

OT- Light dimmer to vari fan speed?

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