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#127932 - 03/21/02 01:40 AM fan speed control  
aldav53  Offline
Joined: Aug 2001
Posts: 545
Chandler, AZ USA
A customer ask about there ceiling fans not working correctly, only one speed sometimes. It sounded like someone installed a standard dimmer, not a fan speed control. They also have a remote control not working right either. I'm sure this wouldn't be good for a fan or the dimmer itself. Light dimmers vary the voltage, not sure about fan speed controls, maybe they vary the frequency or the cycles. ??

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#127933 - 03/21/02 10:30 PM Re: fan speed control  
circuit man  Offline
Joined: Nov 2001
Posts: 273
well im not really sure about the 2 but no a dimmer & a fan speed control are 2 different creatures. [Linked Image]

#127934 - 03/28/02 11:15 PM Re: fan speed control  
Ron  Offline
Joined: Mar 2002
Posts: 582
White Plains, NY
What is the operational differences between a fan speed control and a dimmer, assuming they both have a similar wattage rating. Don't they both shunt the power through a resistor (old style dimmer)?


#127935 - 03/28/02 11:38 PM Re: fan speed control  
spkjpr  Offline
Joined: Dec 2000
Posts: 218
Sedalia,MO, USA
Ron, the newer fan controls use an SCR to chop the AC line I believe. Much like a VFD drive in a commercial application. Several of the ceiling fans I have seen warn about using a rheostat for speed control, as in don't. Some of the speed controls also appear to be transistorized.
(Man these 20 hr days are killing me. I don't type well in the first place)

[This message has been edited by spkjpr (edited 03-28-2002).]

#127936 - 04/03/02 09:53 PM Re: fan speed control  
daniel damon  Offline
Joined: Jan 2002
Posts: 31
Ambler,PA, USA

can you explain a little more. what are SCR and VFD. tring to learn as much as i can. thanks


#127937 - 04/03/02 10:58 PM Re: fan speed control  
spkjpr  Offline
Joined: Dec 2000
Posts: 218
Sedalia,MO, USA
Daniel, an SCR is a Silicon Controlled Rectifier, a diode that has a Gate used to turn it on so it will conduct. It is used in many industrial and other circuits to control how long the sine wave is on. Were I work we use them to control spot welders so we can control how much heat we apply to the metal. A VFD is a Variable Frequency Drive. Used an motors to control the speed, once again we use them at work to control the speed of a straightner, used to flatten the metal as it comes off a giant coil,so it will match the speed of the stamping press. Any time you have a question, jump in and ask. All of us here are more than willing to help, I even found a man here who answered my question about a crane control when I couldn't find any info about it. Good luck and remember as a n instructor once told me" a thirst for knowledge is a good thing, it means you are still alive!"

#127938 - 04/04/02 08:53 PM Re: fan speed control  
daniel damon  Offline
Joined: Jan 2002
Posts: 31
Ambler,PA, USA

thanks for all that info. you the man!!

#127939 - 04/04/02 10:07 PM Re: fan speed control  
Scott35  Offline

Broom Pusher and
Joined: Oct 2000
Posts: 2,708
Anaheim, CA. USA
Just some FYI stuff:

Many Dimmers and speed controls use Triacs [like 2 SCRs facing both directions] as the AC Amplifying / Controlling device.

Some fire a Diac for Gate conduction, some drive a SCS to amp the Triac's Gate.

The Speed control which is intregal with the typical Ceiling Fan Permanent Split Capacitor Motor ["PSC"] is comprised of a Tapped Autotransformer section that is wound with the Stator Winding [Primary], and is connected ahead of the Run Winding.
This is a simple method for speed control of an AC Induction Motor which limits the available KVA to the Rotor [Secondary] and the overall True Power [Wattage]. By reducing the Voltage, the Motor will reduce it's Rotor speed until it can draw enough True Power to drive the Rotor [simply reduced the cubic feet per minute of air moved].

I should have a schematic of the PSC Motor posted in the Reference section if anyone needs a visual reference.
Let me know if one is needed.

Normally, speed of AC Motors is determined by the Frequency applied to the Rotor [higher Frequency = higher speed].
A 2 Pole AC Induction Motor driven at 60 Hz will have an unloaded speed of 3600 RPMs, and slip down to around 3450 at full load.
A 4 Pole AC Induction Motor driven at 60 Hz will be 1800 unloaded / 1725 full load.
Double the Frequency and the speed doubles.
The 4 Pole motor effectivly cuts the Frequency Induced to the Secondary [Rotor] in 1/2, or Induces AC at 30 Hz to the Secondary.

Scott SET

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