Ceiling Fan

Robert F Jarvis

Well-Known Member
We have out a ceiling fan on set. It is thee speed but even the slow setting is too fast for the director. We can't feed it from our varactor dimmers so how do we slow it? Would a variable rheostat work?
 

RonHebbard

Well-Known Member
Premium Member
We have out a ceiling fan on set. It is thee speed but even the slow setting is too fast for the director. We can't feed it from our varactor dimmers so how do we slow it? Would a variable rheostat work?
Use the largest 70.7 volt audio amplifier you have and feed a variable frequency sine wave generator into it. Sweep the oscillator's output down to the speed your director likes (If she likes a different speed tomorrow, no problem).
Toodleoo!
Ron Hebbard
 

Robert F Jarvis

Well-Known Member
American DJ MB DMX II Mirror Ball Motor - DMX Controllable?
Ah. That is very interesting. We have regular fan assembly up now so have a commercial fan controller on way. They'll have to run it stage side fort his show. But! I'll get one of those motors and Attach fan blades for future. Can also see other DMX apps (Like a Dutch windmill etc.) Rons reply actually gets down to the physics of the fan motor which is good to know.
 

Robert F Jarvis

Well-Known Member
Ah. That is very interesting. We have regular fan assembly up now so have a commercial fan controller on way. They'll have to run it stage side fort his show. But! I'll get one of those motors and Attach fan blades for future. Can also see other DMX apps (Like a Dutch windmill etc.) Rons reply actually gets down to the physics of the fan motor which is good to know.
I got a so-called motor controller, but it must be a varactor because it - like a dimmer - didn't slow the fan down even at the lowest setting.
If I had time, I'd get that disco motor and make my own fan using the blades from this one.
Are there any electricians out there who could answer this question: Would a real (nichrome wound) rheostat feeding the fan work? Inside, the fan has highly inductive windings tapped in three places and a straddled by capacitors. Shorting the caps changes the speed so I'm not sure of LC impedance and if feeding a lower voltage, would work. They certainly do not like the chopped ac sine wave from varactors.
 

Les

Well-Known Member
"PWM'ing" the motor is an interesting idea. This could be effective and last the entire show, or it could fail spectacularly in the middle of the first performance. I would be primarily concerned about the motor capacitor and possibly overheating the starting winding in the motor, since they are only designed to be energized for a few seconds as the fan comes up to speed. These things are rarely over-designed.

Unfortunately, there is no cheap, easy way to speed-control an induction motor. This is why things that require fine speed control typically employ permanent magnet DC motors. The most effective way to control your current motor would be to use a VFD (variable frequency drive), which could be expensive.

The mirror ball motor is an interesting take. I'm looking forward to hearing how it plays out!
 
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Robert F Jarvis

Well-Known Member
VFDs, again, something to put in bench book for the future. I made a simple small round wooden platform and attached the blades to that. Put a vertical pipe/axle on it to make a lightweight fan and hung that on a DMX Disco Ball motor. Even at its fastest (who spins a disco ball?) it's very slow, exactly what they wanted. Thanks to all, I learned some good new stuff so the whole exercise was a good hack.
 

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