Dimmer question

D

dus10

Well-known member
I am looking to control the speed of a fan, thinking a dimmer may do the trick. I have a small, 3 speed oscillating tabletop fan that I am trying to convert into a rotating tabletop display. I thought if I took the fan blade off and attached a board to the middle, it will spin just as the fan blades did.... but way too fast.

Would a dimmer used to control low wattage lights be able to keep the rotations down or am I missing something? Thanks.
 
In my experience that'll kill the motor.

tis the season to look for a rotating Xmas tree stand instead ...
 
dus10 said:
I am looking to control the speed of a fan, thinking a dimmer may do the trick. I have a small, 3 speed oscillating tabletop fan that I am trying to convert into a rotating tabletop display. I thought if I took the fan blade off and attached a board to the middle, it will spin just as the fan blades did.... but way too fast.

Would a dimmer used to control low wattage lights be able to keep the rotations down or am I missing something? Thanks.
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The fan blades are connected directly to the motor shaft and there is no practical way of slowing that down to any practical turntable speed. You can gear down the motor to a practical speed, either using a gear-head motor, or using a small pulley on the motor shaft and a belt that goes around the outside of the turntable.

Or you can use something like a stepping motor which you can run as slowly as you wish. There are many small gear-motors and stepping motors available online, many of them surplus units at good prices.

Do you already have the round table part? What diameter? What speed are you going for? How much weight does it need to bear?
 
The type of motor is the key - DC motors with cummutators can have their speed changed by controlling the voltage. Most fans are AC motors that are locked to the mains frequency - so will try to run at the same speed no matter what. A few have two sets of windings to allow for a speed change. Also keep in mind that electronic dimmers do not reduce the mains voltage at all - they just allow full power for less time each cycle of the mains, so a light dimmer may make the motor overheat and produce some very nasty buzzing sounds. A quick trial should not be terminal, and will instantly either work, or absolutely not work. If the fan needs to be reused, even the test could cause it to overheat, probably voiding any guarantee or warranty it had.

A lamp fillament is very different to a motor! What will probably happen as you turn it on, is nothing, then it suddenly tries to run at full speed making a buzzing sound.
 
Interesting. I haven't experience any problems with the light. I thought (obviously incorrectly)
that a motor is a motor. It's designed for a router, so I figured it would work on a fan.

Good advice!

Peter
 
Me Myself & I said:
Interesting. I haven't experience any problems with the light. I thought (obviously incorrectly) that a motor is a motor. It's designed for a router, so I figured it would work on a fan.
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Raw motors are intended to run thousands of RPM. Especially motors made for high-speed applications like routers and fans. There is no "dimmer" known on this planet that will slow a motor like that down to the speed you need for a turntable. No conventional motor will turn at a speed that low, they are just not designed for it. The only kind of motor that will turn at that speed is a stepping motor.

Dimming a lamp and controlling the speed of a motor (especially if you are looking for very low speeds) is a completely different problem. The router speed controller will NOT control a router down even to 1000 RPM which is way too fast for a turntable.

As "j" suggested, 'tis the season to find a Christmas tree rotating stand, etc. There is absolutely no future in trying to run a turntable directly on the shaft of ANY kind of conventional motor, AC, DC, series, shunt, synchronous, etc. etc.
 
DaWolf85 said:
Wouldn't gearing it for slow operation work?
Like 360:1 gearing or something like that?
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Absolutely. That is the most workable solution to the question. And there are some very suitable low-speed geared motors available for very inexpensive prices (<$10)

But the notion of running a low-speed turntable directly from the shaft of a raw motor is completely impractical.
 
There is definitely a lot more to this problem than just decreasing the volate to the motor. You need some gearing. If you're looking to build a DIY turntable the best gadget to get is a rotisserie motor! Very smooth, very (VERY) high torque, and easy to work with because you can stick anything in the square shaft hole. Picked one up at a used shop for $3.00 but even new they're barely $30

Otherwise search low RPM motor on ebay. Lots of cheap options that would cost less than the price of a fancy dimmer switch. Even the tiny ones tend to be very powerful, because you gain torque by dropping RPM.
 
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