Noob needs help

[Empty V]

Hey everyone this is my first post here. I'm an A/V guy and an editor/special effects artist that has a limited background in component electronics, obviously.

I've got the fan pictured below that has a 115V AC plug. There are no switches or toggles, just a power cord and I need to incorporate a variable speed control into it. I'm guessing that I need to solder inline with the power cord a pot but not sure. On the front sticker it reads:

115V~AC 50/60 Hz
1 PHASE 6/5.5W
IMPEDANCE PROTECTED

Can someone please verify that a potentiometer inline with the power cord would be the right way to go. If so, which pot to use and what to solder where. If not, what should I use?

**broken link removed**

Thanks for the help, I really appreciate it!

Billy

 

[audioguru]

There are many types of AC motors. I don't kow which type is used in your fan.

A pot is not used to control the speed of an AC motor. A pot must be huge and expensive because it would get hot. A little electronic speed control circuit is used if the motor's speed can be controlled. Some fans can have their speed adjusted by an AC light dimmer circuit.

Some AC motors run at the 60Hz mains frequency. Then a complicated circuit that changes the frequency can control their speed a small amount.

 

[Empty V]

There are many types of AC motors. I don't kow which type is used in your fan.

A pot is not used to control the speed of an AC motor. A pot must be huge and expensive because it would get hot. A little electronic speed control circuit is used if the motor's speed can be controlled. Some fans can have their speed adjusted by an AC light dimmer circuit.

Some AC motors run at the 60Hz mains frequency. Then a complicated circuit that changes the frequency can control their speed a small amount.

I'm thinking of something that I can solder inline with the power cord to control the mount of voltage, like a light dimmer. Maybe a dimmer is the best way to go, any thoughts?

Billy

 

[Torben]

Hi Billy,

According to the data sheet, your fan has a shaded pole induction motor. I am no expert but I'm pretty sure that it will not be at all happy with a potentiometer limiting the voltage. For that matter, neither will the potentiometer.

Disclaimer: what I think I know about the topic I learned from Google. Take into account that I am not speaking from deep personal experience here. Anyway, some people report good luck using lamp dimmers to control these things, while others have trouble using dimmers--they get stuttering, intermittent operation, and so forth.

If you have a dimmer lying about you could try it and see what happens.

Are you looking to just buy a controller or would you like to build your own?

What price range are you looking at? How many do you need?

What range of control do you need? If I am to believe what I've read then I think you can only get a limited range of control over a shaded pole induction motor; something like 50%-100% of speed. i.e. I don't think you can turn it down all the way. The upside is that supposedly you get a fairly good ratio of fan speed change to volume of air moved so it might be sufficient for your purposes.

Anyway, some of the more experienced member will be able to guide you better; I'm just trying to fill in some gaps.


Good luck!

Torben

 

[ecerfoglio]

I'm thinking of something that I can solder inline with the power cord to control the mount of voltage, like a light dimmer. Maybe a dimmer is the best way to go, any thoughts?

Billy

Yes, you can use a dimmer. Try to get the ones used for ceiling fans. Perhaps you will need to ass a junction box to house it.


The motor is an AC induction motor, but if it is driving a fan you may control its speed controling the voltage (ie with a dimmer).

As it is Impedance protected it will not destroy itself if it stalls and is unable to spin (ie if the voltage is too low to start)

 

[Pommie]

Can you get a 12V fan that is the same size. It would be a lot easier to control.

Mike.

 

[Ubergeek63]

In induction motors speed is related to frequency so you will have little, if any, luck getting the speed to change using normal methods.

You might be able to get it to slow down with a pseudo sine variable frequency inverter, but it would be very noisy and hell on the bearings.

 

[ecerfoglio]

In induction motors speed is related to frequency so you will have little, if any, luck getting the speed to change using normal methods.

You might be able to get it to slow down with a pseudo sine variable frequency inverter, but it would be very noisy and hell on the bearings.

In induction motors speed is related to frequency, but you can slow it down reducing the voltage.

The problem is that the torque is also reduced, and with a "normal" load (constant torque) it won't be able to spin at all. A "standard" motor, if not allowed to spin, will overheat and destroy itsefl .

BUT

>>> If the load is a fan, when you reduce the speed the torque is also reduced - A fan takes a torque that is proportional to the square of the speed (and its power is proportional to the cube of its speed)

Almost every "domestic" fan (like ceiling fans) have a means to reduce its speed, and this regulation is achieved reducing its voltage (with a series reactance or with a dimmer).

>>> If the motor is marked as "Impedance protected" it means that, even at cero speed (stalled) and with full voltage applied, it will not reach dangerous temperatures.

So you don't need a frecuency inverter, the best method is a dimmer.

There are some dimmers that are built to drive only lamps, they may not accept inductive loads.

Some dimmers are built to control the speed of fans and they will work OK with your motor. Think of it as just a "small ceiling fan motor"