Easiest way to slow down a 240v AC fan?

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chylld
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Easiest way to slow down a 240v AC fan?

Post by chylld » Mon Jan 24, 2005 10:31 pm

heyas,

i have a 240v ac pedestal fan, what are my options when it comes to slowing it down? (the slowest setting is too noisy for me)

the only option i'm aware of is a 240v-110v step-down converter, but that's more expensive than buying another (quieter) fan :)

any tips?

ferdb
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Post by ferdb » Tue Jan 25, 2005 3:29 pm

There is no super cheap method. What is reasonable depends on how much current your fan pulls. You can use series resistors of sufficient wattage to reduce the voltage on the fan, they generate heat though. You can use series capacitors to do essentially the same thing without generating excess heat, but choosing the right value is trickier since the inductive impedance of the motor will be cancelled out by the capacitive impedance to a greater or lesser degree and you can actually end up with higher than 230V across the motor. If you have one of those 3 or 4 step ceiling fan controllers you can try and see how that works with your specific fan. Those have 2 capacitors in them and a switch arrangement to give you 3 different capacitance values or straight through or off.

Usually Triac type dimmer circuits work poorly or not at all on heavily inductive loads like motors, and they can also make a lot of noise in the motor.

Using a transformer will work well, however you need to find one cheap enough. Perhaps something like this
http://www.allelectronics.com/cgi-bin/c ... type=store

Sometimes surplus stores will have something usuable. If you hook the transformer up in autotransformer configuration you can use the secondary windings to buck the output voltage down from 230v. A transformer like this
http://www.allelectronics.com/cgi-bin/c ... type=store
can be wired to give a variety of voltages lower than 230V.

However the cadillac of AC fan controllers is a Variable transformer like this
http://www.allelectronics.com/cgi-bin/c ... type=store

it will let you set your fan to whatever speed you feel like with no extra heat or noise, and works on any reasonable sized fan. This is what I use.

ferdb
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Post by ferdb » Tue Jan 25, 2005 3:32 pm

It just occured to me you are probably on a 230V system and would need a 230V compatible Variable transformer (Variac) for your application. I would direct you toward Ebay, where I have seen a large variety of such items that would satisfy your requirements. Good luck

chylld
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Post by chylld » Tue Jan 25, 2005 11:21 pm

thanks for ur reply ferdb, i'm starting to understand a bit more about the subject now :) i came across the variac in a previous search but it was too expensive for my needs.

i'll take the fan apart sometime and see if i can figure out how it works.. with any luck, i might be able to replace a few of the components and problem solved :)

ferdb
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Post by ferdb » Wed Jan 26, 2005 2:58 am

usually multi-speed fan motors have different winding arrangements to allow the different speeds. Not something you can modify really.
A quick and dirty way to slow it down though may be to put the fan in series with a light bulb, try different wattages to see what you get.

chylld
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Post by chylld » Wed Jan 26, 2005 3:20 am

ferdb wrote:A quick and dirty way to slow it down though may be to put the fan in series with a light bulb, try different wattages to see what you get.
that sounds like a very interesting idea! how do i go about wiring it? if you have time, could you please describe how i'd do it?

i have a fair understanding when it comes to DC electricity, but i have little idea about AC. all i think i know is that one of the pins goes from +x volts to -x volts at 50hz (or 60hz, whatever it is here) while the other pin does the opposite. or am i wrong already? hehehe

ferdb
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Post by ferdb » Wed Jan 26, 2005 3:47 am

you can stick the bulb in a lamp obviously. connect one wire (or prong of the plug) of the lamp to one wire of the fan. Connect the other wire of the lamp to one wire of the AC socket, connect the remaining wire of the fan to the other wire of the ac socket. You should end up with a loop from one AC wall socket contact, through the lamp, then through the fan, and back to the other AC wall socket contact.

Krispy
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Post by Krispy » Wed Jan 26, 2005 5:31 am

ferdb wrote:
Usually Triac type dimmer circuits work poorly or not at all on heavily inductive loads like motors, and they can also make a lot of noise in the motor.
You are dead right about this!
I connected up an inline dimmer to my AC fan & it was partially uncontrollable. I had to rotate the dimmer to find a sweet spot, otherwise the fan would just freewheel & the extra motor noise either way was considerable. As ferdb says this is not the way to go & I never solved this problem.

The light bulb technique sounds really interesting.
chylld, could you let us know what effect the different wattage bulbs have?
Many Thanks! :)

chylld
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Post by chylld » Wed Jan 26, 2005 11:21 am

as soon as i get some free time i'll definitely try it :) i'll probably go and modify a double adapter to keep things safe and simple.

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