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Old 01-07-2009, 09:57 PM   #1
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Using potentiometer as fan control


I have a fireplace insert with a 3-position switch, low, med, high, problem is, the low is too high. Would it be possible to only use the low speed wire (red) and hook it to a potentiometer to further slow the fan or is there a better alternative?

There is one black for the hot, the Red is low, Blue is med, Black is high, 4 wires total on the factory 3-way switch.

I have one of these from Radio Shack, my fan is rated at 2A on high.


http://www.radioshack.com/product/in...ductId=2062298

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Old 01-08-2009, 04:27 AM   #2
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Using potentiometer as fan control


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Originally Posted by i6pwr View Post
.....I have one of these from Radio Shack, my fan is rated at 2A on high.....
http://www.radioshack.com/product/in...ductId=2062298
Look closer at your Radio Shack #271-215 Potentiometer
It should say the power rating is .05W

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Originally Posted by i6pwr View Post
..... my fan is rated at 2A on high.....
Now the Power dissipated by your Fan at full power is P=IE or ~240W
To use a pot hooked up as a series limiting resistor means that for example a 10% Power reduction (decrease speed) the Power dissipated by the Pot will be in the 20W range.

Here is some one who tried to use the same Radio Shack Pot as a speed control on a 3V hobby fan motor:
What is the right size pot for my little hobby motor? - All About Circuits

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Old 01-08-2009, 06:30 AM   #3
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Using potentiometer as fan control


Well, that explained my smoke bomb as well .

Figured the 3 amp rating kinda overran the .05W rating. After some searching I came up with this...

http://www.electricmotorwarehouse.com/kbwc.htm

Question I have is the 3 speed wires going to the fan, red, blue, black...ow, med, high respectively, would I just attach the black hot wire and the black high speed wire and let the kb switch control the speed?

Thanks again for the help.
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Old 01-08-2009, 09:55 AM   #4
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Using potentiometer as fan control


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Originally Posted by i6pwr View Post
Well, that explained my smoke bomb as well .

Figured the 3 amp rating kinda overran the .05W rating. After some searching I came up with this...

http://www.electricmotorwarehouse.com/kbwc.htm

Question I have is the 3 speed wires going to the fan, red, blue, black...ow, med, high respectively, would I just attach the black hot wire and the black high speed wire and let the kb switch control the speed?

Thanks again for the help.
I believe that is the intent. The high speed is the natural speed of the motor, so that would be the winding to insert the speed control into.
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Old 01-08-2009, 12:10 PM   #5
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Using potentiometer as fan control


Put an incand. lamp in series with the fan motor. 100w might be a good place to start, then go up or down in wattage until you get the speed desired. Less wattage=less speed.
If you then measure volts across the fan and current into it, you can figure out what kind of power resistor and wattage you need for a more elegant fix. Try to mix and match 10 resistors from Hosfelt.com to get the desired values.
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Old 01-08-2009, 09:33 PM   #6
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Using potentiometer as fan control


That was my next question....I figure the other 2 speeds I can use if desired, just need to slow the low down a bit without stalling the motor, wasn't sure if a resistance load would work on a motor, thought it had to be a PWM design.

I will try the bulbs, what type of socket housing can I use, I assume it should be two wires, 1 in and 1 out but are these avail from HD or Lowes?

Seems like a typical science experiment but just want to get it right.

Thanks again for the help.
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Old 01-09-2009, 01:11 AM   #7
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Using potentiometer as fan control


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Originally Posted by i6pwr View Post
.... what type of socket housing can I use?
Here is one from Lowes:
Cooper Wiring Devices at Lowe's: Porcelain Keyless Ceiling Lampholder

You're not going to find any 10 cent resistors. We are talking about power.
25 Watt Resistors, 25 Watt 5% Wire Wound Resistors


This might be a fun experiment but remember the last smoke test.
Any liability from this completely illegal kluge will be your responsibility.
When the Insurance Investigator sifts through the ashes and finds your melted illegal kluge he will immediately cancel any claims.

Even worse what if a child, or visitor, or housekeeper, or repairman, or Pet gets Smoked? They don't know what is going on in that funny looking box you built.
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Old 01-09-2009, 06:46 AM   #8
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Using potentiometer as fan control


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This might be a fun experiment but remember the last smoke test.
Any liability from this completely illegal kluge will be your responsibility.
When the Insurance Investigator sifts through the ashes and finds your melted illegal kluge he will immediately cancel any claims.

Even worse what if a child, or visitor, or housekeeper, or repairman, or Pet gets Smoked? They don't know what is going on in that funny looking box you built.
.
Yeah, I know

All this is contained under the fireplace insert, only the "ON & Speed" switches are accessible.

Whatever I plan on doing it will surely be inside some type of housing or possibly a grounded junction box if there is any exposed wiring. The insert actually contains the blower/wiring rather well, definately not looking for an insurance claim denial from a homegrown fan .
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Old 01-10-2009, 01:31 AM   #9
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Using potentiometer as fan control


I wouldn't use a resistor to control the speed of any motor that doesn't have brushes in it. The chance of burning it up by lowering its voltage is pretty good.

A basic light dimmer won't work either. Well, it'll work, but not for long.

A fan speed control, like for a ceiling fan or a bathroom fan will work best. It'll be doing just what it is designed to do, controlling the speed of a fan.

Rob

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