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Discussion Starter #1
Any electricians here?!? I have a weird question about 120v motors. :2huh:

I recently replaced the inoperable blower fans in my fireplace with new ones. I went with a newer style that moves more air with less current draw. They work great, but are too loud. Not loud from the fan, but rather too loud from the air movement.

My question to the electricians: Can in install a “dimmer switch” so I can control the speed of the fans? If I could slow them down, they would be perfect. I’ll have to check to see if the motors are variable speed, but I suspect they are not. If I use the dimmer switch, will I fry the motors? :bawling:

And help would be appreciated. :thumbsup:
 

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As long as the motor is NOT a capacitor start or a capacitor run motor you can use a speed control. It is probably a shaded pole motor
and they are fine with a speed control. You will have to make sure it doesnt stall or the motor will burn up.

If it is a small enough motor you could always use an X-10 controller and make it remote controlled!
 

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You should be fine with a dimmer switch. Basically, you're limiting voltage to the motor. Same thing as if you put a 240v light bulb in a 120 socket. The light will be half as bright and last nearly twice as long. Might want to get a second opinion though, as I'm only getting a B in my ag electrical class...

Joe
 

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It honestly depends on the motor. For most applications a dimmer switch will be fine....but I think I have a spare variable frequency/ voltage drive at work...haha...

--Craig
 

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tbirdbrain said:
As long as the motor is NOT a capacitor start or a capacitor run motor you can use a speed control. It is probably a shaded pole motor
and they are fine with a speed control. You will have to make sure it doesnt stall or the motor will burn up.
Should add to this, the reason you don't want to slow a cap start/run motor is b/c the starting mechanism realeases due to centrifigual force (directly realted to the motor speed). So if it is turning slow enough for a long time, the starting mechanism won't release and there goes $150 (or whatever you happened to pay for the motor)

But for a fan, I wouldn't see a cap motor being used. Prob a shaded pole or a split phase motor is being used, since they wouldn't need the starting torque of a cap motor.

Joe
 

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A dimmer switch should be okay but be careful that it is rated high enough for the current you will be drawing.
A lot of the cheap dimmer switches you buy are only good for 500 or 1000W.
This equates to a maximum of about a 10amp draw for the 1000W dimmer.
Many blower motors are pretty close to 10amps if not more.

Be careful as you do not want to start a fire. That fan would spread the flames real well.
 

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Discussion Starter #7
Thanks for all the input guys! What everyone is saying is what I thought, but I'm a lot more up on electronics than I am on 120v wiring. These are just a pair of 6" 120v fans that I doubt pull more than a few amps. But I will double check.

Thanks again. :thumbsup:
 

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Why does your fireplace have a fan?

Ours doesn't have one and it works just fine. All we do is warm it up with the gas only and then we throw a couple of logs down. The air starts sucking it up and out automatically.

Just curious?
 

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Midnight said:
Why does your fireplace have a fan?

Ours doesn't have one and it works just fine. All we do is warm it up with the gas only and then we throw a couple of logs down. The air starts sucking it up and out automatically.

Just curious?
I'm going to guess these are the kind of fans that circulate air out into the room. The air they move is the stuff that is heated by the metal? firebox and would otherwise be "wasted" heating the chimney or surrounding building structure.
 

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Discussion Starter #10
The fans are installed into stone ductwork around the firebox. It increases the efficiency of the fireplace by circulating the air around the heated box. The fan isn't anywhere near the fire or the flue. An awful lot of heat goes out the flue in a fireplace. By building ductwork into the masonry around the around the firebox and pulling air into and out of that ductwork it really puts heat into the room.

I have thermostatically controlled vent-free gas logs in my fireplace which just used to be a regular wood burning fireplace. It works fine, but will run less if I use the fans since it is using the heated firebox to also heat the room. :thumbsup:

And are you saying that you put regular wood longs on top of gas (LP or Natural Gas)burners?
 

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94 Daily Driven 4.6L said:
Thanks for all the input guys! What everyone is saying is what I thought, but I'm a lot more up on electronics than I am on 120v wiring. These are just a pair of 6" 120v fans that I doubt pull more than a few amps. But I will double check.

Thanks again. :thumbsup:
If you could post the values that are on the motor itself (hp rating, amps, etc) I could let you know a little more. I'm doubting they would pull 10 amps, but with that info, you'd be able to pick a controler that would be suitable for the motors.

Joe
 

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Wouldn't a potentiometer work? Like the switch for our dimmers. Controls the voltage being dropped by the fans. As resistance across the potentiometer goes up, the resistance goes up, and lowers the voltage dropped across the fans. The problem would be getting a potentiometer that can take that much current. I haven't gotten much into actually measuring and working on electrical components other than small relays, capacitors, and coils, but you should be able to measure the current by using a multimeter, cut the cord to the positive or negative, put the multimeter on AC amps. Make sure the power is off first. Put the positive on the negative output of the fan, and the negative on the wire that goes back to the negative in the outlet or whatever. Then reconnect the power. The average current should show on your multimeter.

If you put them in series, they would run at 60V. That would only work if they are capable of running on that amount of voltage. I'm tired, so don't take me too seriously.
 
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