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[bkenobi]

I'm just posting to see if I'm missing something logically before I go install it to test...

I have a fan in my shower that pulls more air than I want.  As  result, it makes for a cold shower and keeps my wife from turning it on some days.  I've been thinking of installing a fan speed controller, but I have 2 issues with that.

1) There is no space to install one AND have a timer so I'd have to pick one or the other.
2) I have space to install the controller right into the fan case, but then I can't adjust it without pulling things apart (so it would be a 1-time setup).

Ideally, I'd be able to have the fan run at a slow speed when the shower is in use and then speed up when the person leaves the shower but automatically stay on for a few more minutes.  I have looked for a combo fan speed control + timer module, but have not found one.

The other day I was thinking that I may have made this too difficult (trying to force X10 into the solution, that is).  I figured I could just use a relay to turn on the fan at 2 different speeds depending on whether the shower light was turned on (since they are in the same unit).  I could then use the fan speed controller on one side of the relay and line power on the other leg!

Other than finding a way to keep things from vibrating and causing a low WAF racket, am I missing something as to why this wouldn't work?  I have several relays that I bought a couple weeks back, so I assume I just need a fan speed controller and I'm good, right?

http://www.allelectronics.com/make-a-store/item/RLY-453/120-VAC-RELAY-DPDT-12-AMPS//1.html

[dave w]

I could then use the fan speed controller on one side of the relay and line power on the other leg!
http://www.allelectronics.com/make-a-store/item/RLY-453/120-VAC-RELAY-DPDT-12-AMPS//1.html

OK If I understand: The relay coil will be powered by the light circuit. The common terminals of the relay will be fed line voltage from the original fan switch.  The N.C. terminals will got to the fan motor for high speed. The N.O. terminals will go to a speed control which then goes to fan motor for low speed.

Works in my book. You will be back feeding the speed control in the high speed mode, but with the input side of the speed control open circuited, I don't see a problem. 

[bkenobi]

It took me a second, but I think I understand what you mean by back feeding the controller.  Since it's an open circuit unless the relay closes the circuit, I don't think that should be a problem.  I just have to check that the fan will work with a controller.  It's a Nutone, so I'm pretty sure it should work fine.  I'll probably call tech support tomorrow with the model number just to verify though.

Thanks for the input!   

[dave w]

It took me a second, but I think I understand what you mean by back feeding the controller.  Since it's an open circuit unless the relay closes the circuit

Yes, The output side of the speed control will be fed 120V when the "high speed" contacts are closed. 

[bkenobi]

If that's a bad thing, then I could use the other side of the relay to isolate the fan speed controller entirely.  The relay is a DPDT and I originally was only going to use one side.  I could certainly hook up the output of the fan speed controller to the second side so that the live power won't back feed.

[dave w]

If that's a bad thing, then I could use the other side of the relay to isolate the fan speed controller entirely.  The relay is a DPDT and I originally was only going to use one side.  I could certainly hook up the output of the fan speed controller to the second side so that the live power won't back feed.

Whether you connect the "line" to the common terminals of the relay, or you connect the fan motor to the common terminals, you will still have 120V present on the output of the speed control when the relay is in the high speed (unenergized coil) mode. As long as there is no voltage on the input to the speed control I don't see how there could be a problem. If there was 120V on the input and output of the speed control at the same time there could be a problem (I don't know if it actually would be or not).

[pomonabill221]

  Usually, induction motors do NOT like chopped AC like a triac dimmer supplies.
  If it is a shaded pole motor (which most bath fans are, you can tell by looking at the motor and if there is one or two very heavy copper straps around the motor laminations, these are the "shades"), you could use a 25 watt wire wound 25 to 50 ohm resistor in series with the motor.  It WILL get warm, but if the resistor is in the fan enclosure, and mounted so that it does not touch anything plastic, the air being pulled thru the fan enclosure should keep the temperature under control.
  Then you could use an appliance module to control your relay coil (providing the coil is 110 vac), and use the N/C contacts to "short" or bypass the resistor (normal high speed), then when the contacts open (appliance module on and the relay pulled), the fan would receive reduced voltage thru the resistor.
  You could set the low speed "speed" by the value of the resistor.  I am using a 25 watt / 50 ohm resistor for my fan, but the larger the motor, the smaller the resistor value should be for the same speed.
  I would NOT recommend using a lamp DIMMER (or any kind of lamp dimmer) to control the motor speed because of the chopped AC from the triac, and it WILL hum or buzz alot, if it runs at all, and it can cook the motor!

[bkenobi]

Oh, I have no intention of using a dimmer module to control the motor speed.  In fact, this will be a fully non-X10 setup.  I'm intending to use a standard fan speed controller typically used on a ceiling fan.  I have to verify that the motor being used in the bath fan will work with one of these.  I'll be contacting Nutone to verify if possible.  If they can't help, I'll just get a controller and give it a go.  I've read that this should work, but I don't know yet.  Anyway, this will be strictly off the shelf components.

I'll have to check the fan like you suggested to see what kind it is.

[pomonabill221]

Oh, I have no intention of using a dimmer module to control the motor speed.  In fact, this will be a fully non-X10 setup.  I'm intending to use a standard fan speed controller typically used on a ceiling fan.  I have to verify that the motor being used in the bath fan will work with one of these.  I'll be contacting Nutone to verify if possible.  If they can't help, I'll just get a controller and give it a go.  I've read that this should work, but I don't know yet.  Anyway, this will be strictly off the shelf components.

I'll have to check the fan like you suggested to see what kind it is.

  OK!  The ceiling fan controllers are usually 3 or 4 speeds (including high) and use capacitors to reduce the voltage to the motor.  They are great and do NOT make the motor hum at all!
They should work great for your application as some ceiling fans use shaded pole motors as well, so your application should work with no problem!
  The speed control will NOT care if it is back fed either!  You would basically be shorting (or bypassing) the capacitor(s) in the speed control when on high... no problem!
  This would allow you to select one of 3 (or 4) speeds for your low setting also!
Great idea!  Hope it works for you!  (I think it will).

[bkenobi]

Good to hear.  I didn't have time to get to the hardware store on the way home, so I'll either head out this evening or tomorrow.  Either way, I think it should work pretty slick.

[pomonabill221]

Forgot to add...
  You will still need a relay to interface an appliance module to the dimmer/fan.  That way the appliance module will pull the relay (110vac coil) and the contacts will switch the speed control in and out of the circuit.
  This is to insure that you don't have any line to line cross coupling which could result in the appliance module feeding that branch circuit, bypassing that branch circuit's breaker protection.  It would also overload the appliance module if something tripped the breaker on that branch.  Sorry if confusing... just to be safe, use a relay for isolation.

[dave w]

  Sorry if confusing... just to be safe, use a relay for isolation.

I think he is pomona. Did you read the OP?

[pomonabill221]

  Sorry if confusing... just to be safe, use a relay for isolation.

I think he is pomona. Did you read the OP?

Yes I did but I wanted to confirm about using a relay for isolation as he seemed to have several different methods that he wanted to use, that's all.

[dave w]

bkenobi,

Brain was asleep or dead in my previous posts about the DPDT 120V relay.

You could also simply short across the input to output of the speed control with one set of N.C. relay contacts for the high speed mode. The fan would be high speed until you turned on light which would open the contacts putting the speed control in the circuit. Wiring would be simpler.

[bkenobi]

That's basically the idea.  I spoke to NuTone tech support this morning to verify that my specific fan motor can handle speed control.  They said that I can use either a 3-speed or variable speed fan controller and I'll be just fine.  The only thing to verify is that I get a controller that can handle more than 1.7A.  I think all the units I've seen are spec'ed to 5A, so that should be a non-issue. 

Here's the fan I have:
http://www.nutone.com/product-detail.asp?ProductID=10199

I've attached a simple schematic of what I'm planning on doing.  And yes, I realize there's more connections on the fan speed controller than just power.