2) I have a whole-house attic fan that I'd like to put onto relay control. The fan currently is controlled by a manual 2-speed switch....so it has OFF, HIGH, and LOW as specific switch settings. I'm just GUESSING that "High" probably sends the whole 120v up there, and LOW sends something less (there's 2 power wires, neutral, and ground coming off the back of the switch). I'm trying to figure out how I can control this via ALC relays. Any ideas?
I doubt very much that different voltages are involved. That would make for a pretty expensive controller/switch.
Instead, I think the motor has dual windings (hence the reason you have two power wires). On low, one is energized and one high, both are. If so, all you need is two relays to control the speed.
You can carefully verify the above. Get a voltmeter, set it to AC (high voltage) and carefully measure what goes out when you set the switch to off, low and high. If the last two show 120, then the above theory is right.
Note that inductive loads require a relay with a capacitor across the contacts to keep the resulting sparks in check. Otherwise, the relay will not last long. So you want a relay that is rated for inductive loads, not just resistive (i.e. for lights).
If you are at all uncomfortable with the above, then get an electrician to do the work.
I'll address question 2 first...........
Attic fans certainly do come in a variety of types. But some do NOT use motors with a variety of taps/run voltages. Instead they use a controll switch that does the tapping (my son has one of these in his house). Not sure of the price as it was installed when he bought the home. Your situation sounds like it has two outputs and the motor has two taps (or 1). So what AMIRM advises is dead accurate. There are a number of thoughts about changing the speeds though.
First, understand that dimmers do not work with motors (at least they are not supposed to). However, I like to use the text book as the basis for fact while also being a doubting Thomas and want to test things for myself. So I also spend time trying things on my own - A kind of "burn and learn" approach.
I currently have a 1/2 HP ceiling fan motor on a 600watt X-10 PCS Scenemaster dimmer. It makes no noise, and does not run hot until I slow it down to a crawl (which I would never do normally). I have 4 years run time with this confiuration in my media room. However...... I also tried the same thing with a smaller 1/4 HP motor in my guest house with terrible results. NO TWO INDUCTIVE LOADS ARE THE SAME. Some of this makes little sense when you compare to what is SUPPOSED to be.
I also have a 600watt ALC dimmer running another 1/4 HP ceiling fan and it works fine. In my attic, I have two roof exhaust fans that ran fine for 1 year using a 600Watt Smarthome MFG. X-10 dimmer. I did not try to slow them, only to run at full speed. This year, the switch kept losing it's programmed X-10 address but would still work fine otherwise. I did replace it with an ALC relay though.
In our training center at SETNET we often try "TO LET THE SMOKE OUT" of devices. And we often succeed. WHile strange things can happen, sometimes you never know until you try. While we don't propose you use dimmers to change speeds on inductive loads, I also know that CocconTech readers are excellent DIY'ers and like to experiment (be safe above all else)!
The changing of power factors to make inductive loads easier to control is another place we experimented. Adding capacitors does change things, but like dimmers controlling motors or relays mixed with various AC voltages, it's not the way the CODE experts would advise you to go!
In all the years I have been in the Home Automation business, there has never been an inexpensie solution to speed controlling motors. The technology exists in the form of SCR's (Silicon Controlled Rectifiers). However it's expensinve, large and takes a changing analog voltage trigger to output the various AC voltages to speed control motors. Out of the question for home installs.
Yes, I do use some dimmers for this and honestly say that I have spent more money burning out switches while on the hunt for the perfect dimmer than it was worth. After all our research and all my "burn and learn" I can say this. "There is no brand of automated dimmer that I can promise will work". If you want to experiment and don't mind letting the smoke out on occasion, then you can look for dimmers on your own (once you let the smoke out, it won't go back in)! Of course the advice to use qualified Electricians is strongly offered. But try to find one that would put a dimmer on a motor! I would use the
ALC 900Watt dimmer or the
PCS 1000 watt UPB Dimmer if you want to experiment.
In summary, using a relay (inductive type) is your best bet and forget about controlling the speed!
Now for your question about enclosures. If you don't want to use self tapping screws and mount them onto a metal backplate (crude), then consider a small structured wiring enclosure.
OnQ LEgrand 14" or the
SCP 14". Both accept OnQ modules, with the SCP version being cheaper.
Hope this helps...
TS
