A Major SNAFU has reared it ugly head

[Aardil]

AHhhhhh the saga continues

Well after working diligently to make variable speed fan swiches work, alas it didnt .

The main problem seems to be not enough resistance in the fans to make the switches work correctly. Using just the fan there is Absolutly no fan movement untill you reach about 70% of wide open. from that point there is little to no increase or decrease in speed. So much for 20 bucks a piece slide controls.

OK back to the home depot and I lucked up ( If you can call it that ) they had some 3 speed fan switches that were also slide type. COOL I can live with just 3 speeds. Especaily for a buck 25 each Well it was not to be either
Hi speed and medium speed are the same and low spped is just barely short of hi speed I could tell a bit of difference by how loud the fans were but not what I was hoping for.

The only way I have determined to make the fans speeds work correctly is to put a 75 watt bulb in parralel with each fan. Tried a lower wattage bulb and it met with basically the same results as no light bulb at all.
I aksed around and a resistor of large enough capasity to do the same thing would generate more heat than the light bulb does so thats out of the question.

So I dont know what to do. Thought of changing the fan circut to 12 volts but then I need a power converter ( which I dont have room for ) and ditch my 3 120 volt fans. While this is the most logical route, the whole purpose of going 120 volts was because there is no power converter in that case.
I am still working on a solution but running out of Ideas.
I couldplace a 12 power converter outside the case or hang light bulbs under my desk to burn off the power ( painted glow in the dark green for that UV effect )
any other Ideas?
I am open
Aardil

[airspirit]

I've got two. First off, the controller you got isn't the right thing. They have dial style controllers at Home Depot that cost $10 that function like a potentiometer on a 12V fan. You could try to use the right part for the job.

That said, you could also emulate the resistance of the light bulb, if indeed that works.

120V x I = 75W, I = .625A
VI = R
R = 75 Ohms

Put a 75 Ohm resistor that can handle the power load in the circuit in series and you'll be pimpin.

Honestly, since you'll be spending $$$ on resistors to get that kind of power load, you're better off buying the right part for $10. It is called a ceiling fan controller switch and has a knob like a dimmer.

[Aardil]

not trying to sound Smart arsed but the controls I got are for fans not lights.
Lutron Skylark
Fully Variable Controls:
For use with ceiling paddle fans, ventilation or exhaust fans
SFS-5E- Slide-to-off
single pole fan control
5A fan

The only differance in what you are talking about and these is these are slide control the ones you are looking at are rotary.

Again about 70% full power to get fan moving ( with or without additional light bulb ) After it is spinning I can reduce power to around 50% before fan stops. Without light in line Fan speeds up and runs at almost full speed as soon as you get to the 70% range and does not decrease when lowering setting. Once 50% is reached the fan stops.
With the 3 position slide the $1.25 ones I get a very low ( too low to be of any use speed) a medium that is higher than I would like and a wide open on hi. Of course this is with the light bulb in parralel. With out light buld Hi and medium are the same speed and low is a bit lower but still higher than the medium with the Skylark switch.
The more I test I am leaning towards 12 volt fan set up.
Maybe I am just tired but I am comming up zeros on a way around this problem

Aardil

[airspirit]

That is what I'm talking about, bro. You want the dimmer style controller rather than the three-speed controller. Basically it amounts to a high power potentiometer (variable resistor) that sits in series with you fan(s). You can set your fans to any speed within the resistance curve. They are designed for use with the huge power hungry ceiling varieties, so you will have no problem with overheating. The problem with the three speed types is they depend on a high power (W) fan running, which is why you have to add resistance (bulb) to make the switch work. Your fans don't draw enough amperage to cause the resistance values of that 3way to affect your current appreciably. Really, try a dimmer variety, like this one:

http://www.homedepot.com/prel80/HDUS...ource=HOMEPAGE

It is designed for 5 amps (575W max power), so you won't be taxing it with your piddly 60W of fans. Keep in mind, though, that you will probably need to have all your fans on the loop, and you won't see much change until you're halfway toward off.

[MadDogMe]

He said he tried a variable type slider and a three speed setting type, sounds like the variable just did'nt have the 'resolution' needed. I have the same problem with a V/R on my 12v fans, it's almost like an on/off switch, but I can just tweak it so I take the edge(noise!) off full power, which is all I want...

I'd bury the hatchet and go 12v :shrug: , at least you can get the right V/R for the job/ampage you want then, for total control of the range you're looking for...

[bigben2k]

I have a small desktop fan, with which I use a light dimmer. Works just fine, been using it for years.

The trick is that the dimmer has to be rated way above the power of the fan, because the power consumption of a fan varies with the AC cycle (i.e. it consumes more power at the peak of the AC wave, more than a lightbulb).

If I remember correctly, my dimmer is rated at 300W, and the fan is less than 100 Watts.

[airspirit]

If that is the case, then find a potentiometer (that's really what the part is) that is rated for less power (and therefore provides less resistance). Follow Ben's example.

[Aardil]

OK
Dont know if anyone here is an A/C tech or not and I sure as hell aint one.
As they say the proof is in the pudding.
Talked to the electric guy at Home depot and he said there is no way the rotary switch will work either, what is needed is a way to vary the frequency not the voltage and the little Radio crap fans are not made to run at variable volts or frequency although if I go to a specialty shop that deals in control curcuits they may have some type of controller that may do the job.
Alot of mights and maybe's and I know the place he is talking about, want a fuse? We have a $25 minimum invoice charge.

Well Since I do have a spare 12 volt converter and all I would be out is the money I spent on fans and swithes, I believe the time has come to go back to 12 volts.

Pity converter is gonna have to go outside the case ( not enough room) . At least with 12 volts I know I can build a totally automated fan system where no external control will be needed.

Oh well back to Rad Shack for a bunch of pieces parts and start building the control network.

Should have the cooler box completed by next weekend and the blocks will be in the following week. I will post some pics of the final creation when I get it finnished ( not sure what I am gonna do with the face plate since now it has 3 slider switches in it that have to come out) . Hmmmm Maybe LED readouts for Res temp, feed temp and return temp? Just thinking out loud

Aardil

[bigben2k]

Home Depot would tell you that... The theory is sound, for an AC motor, but we're just talking about an AC fan here, not a 4 feet tall warehouse ventilator.

I'm glad that you found a solution. Too bad you couldn't get a dimmer to work for you, like I did.

[airspirit]

I'm going to be trying to wire a similar dimmer style variable 600W control switch into two Comair Rotron Caravels tonight. I'll let you know what's going on with that when I'm done. Between the two fans, I'll be using about 200W (that seems like a lot of power for two fans, but these things pump air like sumbidg'z ... I gave one a test this morning and was like holeeecrapoleee!), and I figure all of my adjustment margin will be in the bottom-most part of the variable resistance (highest resistance in ohms).

As far as my understanding of fan controls for AC goes, the fan control should work. Many people around here have had good luck with them, and hopefully I'll be able to say the same. I'm just going to plug the fans into a powerstrip (non-regulated) that has been modified with the control switch like so:

[airspirit]

As far as being able to control the fan speed, I just had another thought. You typical desk fan usually has three settings: off/high/low. Basically, the settings mean: no conx/low resistance, on/high resistance, on. Same thing with your typical box fan with a speed dial, all that thing is is a high W potentiometer. If you really have problems, tear up a cheapo WalF*rt box fan and use the control switch in it. That should only run you about $10.

[Brians256]

Can someone unconfuse me? I am unsure of whether these fans are 120VAC or 12VDC motors. If they are AC motors, you want the same type of switch used to control ceiling fans: triac based. If they are DC motors, then you would want a slider controlled rheostat.

If I understand them correctly, triac based speed controllers do not change the frequency; they control the amount of time the AC signal is turned on. They chop out part of the sine wave so that the frequency stays the same. In order to change the frequency, you would have to have a fairly complicated circuit that regenerated the AC sine-wave.

The rheostats are high powered variable resistors that change the voltage supplied to the fan motor. That sounds more like what is being talked about, since many motors have a much higher voltage required to start versus the voltage at which they will stall. If it is DC, you might consider PWM to achieve a wider range of speeds, but it might add a bit of buzz to your motor noise.

[airspirit]

Brian, you're right. I did a stack of research and came to the same findings you did and unconfused myself. The ceiling control fan that I bought (one of the ones he bought as well, the Lutron variable controller) does just what you're saying. By chopping it like you described it reduces the force on the AC induction motor causing the fan to slow relative to the frequency of the AC wave. Yar. I think how Aardil screwed up, possibly, was by putting the controller on the wrong cable, notably, the ground line. I don't see how it could have been done, but it would cause the controllers not to work, or, if by some freaky fluke it did, there would be virtually no change. You must make sure that the controller is on the black line (mod a power strip and you'll have three lines: white/black (AC), and the green (ground). They will always be this color, so just mod the black line, and any AC fan plugged into the power strip will be controlled by the same circuit (excellent for use with a string of identical fans with similar characteristics like the ones I'll be using). Again, I'll report my findings either tonight or tomorrow, if I can get my lazy butt up to doing it.

[Aardil]

Well I can answer one question, I was on the hot lead of the Ac line ( black wire). After much brain farting I came to the conclusion that the problem was in the fans themselves not in the switches.
I believe that the problem was that the fans ( Rad Shack 120 V AC) didnt have enough resistance to pull the fan speed down as I thought it should. Resistance may be the wrong terminoligy but I hope you get what I mean.
Anyway, It is a mute point for me as I have completed the project by going to 12 volt DC fans and using the Automatic control board that I have another thread on.

Good luck on getting 120 AC to work, I hope it works for you.

Aardil

[airspirit]

Okay. I'm glad you got it working. I'm hoping that I don't have the problems you had, but at 200W of draw, I shouldn't be in the same bucket of worms (plus, I agree: Rat Shack fans should be avoided like the plague ... they are ugly, loud, low performers, and generally are my own personal antichrist when it comes to cooling *blech!*).

[airspirit]

The circuit caused the fans to acquire a wierd buzzing sound, but worked fine. I have a full range from full-on to nearly nothing.

[Aardil]

YAY.
at least it worked for you and it kinda proves my thoughts that the real problem was with the Rad Crap fans.
Want a few Rad crap fans?

Aardil

[airspirit]

No, but I do want to figure out how to stop the buzzing my fans are making. I found that they are actually quieter running at full speed if I take them off of the control circuit because they don't make that buzzing. How wierd is that? I thought that that wasn't supposed to happen with a fan controller? It's not like I'm overloading it ... I have 200W on a 600W controller.

[airspirit]

Used a dehummer circuit and it works beautifully. The settings are wierd to MAKE it work, but it works nonetheless.