Dimmer switch

[BudMan]

Could you use one to controll speed of fan?

In my mind it will do the same job? The ones from b&q are rated at 250watt. And only 6 pound odd.

[whitewidman]

No you can't unfortunatly it's got somthing to do with the altered wave form (or sumat like that) in the incoming power so the fan stalls and will burn out. you have to have a proper fan speed controler with some clever wigit in it. There may be an electronics toker on here who could explain it better and maybe how to get around this as I've got 2 dimmers in my room going to waste. WWM

[BudMan]

Ive been doing some searching and theres mixed views on using these, some people on other grow forums seem to be using them, and others advise not to use them.... ???

Found this which i found interseting.. Not for me but good idea..

Bleed-off excessive airflow, using a mechanical valve

Controlling the fan speed may not be necessary. The airflow can be diverted mechanically as an option, in effect reducing the airflow without changing the fan's speed.

On the "out" pipe, one could put a y-split, with a flapper inside that can direct a fraction of the air to one half of the split (connected to your actual air circuit), and the remainder to the other (the "waste" air outlet).

Then, by adjusting the flapper's position, you could control the flow to your circuit, and dump the excess airflow.

[BudMan]

This here states that even cheap fan speed controllers kill your fan...

You cannot use a light dimmer to control a fan. There is a growing misconception that this is safe to do, but the logic behind it is flawed.

Let me explain:
A fan that has no speed control when manufactured has copper windings inside that determine speed and horsepower. These windings are fixed and unchangeable, and wired to be operated at a certain voltage, with a fixed amount of amp draw. I will explain how this works, but first I want to dispel the reasoning behind this misunderstanding.

1. Why do they sell fan controllers at hardware stores?

They are to replace the controllers that are already on a multi-speed fan.

2. I have heard of rheostat's being used to adjust the speed of a fan, why wont this work?

Rheostats, like potentiometers are glorified variable resistors. While they can be used to adjust the speed of a DC motor, its a big no-no on AC motors. AC motors need to run at preset voltage, motor speed, and current draw. It is a balanced system.

3. Can I use a thermostat to act as a rheostat?

NO. Thermostats are on/off switches that turn on/off at a desired temperature.

4. Can I use a rheostat if I also use some type of thermal protection device?

NO. Thermal devices fail too. Sometimes they trip for no reason, then your fan would be off when your on vacation and that can be disastrous for your crop.

5. What's the best way to run my fan at my desired speed?

There are 2 ways. First, buy a fan that runs at your desired speed. Second, you could purchase a variable frequency drive, but these usually cost more than the fan itself.

6. Why do ceiling fans have different speeds if you can't control speeds of an AC motor?

Multi speed motors have more than one set of windings. The speed knob on a fan is a switch that switches current to a different set of windings. Each set of windings are almost like a separate motor. They would each have their own parameters. Remember, the knob is a switch, not a speed controller.

Please do not invite disaster. Best case scenario, your replacing fans like they are going out of style. Worse case, burn your house down. It is not worth it.

* Now I will attempt to explain the science behind it all.

An electrical device operates when current runs thru it. When to much current goes thru it will burn up the device, wiring, etc... All devices have a resistance to current. The filament in a light bulb is a good example. A bulb has a fixed resistance. You can lower or raise the voltage but the resistance will stay the same. You would affect the current running thru it, which if you lower(as with dimming) there are no bad side effects. But increased current with shorten the life of the bulb, or burn it out immediately.

Wire has almost no resistance, which is why we use it to take our current to our devices. The inside of a motor is nothing but wire. But when you wind it in a series of coils (like inside a motor), you create a dense magnetic field when current is running thru it, casing the motor to spin, and do work. This is called inductive impedance, or sort of a magnetic resistance.

If you stopped a motor from spinning (like holding onto a fan blade), the motor would smoke, then burn up. Holding the fan blade eliminates the magnetic field and creates a rush of current. The same can be said of reducing the voltage across the fan with some sort of outside variable resistor. You are essentially weakening the magnetic resistance and allowing a current rush outside the operating parameters of the motor. This usually isn't as harsh as holding a fan blade, but it can be disastrous. At the very least, it would severely shorten the life of the motor.

There is currently only one way to control the speed of a single speed AC motor. Using a variable frequency drive. They do not change current, voltage, magnetic field, or any other factor other than frequency. U.S. power runs at 60Hz. Changing the Hz on the power supply to a motor will change the speed with little or no adverse effects. These drives, however, are not cost effective outside of an industrial environment. Fans are usually cheaper.

Do yourself a favor, buy the fan with the speed you want.

[whitewidman]

That would work but it does nothing to ease the strain on the fan and would increase fan noise, one of the advantages of buying a proper controler and over large fan is you run it much slower and quiter. And dimmer switches def don't work with ruck fans, I've tried and failed. WWM
Just noticed your new post above will read and digest.
Good post that. Yes that is what I've worked out by trial and error but what I said about controling noise still applies if you can afford the outlay.

[adsychat]

i broke 1 of my fans using it and it set me back another 10 quid lol

[dazed-n-confuzed]

My TT100 fan seems ok with this:

http://cgi.ebay.co.uk/ws/eBayISAPI.d...=STRK:MEWNX:IT

Although with the previous comments im worried I might kill it now! Before this I put a piece of card on the intake of the intake fan, covering the hole by about 50%, thus limiting the amount of air it could pull. Crude, but it worked

[fat freddy]

my rvk150 seems to be working fine with an ordinaray dimmer switch wired into it, theres a slight hum from the motor but nothing too loud! you need wiring infos?

[BudMan]

Exactally, seems to be working ok

The hum is the resistance in the fan motor freddy, reducing the life of your fan or even worse could cause a fire... Why you think proper fan speed controllers are so expensive? They step the voltage instead of causing resistance like your dimmer...

Also who said anything about wiring infos matey?

[Road_Runner]

I just bought one of these, was that a bad idea then?

http://cgi.ebay.co.uk/ws/eBayISAPI.d...m=120531561336