Electrical items and dimmer switches

A two part question, first of all: Is it possible to connect a dimmer switch (usually used on light switches) to any wall socket thus replacing the normal switch next to the plug with a dimmer?

Secondly: What would happen if you were to do such a thing? Taking the example of a TV what would happen as you gradually increased the “power” going to the set from zero up to maximum? Assuming in this case that the T.V. could be left switched on when disconnected from the power so it would switch back on as soon as enough power were supplied to it. At what stage would you begin to see the picture and hear the sound and how would it differ from normal usage?

To your first question, yes it is possible. I’m not sure if electrical code permits it or not, but I would guess not.

For your second question, a dimmer will work fine for lights and simple motors, but anything electronic that expects a constant voltage such as a TV, computer, stereo and most other appliances would be damaged or destroyed.

Dimmers do not work by lowering the supplied voltage, they work by reducing the time during the AC cycle that the juice is ‘turned on’. Trying to run anything other than normal indcandescent lights off a dimmer will likely end in tears, if not flames.

mittu if you tried turning on your TV gradually as you describe it might flicker into life at some point where it is getting just enough power but you’d probably get horrible interference from the nasty/spiky power supply waveform. The problem FatBaldGuy isn’t with a ‘constant voltage’ – the power supply in your PC/stereo will struggle manfully to keep the internal supply smooth, the trouble is that 1)There may not be enough juice getting through to keep the power supply capacitors charged (bad) 2) You are will be bombarding the device with RF spikes right into the power supply, the PC in particular may not like this.

I think running an inductive load (anything with a motor) off a dimmer might get you a Darwin. I’m gonna Google on this I’ll let you know if I turn anything up.

As mentioned by Small Clanger, all conventional light dimmers using something called a “phase-fired proportional control circuit” to control the RMS voltage to the load. It’s not the only method that could be used, but it remains popular because it is energy efficient and the hardware is small, light, and very cheap. The drawback is that the resulting waveform looks like crap, i.e. instead of being a nice, smooth sine wave, the waveform contains lots of sharp transitions. The sharp transitions have lots high-frequency components. This can be a problem with certain loads, as many will convert the high-frequency energy to heat. One example is a transformer, which is found in many devices.

Ceiling fan manuals routinely advise against having the motor on a circuit controlled by a dimmer switch. The lights are okay, just not the motor.

I know that X10 fan controls are available. I’ve always wondered how they differ. Maybe AM modulation?

I’m not sure, but I think it’s some kind of PWM scheme. At any rate, I’ve heard X10 fan speed controllers aren’t all that great, as the waveform has a tendency to make the fan motor hum, especially at slow speeds.

Here’s a neat fan speed control circuit that interfaces with an X10 controller. The author claims it will not make the fan motor hum.

I now have a new project for the summer. Various devices in a plexiglass “bomb box” with an external dimmer switch. I’ll make sure to have the video camera set up. Should I start with an old TV from Goodwill or something with an internal motor?

I have a small ‘rotating light’ that I run off a dimmer. As I turn it on the motor goes from an annoyed rum, to a slow rotation, to it’s normal speed though I don’t usually spend much time between ‘fully-on’ and ‘totally off’. It’s more or less a single flashing siren light [minus the sound] like those found on emergency vehicles. So far I’ve had no problems though I suppose I might be messing up the motor.

Given that it’s a small, relatively weak motor and the thing was free I’m not too worried. Currently it’s just a neat thing to turn on every once in awhile.

Article 404.14(E) of the 2005 NEC: Dimmer Switches. General-use dimmer switches shall be used only to control permanently installed incandescent luminaires (lighting fixtures) unless listed for the control of other loads and installed accordingly.

So, a fan speed controller may be installed to serve that purpose, a dimmer for dimmable fluorescent ballasts could be fitted, but using a dimmer to control a duplex receptacle would be a code violation, IMO.

That’s what we need asterion, someone prepared to risk life, limb and electrical devices in the fight against ignorance!

Hey, I’m the guy who thinks it’d be cool to get an old computer monitor or something and run the equivalent of a lightning strike through it just to see what happens. I’m also the guy who wants to see 10% Pd/C ignite by being dropped through too much air. Both a professor and a student have managed to do it this semester and I wasn’t in the lab either time. :frown:

As danceswithcatssaid, a standard dimmer won’t work with fluorescent lights. They can be dimmed, but it’s tricky. The start-up requires full current, so dimming has to be wired from inside the fixture. Consult a lighting dealer or an electrician.

TVs and monitors only work within a fairly narrow range of power. Some devices, such as my Carver stereo receiver, “see” weird voltage as bad data, and they shut down. They have to be unplugged to reset.