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Joined: Mar 2005
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Knowing full well that dimmers and CFLs don't mix, I tried one on our 13-lamp chandalier because, well, 13x40W is a lot more electricity than 13x15W for less light and I wanted to convince my wife we should be using CFLs, which she normally hates. Also, it's a cheap 6 for $10 wal-mart CFL so I didn't mind if it burnt out in a week as has been my experience with our other dimmer and the occupancy sensor in the den.

Inexplicably, it's not only worked, but worked GREAT. 12x40W incandescents with 1x15W CFL- the CFL is brighter, dims better, consumes less electricity, and has lasted over a year now. With the dimmer the whole way down, the incandescents are useless, but the CFL is giving off a niec bright glow still. And it gives much better color of light (it's got these faux candle covers that normally makes the room look orange.) I'm hesitant to try it with more than one CFL without yanking the dimmer, especially now that I've actually looked at the circuit and what I did here, but it really does surprise me.

Last edited by SteveFehr; 05/06/08 06:51 AM.
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British Gas, (a major retailer of electric power, - due to the UK "free market"), is presently advertising that it is about to deliver four CFLs to each of its customers.
Who knows what make or type these may turn out to be, or whether anyone will read any instructions before using them.
That could stoke the flames a bit!
I'm actually with BG, so I'll report back when mine arrive, if this thread is still running.

Joined: Jul 2007
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Be careful though. Just because it works does not mean it is safe. You can put a fire out with gasoline but...

It is like call a DYI'er an electrician. "hey it works. What the problem?"

Last edited by sparkyinak; 05/07/08 11:38 AM.

"Live Awesome!" - Kevin Carosa
Joined: Jun 2007
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I've taken apart a CFL and they contain a rather crude switching power supply.

Three things or combination of things could be happening:
Capacitor is shunting excessive harmonics
Main switching transistor is overburdened
Main rectifier is overburdened with the harmonics (cheap ones cannot handle much more than 100Hz)

Switching PSUs will attempt to maintain output regardless of input...and dumb ones do it until the switcher fails due to high current! Such failures are often violent with the transistor actually exploding and leaving in some cases just some half melted leads on a scorched board!

The above poster is correct, filtering the harmonics will not work unless the power supply is designed to properly respond to a low supply voltage. It will still fail, it might take longer to fail, but I'd be surprised if it lasted longer than a day or so.

All of these potential failure modes could be prevented by simply adding a thermal fuse and then mounting it to the main switching transistor. Since the thermal fuse will also blow if subjected to excessive current, you can protect against the diode and cap failure mode too as they will typically fail shorted and pop the fuse.

Joined: Jun 2006
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Two related notes:
At the theatre I work for we use CFL's for the house lights on an old CD80 Strand dimmer rack (well, used to, the Iowa floods killed the rack and the switchboard). They dim quite nicely, minus the minimum dimming percent (cathode heating). We plan to flip them out, once we get back into the building full time, as the old R-40's burn out. For those that don't work with them, the Strand rack is a semi-standard wave-chopping dimmer system.
An odd use I found for dimming a non-dim is breaker locating. In the same building as above we have WAY too many panels (it was built in 1928 and remodeled four times). I needed to find a breaker to switch out two dead dimmers with three-way switches. I found the breaker by dimming the CFL's, which caused the panel to hum. Once I found the panel I killed breakers until the lights died. (I obviously verified no power before I worked on it, I don't trust this building).

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The reason that dimmers don't work with CFL's is because of the way they modify the phase angle of the input voltage.

Having said that, a standard fluorescent lamp requires a strike initially to get the gas in the tube to ion-ise.
This takes a bit of current to achieve, more than what a light dimmer made for incandescent lamps can provide, this can kill a dimmer, especially if set low when first switched on.

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