variable transformer for light

Does anyone make wall mount light dimmers of the variable transformer type (as opposed to the usual type of on-off current limiting)? it would not
need to support very many watts, so I would be hoping such a think could be made to fit in a standard wall switch box.
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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snipped-for-privacy@ipal.net wrote:

autoformers are made in all sizes http://www.variac.com/staco_Variable_Transformer_Map.htm .
however a product for this application would have to be well fused as the user could decide to screw in a large lamp and overload the device.
a solid state dimmer will be much less expensive and handle much larger loads for its size.
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| snipped-for-privacy@ipal.net wrote: |> Does anyone make wall mount light dimmers of the variable transformer |> type (as opposed to the usual type of on-off current limiting)? it |> would not need to support very many watts, so I would be hoping such |> a think could be made to fit in a standard wall switch box. |> | | autoformers are made in all sizes | http://www.variac.com/staco_Variable_Transformer_Map.htm . | | however a product for this application would have to be well fused as the | user could decide to screw in a large lamp and overload the device. | | a solid state dimmer will be much less expensive and handle much larger | loads for its size.
Do you know of any that have a true sine wave output?
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snipped-for-privacy@ipal.net wrote:

it would be pretty wasteful and expensive to use for example a 100W amplifier to power a light bulb.
while i have in the past run into cases where the RFI/EMI from a wall dimmer causes a buzz in audio equipment i find that most TRIAC dimmers these days employ zero crossover switching and RFI/EMI filters.
i dont know what you application is, however, you might find something here that you can adapt. http://www.littlite.com/main.php
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TimPerry wrote:

Do European controls on emissions (or is it power factor) that apply to switching power supplies also apply to triac dimmers?
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The new wave of sine wave output dimmers has taken a different approach, using the switch-mode technology widely used in devices as diverse as the ballasts of many discharge luminaires and the power supplies of virtually all computers and lighting consoles. There are few companies which work on sinewave dimming field.Dynalite has been shipping the SVC (Sinewave Voltage Converter) dimmer since 1998. Bytecraft VST (Variable Sinewave Technology) won an award at PLASA 98. Jands Electronics has announced the development of a prototype of its SWDim sine wave dimmer. The principle behind all of these sine wave dimmers is very simple: The incoming mains is switched on and off between 600 and 1,000 times per mains cycle (30-50kHz) with the on time (width) of each pulse being proportional to the required output power from the load, a method known as Pulse Width Modulation (PWM). The very finely chopped output is then filtered back into a continuous waveform through an inductor similar to the choke on a phase control dimmer, but very much smaller, as the pulse frequency is higher. The shape of the filtered output waveform is almost identical to the input waveform, only its amplitude is different, precisely what happens in a resistance dimmer.

How can a TRIAC dimmers employ zero crossover switching ? A triac dimmer in order to operate needs to turn the triac on in the middle of the mains phase to do dimming (and then keep conducting to next zero crossing). RFI/EMI filters can reduct the noise caused by the quitc turn on.
There are dimmers based on other semicondictors (power FETs etc.) that turn on ath the zero crossover and then more or less "slowly" turn off in the middle of the mains phase as needed. When properly implemented this type of dimmers cause less noise to mains then the old triac dimmers and need less filtering.

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wrote:
| How can a TRIAC dimmers employ zero crossover switching ? | A triac dimmer in order to operate needs to turn the triac | on in the middle of the mains phase to do dimming (and then | keep conducting to next zero crossing). RFI/EMI filters can | reduct the noise caused by the quitc turn on.
Maybe someone decided they didn't mind all the flickering and was happy to "count cycle" in a dimming process. I've never seen such a beast, fortunately.
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both triac dimmers and solid state relays should employ zero crossover switching (zero threshold detection). this insures the "glitch" at the zero point is minimized or eliminated.
here is a patent for one http://www.freepatentsonline.com/5734289.html
granted that as dimming is engaged, the waveform becomes non-sinusoidal.

apparently the problem is noisy lamps... maybe he could surround the bulb with Sonex :) (just kiddin')
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|> |> How can a TRIAC dimmers employ zero crossover switching ? | | both triac dimmers and solid state relays should employ zero crossover | switching (zero threshold detection). | this insures the "glitch" at the zero point is minimized or eliminated.
I also don't want the flicker that would be implied by only switching at the zero crossover.
| here is a patent for one http://www.freepatentsonline.com/5734289.html | | granted that as dimming is engaged, the waveform becomes non-sinusoidal.
It's the long rise or fall involved in switching either in or out at a designated point determined by the amount of time averaged current to let through that is the problem.
One method of solving this would be to chop up the waveform at a rate of 61.44 kHz with varying widths that approximate a sine wave times the desired output voltage or current, and smooth the end result back out to near sine wave with a capacitor or inductor.
Squeezing all that into a 1-gang box AND doing it in SERIES with the light could pose an interesting challenge. I assume it is difficult, but I asked around just in case one of the brighter engineers around actually has employment in the right job.
|> A triac dimmer in order to operate needs to turn the triac |> on in the middle of the mains phase to do dimming (and then |> keep conducting to next zero crossing). RFI/EMI filters can |> reduct the noise caused by the quitc turn on. |> |> There are dimmers based on other semicondictors (power FETs etc.) |> that turn on ath the zero crossover and then more or less |> "slowly" turn off in the middle of the mains phase as needed. |> When properly implemented this type of dimmers cause less |> noise to mains then the old triac dimmers and need less filtering. | | | apparently the problem is noisy lamps... maybe he could surround the bulb | with Sonex :) (just kiddin')
I've not yet done any of the math involved, and need to get some numbers to do the math anyway, but I might consider somehow wiring in a ballast intended for fluorescent just to get an inductor in series, and use a double throw switch to go one way for full and the other way for lower. Then I have to figure out level of low I really want out of it and hope the hum from the ballast isn't an issue (but it might be).
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| snipped-for-privacy@ipal.net wrote: |> On Sun, 8 Oct 2006 11:29:19 -0400 TimPerry
|>>> Does anyone make wall mount light dimmers of the variable |>>> transformer type (as opposed to the usual type of on-off current |>>> limiting)? it would not need to support very many watts, so I |>>> would be hoping such a think could be made to fit in a standard |>>> wall switch box. |>>> |>> |>> autoformers are made in all sizes |>> http://www.variac.com/staco_Variable_Transformer_Map.htm . |>> |>> however a product for this application would have to be well fused |>> as the user could decide to screw in a large lamp and overload the |>> device. |>> |>> a solid state dimmer will be much less expensive and handle much |>> larger loads for its size. |> |> Do you know of any that have a true sine wave output? |> | | it would be pretty wasteful and expensive to use for example a 100W | amplifier to power a light bulb. | | while i have in the past run into cases where the RFI/EMI from a wall dimmer | causes a buzz in audio equipment i find that most TRIAC dimmers these days | employ zero crossover switching and RFI/EMI filters. | | i dont know what you application is, however, you might find something here | that you can adapt. http://www.littlite.com/main.php
It's for a ceiling fixture. I want to eliminate the whining sound in the light bulb itself, which is there with solid state dimmers, presumably due to the chopping effect they use to limit current. I'd be happy to trade that high pitch for the low hum of a genuine transformer.
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snipped-for-privacy@ipal.net wrote:

you could rectify and filter the AC to DC after the dimmer. this would probably be best accomplished by using a step down transformer and 12 volt lamps or similar.
not to long ago i was at a speech given by the vice president. the ballrooms chandeliers were sending a highly objectionable hum into the podium mic. fortunately when the VP came out someone turned the lights up to full and the problem went away.
the trac lighting dimmers in my studios are not too bad. perhaps it the heavier filaments of the reflector type lamps that are used.
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| you could rectify and filter the AC to DC after the dimmer. this would | probably be best accomplished by using a step down transformer and 12 volt | lamps or similar.
An interesting idea.
| not to long ago i was at a speech given by the vice president. the ballrooms | chandeliers were sending a highly objectionable hum into the podium mic. | fortunately when the VP came out someone turned the lights up to full and | the problem went away. | | the trac lighting dimmers in my studios are not too bad. perhaps it the | heavier filaments of the reflector type lamps that are used.
In cases where the limited installation space is not an issue, I would go with a real variac transformer, or another solution that produces clean sine wave output.
In larger rooms, the color temperature issue could also be solved by having multiple smaller lights in clusters, and turning on as many in each cluster as needed.
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