Dimmers w/halogen bulbs


Client wants to install some low-voltage halogens with a dimmer. Is this OK? I know the dimmer will work, since the lamps are a resistive load, but I'm not sure the halogens want to work on reduced voltage. Anyone know for sure?
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David Nebenzahl spake thus:

Doh! What was I thinking? *Not* a resistive load (transformer, remember?) Never mind.
(Although I have successfully used ordinary dimmers with transformers for some of my own projects, like a homebrew resistance soldering unit, I'd never install one in anyone else's house.)
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David Nebenzahl wrote:

You can dim low-voltage halogens, but I am not sure the standard over the counter dimmer would be the best best, it will depend on your power supply. However I suggest you consider the effect on a "halogen" lamp when it is dimmed. After all they are designed to last longer using the halogen cycle and that requires high heat. At any dimmed setting, the lamps are likely not to go into a halogen cycle so the life expectancy may be cut short.
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I have had many customers who chose low voltage lights become unhappy when they decide to install dimmers. There is always a noise problem. Even with a dimmer that is rated for magnetic or electronic power supplies there is still some noise present depending on the light level. If they want to dim the lights, don't use low voltage or install multiple switches to shut off different areas to give a reduced light look.
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I agree, if you want to dim them be sure to at least use electronic or magnetic low voltage dimmers

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Not a problem. There are a couple of things to know, however:
- Use the proper dimmer. Low voltage halogens require either a transformer or electronic voltage reducer. Use a dimmer that's compatible with what you're using.
- Halogens don't care if they are dimmed. At full power halogen lamps are designed to utilize a tungsten recycling process which keeps the inside of the bulb clean. The gas chemistry inside the bulb recycles the tungsten that would ordinarily deposit on the bulb surface back onto the filament. If you dim the lamp, the halogen cycle stops; but that's O.K. The filament is operating at a lower temperature and not throwing off much tungsten anyway. Some wonder if there is some kind of "forbidden zone" of operation -- a dimmer setting where there is still filament evaporation, but where the halogen cycle is not operating so the bulb darkens and perhaps fails. According to the lamp engineers that I've talked to, that's possible, but not likely in general lighting lamps. But if it should happen, (you will be able to see the filament tube with a black deposit on the inside surface) simply operate the lamp at full power for a few minutes to restart the halogen cycle.
I have a house with several dimmer-controlled track lighting systems which use numerous 120 volt PAR20 and 12 volt MR16 halogen lamps for downlighting, accent lighting, etc. These systems are operated 6-10 hours/day at various dimmer settings. I used transformer-powered fixtures for the MR16 lamps. There is no noticeable noise, even when the dimmers are at the lowest setting, unless the house is absolutely quiet (not a normal situation). I've not had any 12 volt MR16 lamps fail during the 3+ years that the system has been installed. The lamps have a life rating of 5000 or 6000 hours, so I'm starting to expect a few failures.
The 120 volt PAR20 halogen lamps are very sensitive to physical shock. I've had those fail when I simply adjust the fixture and happen to shake the fixture. What happens is that some filament coils short together and put too much voltage on the rest of the filament. (you can see the filament move when you look at the light beam). Now, I dim the lamp and move the fixture very carefully and replace lamps with the power off.
TKM
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SPEAKING OF dimmers........................when will they work with the new florescent lights?
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readandpostrosie wrote:

Depends on the dimmer and the lamp.
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readandpostrosie spake thus:

Good question. So far as I know, that would require a complete redesign of the electronics which drive the lamps, which now require a sufficient voltage to operate at all. Theoretically possible, just depends on economic factors.
BTW, speaking of compact fluorescents, what are they going for in your locale? Here (S.F. Bay Area), cheap bulbs pop up from time to time at various places, subsidized by the local greedy monopoly^H^H^H^H^Hutility company, PG&E. Currently, Al Lasher's Electronics in Berkeley is selling the nice bright 23 watt "twisted" lamps (100 watt equivalent light output) for $1.25 each. The next best deal seems to be at Home Despot, which is selling 4-packs of the same bulbs for about $10.
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David Nebenzahl wrote:

Some CFLs are rated to be dimmed, most are not. Read the packaging int the store. Usually, the dimmable CFLs are a little more pricey.
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Many of the low voltage halogen lights us an "electronic" transformer. It is actually an electronic power supply running a transformer at a higher frequency than 60Hz ... the higher the frequency, the less iron needed in the transformer, making it smaller and lighter. Some of these may be dimmed, some not. You have to check the specs on the unit. Also, you probably need a dimmer which can be used for this application, as the load seen by the dimmer, is not purely a lamp filament. BTW, I have 2 strings of 20 watt hockey puck lights running from 2 electronic transformers and dimmed by an electronic dimmer with no problems. Both dimmer and "transformers" were rated for each other.
TKM wrote:

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Our track lighting uses a special dimmer designed for this purpose. Additionally it uses a high tech transformer (essentially converts line input to high frequency so it can use a smaller transformer). I just went to a lighting store and they sold me the appropriate stuff. NOT CHEAP but lights etc were what the wife wanted.

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Well said TKM!
Dimmer quality is big factor in the noise issue as well. (So many myths, so little time...)
Richard Reid, LC
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