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Old 25th June 2003, 01:10 PM   #1
dorkus is offline dorkus  United States
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Default feeding AC halogen light bulbs DC?

hi all,

so, i bought these low-wattage lighting fixtures at Ikea that i want to install around my room for mood lighting, for late-night listening and movie watching (among other things.....). the bulbs are rated at 12VAC, 20W, and are fed by a 12V 1600mA transformer.

i want to ditch the stock transformers because they're annoying wall warts, and also because i have a few of these lights and don't want to use so many transformers. i also want to create a remote switch/dimmer control. i could use one of those cheap SCR-type dimmers but they create a lot of noise. so one thought is to just build a regulated variable DC supply for the bulbs... overkill, but it takes care of the noise. could i feed these bulbs DC though, or will they blow out? also, any cheaper/easier way to dim them w/o the expense of a regulated supply?
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Old 25th June 2003, 07:54 PM   #2
dhaen is offline dhaen  Europe
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Default Think heat...

Hi,

To achieve what you want with linear regulators, you'll need heatsinks like a Pass amplifier.

You can buy dimmable electronic "transformers" for low voltage lights. They sometimes need a different type of dimmer though.

I'm afraid all electronic "transformers" are noisy.
You can use normal 12 volt toroids, but make the loading just right, so that the voltage isn't too high. Otherwise the lamp life will be seriously shortened.
You can also buy dimmers suitable for feeding inductive loads (real transformers).

Cheers,

Afterthought: Build a really powerful amp and run the lights from that! Fed with a sinewave, the volume control becomes the dimmer
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Old 25th June 2003, 08:04 PM   #3
dorkus is offline dorkus  United States
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Default Re: Think heat...

Quote:
Originally posted by dhaen
Afterthought: Build a really powerful amp and run the lights from that! Fed with a sinewave, the volume control becomes the dimmer
hehe, yeah sure!
actually, the amp wouldn't have to be that powerful... 12V @1600mA comes out to what, around 8 ohms? 20 watts into an 8 ohm (resistive?) load, that's not so bad...

hm, there has got to be some sort of solid-state device these days that can deal with this w/a minimum of heat/power loss and no noise... if not, i'd probably have to use a variac or something of the sort, or use one of the noisy solutions and add some filtering to keep the noise from reaching the AC mains.
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Old 25th June 2003, 08:17 PM   #4
dhaen is offline dhaen  Europe
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Default Re: Re: Think heat...

Quote:
Originally posted by dorkus


hehe, yeah sure!
actually, the amp wouldn't have to be that powerful... 12V @1600mA comes out to what, around 8 ohms? 20 watts into an 8 ohm (resistive?) load, that's not so bad... ..snip..
But that's just for 1 lamp! Those lamps don't light much area, you normally need quite a number. In my kitchen I have 11 50watt LV lamps.

Cheers,
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Old 25th June 2003, 08:21 PM   #5
dorkus is offline dorkus  United States
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hm, true. i bought 3 lamps, which should be enough to go behind my tv and stereo... just background lighting. how do you power your 11 kitchen lamps? do you have one big transformer?
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Old 25th June 2003, 08:28 PM   #6
dhaen is offline dhaen  Europe
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I have 1 electronic transformer per lamp. They live in the space above the celing. This is not ideal, as the temperature is quite high. They only seem to last a year or 2.
Did you know that LV lamps use dichoric reflectors? They are designed to reflect the optical energy, but pass (to the rear) the infra red. Anyway, that's why it's so damn hot up there!

Cheers,
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