120V Halogen dimmer!

[RobertRoss]

Hi,

Im a robotics specialist by day which likes to dabble in electronics and CPUs by night. Most of my spare time is put in assembly and C++ programming languages for microprocessors... a big passion of mine! However, electronics intregues very much, however aint no expert due to lack of time.

I am really impressed of such a website where electronic questions can be posted, I just discovered this site this week and this is my 2nd question and by which I deeply thank the guys that answered the first one. My first question was to get a schematic for a 120VAC incandecent dimmer. And I did get one. I really enjoyed looking it over, reading up on it and understanding it. Anyway here is my 2nd question.

I would love to construct a light dimmer which can dim incandecent and halogen lamps. Usually halogen lamps work on 12VAC, so when you supply the 120V, thier usually hooked up to a 120VAC/24VAC transformer.

That being said!... My dilema is that I don't know the principles for a halogen dimmer. You see, I understood the principles of the incandecent one (Firing of triac, phase angle, threshold voltage in the diac which is connected to the gate and soforth....) but are these principles the same for a holagen fixture (Halogen lamp with transformer).

If anyone knows this, I would greatly appreciate an electronic schematic for the holagen dimmer, which basically, the dimmer would have to dim the trasnformer ofcourse since halogens need a transformer.

The idea of me wanting to construct a double function dimmer (For incandecent and halogen lighting) the schematic I would be ultimately looking for would have to be able to dim both lighting mediums. If this is too complicated, I would appreciate any link or reference that could lead to my answer.

Maybe this dimmer will eventually be able to dim fluorecent fixtures also, but thats next year's question!!!!!!!!

Hope I am not to demanding! Thanking all of you in advance once again.

Best regards
Robert

 

[stevez]

Does your 'halogen' light bulb have a filament? If it does then the light dimmer for any normal incandescant light will work as long as it's the right voltage, power, etc. If your 'halogen' light bulb is really an HID, High Intensity Discharge, then it won't work (which is what you suspect).

An HID lamp provides light as a result of an arc heating the gas inside the bulb. Incandescant light bulb provide light as a result of a conductive filament that gets hot when current flows. Typically the arc in an HID bulb is started with a momentary high voltage pulse and once the gas is heated the arc can be maintained at a lower voltage. The lighting system on my truck is fairly common - the arc runs at 85 vdc and is started with 1,000 volt pulses.

There is a range of voltages for the arc and if I am not mistaken, increasing the voltage will increase the light output. Reducing the voltage will decrease the output but at some point the arc cannot be maintained and the light will go out. My partner here in the office makes commercial lighting one of his specialties and said that a 50% reduction is about all you can expect. He was just given a brochure from the American General Energy Corp on their "LightBoss" HID dimming system. I understood from the discussion that special ballasts (the power supply on each light fixture) were required for this to work.

The power supply for the lighting system on my truck is probably no different than the solid state supplies for Low Pressure Sodium, High Pressure Sodium or other non-filament lighting systems except that the input is 12 vdc rather than a much higher ac voltage. It appears to be a switching type supply with a control system that delivers the 1 kv starting pulses and maintains the 85 vdc.

From what I've managed to learn about this type of light I'd suspect that you'd have to understand the bulb and power supplies (ballasts) then decide how to proceed from there. Simply lowering the voltage supplied to the fixture may not work - if the ballast has an internal regulating system it will fight any attempt at voltage reduction.

I learned quite a bit about HID systems by doing some web searches on automotive systems. There's a lot of very confusing and incorrect use of terms. Some of the incorrectness is deliberate - to convince potential purchasers to purchase immitation HID lights - so be ware of that stuff.

You might see if you can get some discarded HID fixtures from an electrician or automotive junkyard to see what's inside.

Good luck.