[ricklach]

I have 30-3W LED puck lights that are configured for 110V input that provides a 3-12V DC output. I want to use these lights for accent lighting in cabinets but the 3W output is way too bright. In the existing cabinets are LEDs that are much lower Power (say 1/8W) that are all run with an 12V DC power supply - all the lights are configured in a parallel circuit. I want to replace these lights with the 3W lights but at a much lower power consumption (say 1/2-1 W).

I snipped off the 110V driver/dc converter from one of the lights and using an old computer power supply, connected the leads to the 3.3V, 5V, and 12V DC outputs from the power supply. The light turned to full power at 12V, but did not light at either of the other two voltages. I reasoned that at 3.3V it would turn on the light but at a much less intensity.

So the question is: can I get these 3W lights to illuminate at something less than the 3W output by using either 3.3 or 5V from the computer power supply, or use the existing power supply and reduce the voltage by adding a resistor to the + side of each light. Bottom line, I want to connect all 30 lights in a parallel circuit using 3.3, 5, or 12V but reduce the light output (lumens) to something lower than the rated 3W (ie.1/2 to 1 W).

[donf]

First, when you do what you are attempting to do, you violate the design of the product and move outside of the product test environment used by UL prior to listing the product.

That said, using Ohm's Law, you 30W / 12vdc lamp uses roughly 2.5 amps and is roughly 4.8 Ohms of resistance. Since the resistance of the lamp will not change you will have to get a power supply that will give you 12 vdc @ 0.0025 amps output in order to generate .05 Watts.

I suspect that you will not have enough amperage to excite the lamp much less get it to give off any illumination.

[talaniman]

Seems much easier to use smaller wattage 3 way light bulbs.

[ricklach]

I believe the solution to the problem, which both respondents failed to interpret correctly (ie. thirty - 3 watt lamps not one 30 watt lamp), is a constant current/voltage power supply. The 3w lamps are probably wired in series and a test with a 9v battery proved this. So you need a minimum of about 9V to excite the lamp. To dim the lights use a dimmer. The constant current/voltage power supply should accept a variable voltage input (e.g. 70-220 v) and provide a variable output current and voltage in the 3-12 v range. Case closed.

[hfcarson]

Brilliant!