LED Lamp Conversion

http://www.greenledlamp.info This project shows you how to convert a halogen desk lamp into a high efficiency LED lamp. The full project is on greenledlamp.info .The converted lamp can be powered using a AC/DC wall adapter or directly from a 12 volt solar source or other alternative power source. It is easy to build but does require some basic electronic skills.

Step 1 Circuit Design

This step shows you how to build the lamp circuit. For more details and circuit theory goto http://www.greenledlamp.info. I used a 12 volt 500mA DC adapter, 3.2volt 20mA/100mA white discrete LEDs, 100 ohm 1/4 watt resistors (8) and 33 ohm 2 watt resistors (2), female DC jack.

The LED array connects 24 LEDs into 8 parallel rows. Each row contains three LEDs and a 100 ohm resistor. The two 33 ohm resitors are connected paralle resulting in 16.5 ohms in series with the LED array.

Comments

[lemonie]

and greenwatts.info ?

[helpmonkey]

also my site :0)

[d-lite]

You seem to have copied the .info website here... What's the story? Also, the website claim a consumption of 2.5W but 24 LEDs, using your numbers of (3.2v @ .02amp) accounts for only 1.5W. So the circuit is wasting 40% of its power heating up the adapter and resistors?

[helpmonkey]

there is about 1.5watts consumed by the LEDs, another half a watt consummed by the eight 100 ohm resitors and another half watt by the compensating resistor... but that was as good as I could get it with the available components as I did not want to buy anything... another option is to simply remove the two 33 ohm resistors and use a lower voltage dc adapter.

[qs]

Have you tried replacing the 100ohm with another LED? If you have 12.8v from your adapter, which is very likely, then you'd get 25% more light and save yourself the hassle of destroying circuit boards for their resistors! I'd start and measure the voltage across the wall-wart, then the LEDs. Chances are you can just use another LED to drop the voltage you are currently burning up in the resistor and have all 4 LEDs running with about the same brightness. Now THAT is being green!

[helpmonkey]

yes I did copie the website as it is my website ... the circuit is wasting some power but its is entriely made from recycled components ... couldnt find 120 ohm resistors...

[Nerdz]

True, 120 might be hard to find, but if you could get 100 Ohm and find a 20 ohm to 50 resistor, it would put you where you need to be. OR if you had a Load (and I do mean like 100+) 100 ohm resistors, you can put two in parallel to make a 50 ohm resistor, add that in series with a 100 ohm resistor, and you'll have a total of 150 Ohms. I

[helpmonkey]

good idea but it would make the LED array assembly rather difficult

[d-lite]

We used to 'shave' our resistors - let's say I need a 120 and had only a 100, I'd take an xacto knife and nick the 100 to just under the enamel. With a little bit of practice, we can get anything up to 200ohms from the 100's.

[lemonie]

What is your connection with greenledlamp.info? L

[helpmonkey]

hi both sites are mine

[Nerdz]

I do mean to criticize here, but you can get rid of the resistor thats in series with the whole circuit. Since your want only 20mA to get to the LEDs, you can calculate the resistor using ohms law. Since the resistor is going to have a voltage drop of 2.4v, you would need a 120 Ohm resistor (2.4v/20mA). Closest standard value is probably 140, Which would still be OK! Less current would get to the LED, but in my experience, unless your reducing the current by something drastic Like 15mA) a 5mA difference in current doesnt make a difference in brightness. Less current also means less power being wasted in the resistor. Also, power adapters are rated for that load. If your adapter is 12V @500mA, That means it will be 12V when you connect a load of 500mA on it. I have a feeling the 2.5W is a typo. Theres no WAY a transformer can waste that much heat. Their 95% to 99% efficient.

[d-lite]

It'll be close: About 0.5W is burned up just in the resistors, and the efficiency of a 500mA transformer running at 160mA cannot be that great.

[helpmonkey]

try to find 120ohm reisitors on scrap circuit boards ... not very easy ... 100ohm is much mor common on power supply boards ... I might have miscalculated the watts i will check .. thanks for the comment