# connect 2 3watt leds

Discussion in 'General Electronics Chat' started by conntaxman, Feb 7, 2010.

1. ### conntaxman Thread Starter New Member

Oct 30, 2009
12
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I found this on the net,How dose this look? and I hope that this will help out someone else,atleast some one built and showed a CIR. for the small project.
http://www.solorb.com/elect/solarcirc/2x3WLED/index.html
Now all I have to do is build 3 of these and run 6 of my 3watt leds for a ceiling light and see how it works out.
John

Apr 5, 2008
15,648
2,346
Hello,

It lokks rather odd. The heatsink is mounted next to the regulator instead of on the regulator.
The leds probably also need cooling, so the heatsink should also go under the leds somehow.

Greetings,
Bertus

3. ### andreapg Active Member

Feb 2, 2010
41
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This seems like a strange circuit.
I' ve never seen a simple led circuit using an heatsink, but all is possible...

Last edited: Feb 7, 2010
4. ### MikeML AAC Fanatic!

Oct 2, 2009
5,450
1,066
Electronically, the circuit will work well. If your input voltage is 12V, the total power dissipated by the resistor, LM317, and the two LEDs will be ~12W. All of that heat is going into the slab of copper-clad and the bent aluminum. Build one, and monitor the temperature rise. If you try to put it in an enclosure, that will block off air circulation to the heat sink, so you will have to verify that the temperature rise is within reason.

A suggestion: If you wired 6 LEDs in series with the LM317 current regulator, you could make that work by just raising the input voltage such that the voltage drop across the resistor and LM317 is still 1.25+~2.5V = 3.75V. Each LED would have it normal forward voltage of ~3.5V, for a total of 3.75+6*3.5 = 24.75V. Now the assembly would be dissipating ~25W, so you must use a big heatsink.

5. ### Wendy Moderator

Mar 24, 2008
20,766
2,536
One of the tricks I like to use is many resistors, such as 10Ω at ¼W. By using each at 1/8W in a network you can add up the power in small increments, and by buying the resistors in quantity you get them cheaply.

Welcome to the world of modern high power LEDs. These units will replace standard incandescent bulbs, I suspect his design is in the incandescent 40-60W range, but the LEDs are taking current around an amp or so. Since the LEDs drop around 3.6V they are actually dissipating 3W each, in real heat, so heatsinking is required. You'll note the case is designed for it too.

I like the construction myself, it seems pretty reasonable. My approach is to use really old CPU heatsinks, the kind before fans were needed.

6. ### conntaxman Thread Starter New Member

Oct 30, 2009
12
0
Mikelm. But the leds will be fed with 12vdc.Battary.I said that and what I wanted to do. Do you have a Cir. of something that I could use?If so post it.That would also help others.
Tks
John

7. ### MikeML AAC Fanatic!

Oct 2, 2009
5,450
1,066
If you said it, I missed it. If you are starting from a 12V battery, the voltage variation is only 12.6 to ~11.8V, so you dont need the LM317; just an appropriately sized resistor in series with three LEDs.

Last edited: Feb 8, 2010

Feb 2, 2010
41
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