halogen desk light to LED conversion

[jason 77]

I just completed a LED project and thought I would share it on this site.

I had a friend give me a halogen desk light that didn't work anymore. After putzing around with it a bit I found that the power supply in the lamp was shot. So instead of buying a new power supply I decided to see if I could retrofit some leds in it. After taking out the old power supply bits I found a small 12 volt charger I had laying around.

As you can see the little guy only puts out 500mA, but this is more than enough for the leds I was going to use.

Next I took out the circuit from the charger and placed it on a perf board along with a simple constant current circuit set to 330mA. You can see this in the picture below, I had to move one of the capacitors to lie on it's side because it was too tall to fit in the base of the lamp. I also used the chunk of lead in the base to act as a sort of heatsink/mounting point for the mosfet in the constant current circuit.

Next I started on the actual LEDs, they are warm white 350mA 3.4 volt little guys and I used 3 of them. These are from the same batch I got off of ebay and used in my fishtank light retro, which I also posted on this forum a while back. I used a small heatsink from a old motherboard I had. As you can see in the picture below I put the leds in a triangle on the heat sink and managed to get it to fit where the halogen bulb was before. The 3 LEDs are wired in series and get 3.2 volts each and 330mA from the constant current circuit.

Here is a really bad picture of them lit up.. They are brighter than that in real life.

 

[biggerrigger]

Very nice DIY solution to a common problem. Keep up the good work. I too am working on a conversion with a bad transformer.

 

[rodfran]

Great LED fix! Thanks for the pics!

 

[foxtrot824]

Good thing there is a UV filter in place :crackup:

Nice mod.

 

[jeffosborne]

Well done, jason 77! I'll bet it is a great lamp to use now. I notice that you have incorporated a chipset heatsink under the LEDs, and that reminded me of the halogen light I modded for my son a while back:

These are neutral white Rebels, with the heatsink underneath epoxied to the metal cup bulb enclosure. This was also a 12 volt setup.

Cheers,
Jeff

 

[jason 77]

Hey Jeff, that looks like a great project as well! I have some rebel LEDs as well. I think you are the one that told me I could file off the contacts on the back of the LEDs so you could mount them as you have done in your picture. Do you have any pictures and/or explain to me how you did that? I don't want to mess mine up. Lol

And yes that is a heat sink from a chipset. I keep all the heat sinks from the old crap I take apart.

 

[jeffosborne]

jason, I do not file off the contacts on the bottom of the Rebel. I use a thin coat of standard-issue fingernail polish to isolate those contacts.

Note that I am careful to NOT cover the thermal pad directly under the LED dome. I do like it that the arctic alumina contacts not just the bottom, but also the sides of the LED, for best thermal conduction.

What do you have in mind for your Rebels?

Cheers,
Jeff O.