Halogen Desk Lamp Conversion

As part of converting the halogen desk lamp to LEDs, I replaced the hulking iron transformer with a flatter counterweight:

Halogen Desk Lamp - 12 V 20 W transformer

Halogen Desk Lamp – 12 V 20 W transformer

Under normal circumstances, you’d use something like steel or lead sheets, but Tiny Bandsaw™ can’t cut any appreciable thickness of steel and I gave away my entire lead stockpile, so I sawed disks from a pile of non-stick pancake griddles and drilled suitable mounting holes:

Parallel clamps in action

Parallel clamps in action

Another disk (from a formal aluminum sheet!) goes into the lamp head, with a trio of 3W COB LEDs epoxied in place:

Ex-Halogen Desk Lamp - 3x3W COB LED assembly

Ex-Halogen Desk Lamp – 3x3W COB LED assembly

The other side of the disk sports a heatsink harvested from a PC, also epoxied in place:

Ex-halogen Desk Lamp - heatsink fitting

Ex-halogen Desk Lamp – heatsink fitting

Realizing the head required only a little filing to accommodate the heatsink sealed both their fates.

A test firing showed the heatsink needed more airflow, which didn’t come as much of a surprise, so I milled slots in the lamp head:

Ex-halogen Desk Lamp - vent slot milling

Ex-halogen Desk Lamp – vent slot milling

Deburring the holes, blackening the sides with a Sharpie, and tucking a bit of black window screen behind the opening made the vents look entirely professional.

The small dome in the base originally cleared the transformer and now holds the entire 10 W LED driver, along with all the wiring, atop the counterweight sheets:

Ex-halogen Desk Lamp - base wiring

Ex-halogen Desk Lamp – base wiring

A cork pad covers the base for a bit of non-skid action:

Ex-halogen Desk Lamp - cork pad

Ex-halogen Desk Lamp – cork pad

I couldn’t convince myself filling in those sectors would improve anything, so I didn’t.

And then It Just Worked:

Ex-halogen Desk Lamp - in use

Ex-halogen Desk Lamp – in use

All without a trace of solid modeling or G-Code …


  1. #1 by Vedran on 2018-12-10 - 15:46

    I actually tried almost the same thing a while ago, but I decided that even just two 3W emitters were running too hot – even undervolted to something like 9.5V. Heatsink was old CPU unit, maybe 60x60x45mm with chopped off corners to fit inside the heavily perforated lamp cone.
    How hot are you running?

    • #2 by Ed on 2018-12-10 - 18:18

      It’s on the uncomfortable side of warm, with the LEDs 60 °C above ambient, but there’s no easy way to grab them, the plastic case runs barely 10 °C over ambient, and the heatsink is well recessed.

      Even I’m not worried!

  2. #3 by Vedran on 2018-12-11 - 13:22

    Running 60C above ambient means they might not last very long. I needed it for a non-technical person and also had a very strong desire that it never comes back to my shop :)

    Apparently new LED TVs suffer from a same problem. My friend that makes a living servicing electronics says they run the backlight hard enough that emitters mostly fail open after about 5 years. This took me by surprise – I assumed LED backlights were running cool and the failure mode would be low brightness after many years.

    • #4 by Ed on 2018-12-12 - 09:41

      An 18 W / 1 A industrial-strength emitter followed me home from Squidwrench yesterday, so I’ll eventually rehabilitate another desk light. It’s such a concentrated source I must mount it shining into the reflector, rather than directly toward the desk, to prevent harsh shadows.

      So many projects! [grin]