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Archive for October 5th, 2018

Halogen Desk Lamp Conversion: Preliminaries

A discarded 20 W halogen desk lamp arrived in the Basement Laboratory for rebuilding:

Halogen Desk Lamp - head layout

Halogen Desk Lamp – head layout

An incandescent bulb doesn’t care about AC or DC, so a simple transformer also serves as a counterweight in the base:

Halogen Desk Lamp - 12 V 20 W transformer

Halogen Desk Lamp – 12 V 20 W transformer

I might replace it with some steel sheets, although I have no immediate need for a bare transformer.

A case adds 19¢ to each 10 W 300 mA LED driver:

Halogen Desk Lamp - 10 W LED driver innards

Halogen Desk Lamp – 10 W LED driver innards

Nice strain relief on those line-voltage wires, eh?

A simple test setup with three 3 W COB LED panels:

Halogen Desk Lamp - 3x3W COB LED test

Halogen Desk Lamp – 3x3W COB LED test

I clamped them to the aluminum sheet for heatsinking before I lit ’em up. The circles traced directly from the lamp’s hardware give some idea of the eventual layout.

I have more-intense LEDs, but spreading the light over a larger area should work better for the intended purpose. These are pleasant warm-white LEDs, too.

The fourth LED raised the forward voltage beyond the supply’s 42 V maximum, causing the supply to blink on and off.

Much to my surprise, the driver has plenty of 60 Hz ripple:

COB LED 3x3W - 10 W driver - 100 mA-div 10 V-div

COB LED 3x3W – 10 W driver – 100 mA-div 10 V-div

The top trace averages 280 mA and the bottom trace 32 V, so the LEDs run at 9 W = 3 W apiece, as they should.

Now, for some metalworking …

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