Thursday, January 02, 2014

work light led retrofit

My portable work light until recently used a 500 watt quartz halogen bulb. That was dangerous because it got hot enough to burn.

Now it is an LED light which uses only 10 watts and barely gets warm while throwing lots of light.

I have retrofitted the light to use two 10 watt warm white LEDs. The LEDs run at half their maximum power from a reclaimed printer power supply which now hangs underneath the light. The LEDs get DC from AC via the power supply. Not as bright as with the halogen bulb but plenty bright enough for most situations where it will be needed.

Because of the low power consumption and the low heat produced, I think it is much, much safer than before.

The cost of parts for my conversion was about $6 ($3 for the two LEDs on Ebay from China and about $3 for a used HP printer power supply at the local recycling center, also a bit of aluminum sheet and bar and a few tie wraps and screws, possibly another dollar?). It took a pleasant evening to sort out the method and to do the conversion.

Unfortunately, I did not take a "before" picture. The light that you start with might be different from mine but I think these were very popular five, ten years ago? This is a general guide. Some of my other relevant work with LEDs has links.

The first step in my retrofit was to remove the halogen lamp and its supports and contacts as well as all the high voltage (117VAC) mains wiring from the housing. The parabolic reflector and a mounting bracket were the only parts saved.

This is the halogen lamp and its porcelain supports and contacts, now discarded. (click on any picture to enlarge it)

This pic shows the two LEDs mounted on the reflector. Note that the existing reflector was used as a part of the heatsink.

Another view of the reflector showing the sandwich of two aluminum bars and aluminum sheet with the reflector. The small screws hold the sandwich together and hold the LEDs firmly to the heatsink.

This is how it goes together. The technique is similar to what I am doing with the diy garden lamp. The 1 inch aluminum bars acts as a heat spreader from the LEDs to the aluminum sheet and the existing reflector which provide a large surface area.

I laid out the holes on one bar, drilled them carefully and then used a punch to transfer the hole positions to the other bar. I drilled the second bar and the center hole in both and then used a medium sized bolt through the center hole to clamp everything together to drill the small holes through the existing reflector and the aluminum sheet.

Not shown in the diagram is the heat sink thermal compound which is applied in a thin layer between the parts as they go together. In this closeup, you can see the thermal compound at the top edge of the aluminum bar as well as the mounting and the wiring of the LEDs.

I am using a reclaimed HP printer power supply rated at 18 volts DC at 2 amps. I wire the LEDs in series so that each receives about half the total, or about 9 volts. At this voltage, the LEDs will conduct about 350mA so the power supply has much more capacity than is required. The power supply stays cool.

This is the spreadsheet with the test results I got for the particular LEDs that I am using. The LED tests are described here

This picture is taken auto no flash with my Canon G15. There is no other lighting except for the LED work light. I have found that it is challenging to show you lighting results, but I think that this picture is pretty accurate.

Thank you for your interest in my work.

Please see my other lighting projects at the tab above.

George Plhak


Home Led Lighting said...

This is a great inspiring Post. I am pretty much pleased with your good work. You put really very helpful information. Keep it up. Keep blogging.

Anonymous said...

good job!
I'm "hot" on your trail for all the same reasons - energy and too hot with halogen.