More undercabinet lights

October 19, 2008

I saw an article in today’s Boston Globe on wind power at Block Island. They pay 65 cents per kilowatt hour there. We pay 17, and I thought that was high. Seems like these guys would be likely customers for efficient lights.In the last year or so, the LED manufacturers turned the crank again, and the new LEDs, available in quantity one over the web, are unambiguously more efficient than fluorescent bulbs (technically speaking, white LEDs are also fluorescent). Our old undercabinet lights were halogen, hot, inefficient, and a pain to replace when they burned out.

The most efficent LEDs, unfortunately, look too blue, but when the selection at my favorite LED supply company included new “neutral white” CREE LEDs, I decided it was time to make the switch.

I bought 10, using one for a battery-powered helmet light, leaving nine to be run from a LED regulator. My steps to manufacture the mounted lights were:

  1. Solder leads onto star-mounted LEDs. Do this first, because it is easier to solder before it is mounted on the heatsink, and you won’t overheat the epoxy. Use lead-free solder, because you’re putting it into a kitchen, ok?
  2. Cut aluminum flat stock into pieces.
  3. Drill 2 holes per aluminum piece for screw mounts on diagonally opposing corners.
  4. Glue stand-offs onto back of aluminum pieces (on corners of other diagonal). The stand-offs ensure that the there is some air behind the aluminum plates for convection.
  5. Glue the LED to the aluminum plate, with epoxy or thermal epoxy, using two strong clamps on two sides of the “star” to squash the glue down as thing as possible.
  6. Screw the aluminum plates to the underside of the cabinet, taking care not to tighten the screws any tighter than snug — otherwise the plate will flex and pop the LED loose. If you do, either redo the epoxy, or just tack it back up with non-gel superglue (you want the thinnest possible layer of glue).
  7. Trim and solder the leads together, all in series.

This is sort of what it looks like under the cabinet. The red wire in the pair is connected to the series-connected LEDs (4 shown here), the black wire in the pair is the return. All the connections are soldered, the current is .35 A, the maximum voltage across the pair at any point is 28 V (limit of the power supply, and also of 9 3 volt LEDs in series). It is worth noting that these LEDs could run as much as .7A, but the light does not scale up proportionately, and the increased heat might require a less casual approach to heat-sinking.

IMG_0484.JPG

This is what it looks like, cloudy day, other lights off. It’s a completely adequate light, and the power meter says it’s pulling 11 watts (the power factor is 60, but compact fluorescents are no better — I checked).
IMG_0495.JPG
Asuming I did the heat sinks right and there’s enough air movement, those lights should be good for 50,000 hours of run-time.

And no, it’s not cheap — each LED cost $8.50, and the power supply was $31.50. However, undercabinet lights tend to be pricey, and are often inefficient, and even then they frequently look like crap. This is the killer app for LEDs — they have a great low profile, are not at too much of a price disadvantage, the low voltage/no glass/no mercury is a good thing in a kitchen. A true safety weenie would cover the exposed solder pads with a little epoxy or nail polish, and run the whole thing off a GFI protected circuit.

2 Responses to “More undercabinet lights”

  1. jk1joel Says:

    Nice project! Can you provide some information about the aluminum? How thick is it, and what size did you cut it down to? Is the aluminum something you can pick up at a local store or is it better to order it online?

    • dr2chase Says:

      It’s just aluminum flat stock, you can probably find it at any hardware store, certainly at Home Depot or Lowes. I think it’s 2 inches wide, cut to 4 inches long. Circulation behind the heat sink is a good thing, I might add a little (with, say, nylon standoffs).

      I would suggest, also ordering sample lights (warm white, cool white, neutral white) before doing this, to be sure that you like the color that you get, before investing in 9 of them. The off-color of the two non-chosen samples will be swamped by the other 7 LEDs, and you might like them mixed (cool+warm, e.g.) anyway. And also, using that linked driver, DO NOT attach an LED to an open circuit with the driver powered up; it may cook the LED. Connect the LED, THEN plug in the driver.


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