LED Appliance Bulb Replacement

If your microwave or other appliance has a built in light, chances are you have been wondering how to replace the anemic, inefficient bulb in it with a high power LED.  Your time is at hand, as in this Instructable I will show you how to replace a 40W incandescent appliance bulb with a 3W white LED that will generate as much or more light at a >10X reduction in power consumption.  Total project cost around $10.   Fun, easy, cheap.

The first step is to separate the glass bulb from the metal socket/ferrule/base or whatever the heck you want to call it.  You can do this by breaking the glass and prying out any remaining scraps stuck in the base or you can use a heat gun to try and get the glue holding the glass in to soften.  In either case, be careful and try not to cut yourself .

Once you get the glass out you will need to remove the wires for the filament from the base and use a soldering iron to attach your own wires.  The "button" or nib at the base of the metal bulb base is made of solder that you will need to heat up and get your wire attached to.  Not too hard once you get a look at it you should have no trouble.   Attach the "live" (red) lead to the button/nib and the "neutral" (black) wire to the base body.  Use black for live and white for neutral if you are looking to match typical in home wiring.

With the wires in place and solidly soldered, take your wood scrap and trim it to size.  With the power off to the fixture you are trying to put the LED into, you will want to screw the metal base with wires into the fixture to see where the base ends up rotationally so you can align the LED with it.  Unlike the incandescent bulb, the LED will be directional and you need the LED to point the right direction.  Take a marker or other method to mark the alignment for the wood scrap.  Remove the metal bulb base from the fixture and glue the wood strip in place according to your mark with epoxy (if you use hot glue it can soften and fall apart in use, which is very dangerous since this is connected to 120VAC).  Reseat the assembly in the fixture to ensure your alignment is good enough.  A few degrees off is no big deal here.

The next step is to use epoxy (if you use hot glue as I originally did, the glue will soften as the bulb heats up and fall apart, which is very dangerous with it being connected to 120VAC) to attach the aluminum channel to the wooden base to serve as a heatsink.  Be sure to keep the aluminum from touching the metal bulb base so that the heatsink is not electrically connected to the metal base which will be connected to the AC power.

UPDATE:  After having the bulb powered for a few hours with the broiler going at 550F the hot glue holding the heatsink to the wood base softened and let the assembly droop.  So I would recommend that an epoxy or other glue be used to bond the heatsink to the wood base.  The combo of a really hot environment due to the oven heat rising and the heat created by the LED is too much for hot glue in this application. 

The next step is to wire the driver circuit up and attach it to the wooden support.  First remove the wires that come with the driver and use solderwick or similar to clear the holes of solder.  Thread your wires attached to the bulb ferrule into the holes on the driver board and solder the wires to the board.  Repeat this for the wires that will go to the LED and use your own wires that will be long enough to reach the front of the heatsink.

With the driver connected to the AC wires, glue it in place with epoxy.  You can wait to glue everything in place until you have tested the system but be extra careful with handling the wiring/circuit/etc to prevent shorting when powered. 

To attach the LED, solder the DC drive wires to the appropriate pads on the LED which should be labeled.  Using an appropriate epoxy such as thermally conductive epoxy ,  electrically conductive epoxy or JB Weld.  The back of the LED board is not electrically connected to the LED and if you were careful with the driver the heatsink should be isolated as well so using a conductive adhesive is OK.  While the epoxy is curing, clamp the LED down to minimize the distance between the LED and the heatsink.

Now that the whole thing is done, screw it into your light fixture.  When screwing the bulb into the fixture, your care in measuring the final position taken in Step 2 will determine if your LED points down as desired.  You can tweak the bulb a bit in the fixture if needed but if you are off by a bunch you might have to add solder or remove solder from the nib/button at the end of the bulb to change the rotational position of the bulb when seated.

If when you turn on the power you see sparks and release the magic smoke, then it is back to the drawing board.  If all the lights in your house go out, you might want to find the breaker panel.  If you are transported to the 8th dimension, look out for the Red Lectroids.

Pictured is a microwave where the left bulb is a traditional 40W incandescent and the right is the pictured LED bulb with 3W nominal consumption.  The light outputs are similar, with the LED light being somewhat cooler in color than the incandescent.  Measurements using a light meter show that the incandescent is outputting about 250 Lux at the cooktop surface max and the LED is outputting about 300 Lux at the cooktop max.  For a >10x reduction in power consumption we've gotten the same or more light output.  Not too shabby.  Take that Mr. Edison.

So there you have it, a simple LED project to save power and reduce maintenance and no one will be the wiser.  That is unless you look forward to replacing your bulbs, because  then you might be disappointed as the LED will likely last longer than your appliance.  If you use hot glue, not so much.