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.

Step 1 Assemble your components

This project will require a handful of parts, pictured below.  Your project may vary slightly depending on the bulb you are replacing, but the basic idea will be the same.  The main components are the LED and the driver. 

The driver is a cheap 120VAC to constant current unit built and sold direct from China.  This is not a particularly safe, elegant, or reliable driver but the price is hard to beat.  When working with electricity, especially 120VAC, be careful and do not take any chances.

The LED is a Cree XRE high efficiency warm white source, rated at 74 Lumens at 350mA.

List of Parts
Cree XRE Warm White LED   http://ledsupply.com/creexre-ww.php
(You should get the XPG now, since it is more efficient and cheaper  http://www.ledsupply.com/creexpg-ww105.php )
3W 120VAC LED Driver  http://www.dealextreme.com/details.dx/sku.13552
Bulb to be replaced
Scrap of thin wood (plywood or popsicle stick)
Small section of aluminum channel for heatsink
Misc Wire
Misc epoxy (i.e. JB Weld)

Comments

[supercell2000]

What gauge wire did you use for this?

[jmengel]

The driver modulates the output voltage to reach the programmed output current. The driver I specified for this build is a 1x3W driver pushing 650mA constant current designed to drive a single LED. The circuit consists of a step-down transformer a rectifier, and then a buck type constant current regulator. Using this circuit to run a 3-up style LED star is possible since the constant current driver doesn't care how many LEDs are in series as long as the supply voltage is higher than the forward voltage of the series LEDs (~10V for 3-up) plus some overhead (~1.5V) as well as the total power dissipated in the driver is less than rated maximum. Typical driver ICs can handle 9 LEDs in series before they max out. However, the other parts in the chain may not be rated for running 3 LEDs at 3W each. Particularly the transformer and rectifier may fail. In any case, the driver will run hot at 3x3W and wrapping in electrical tape may not be a good fix as the tape softens and unwraps when really hot. I've run 3x3W for short periods with these drivers but have not tried long term running in an enclosed space. If the door switch were to fail, I'd be worried about the driver failing after being on for a long time. The method of failure may or may not damage the fridge or cause an electrical fire. Caution is warranted. That said, the pictured heat sink is probably inadequate to run a 3-up for long runtime without degrading the LED lifetime (15,000 vs 50,000 hour lifetime). The two LEDs shown are probably running pretty damn hot if the light is on for more than a few minutes.

[mvipond]

What is "pretty damn hot"?

I am currently connected to a thermo couple on the counter (room temp, not fridge) at 155 deg F. After 25 minutes.

[jmengel]

Where is the thermocouple? The maximum junction temp is 150C (300F) for an XPG according to the datasheet. With a 6C/W junction to thermal pad resistance, and a 3C/W solder/star/paste to heat sink resistance, and a 6C/W heat sink resistance to the environment the temp at the junction could be already at 133C. (70C at thermocouple on heatsink + 6C/W * 6W (2 LEDs at 3W each) + 3C/W * 3W + 6C/W * 3W)

Running long term at a junction temp of 130C will reduce the LED lifetime. How much, I don't know. 30%? In a fridge application I would say the LED will still outlive the fridge unless the door switch fails and the LED starts running around the clock.

As a rule of thumb (ha!) I'd say you should be able to touch the LED heatsink indefinitely without burning yourself for a good thermal design for long runtime. In an intermittent application like a fridge, you are probably fine.

-Jon

[mvipond]

Thermocouple was right between the two LEDs, on the heatsink, so, yeah, probably too hot for long term use, but that is at room temp ambient too.

I am gonna order some more supplies, and try again, with an improved heatsink design.

In the meantime, I feel comfortable using these in the fridge. Awesome instruct able! Thanks for all the good advice.

[mvipond]

bump (I know this is a year old but...)

I just built two of these, I took some liberties with the design, and actually doubled the LEDs per "replacement bulb" Still trying to understand all the LED terminology, and was hoping to build a couple more "bulbs" with the cool white emitters. here:

http://www.ledsupply.com/creexpg-w139.php

and am concerned that the original drivers would be appropriate for this different LED.

These are for my refrigerator and freezer, each replaces a 60 watt incandescent cool white bulb.  I just couldn't stand having 120 watts of heater in my fridge, even if it's only on (in theory) when the door is open.

Input would be appreciated.  I was also curious if there was a different driver I could/should use to drive two LEDs, as in my current design, I just used two drivers.  The form factor of this was nice, but it's kind of "cheesy".

Thanks!

[jmengel]

The drivers will work fine, they provide a constant current which is what any LED prefers. The level of current desired may vary, but the XPG LED will happily run on these drivers. You can even use one driver and put the LEDs in series, wiring the + from the first of the LEDs to the - on the other and then having the + and - leads from the driver connect to the - on the first LED and the + on the second.

Having this in your fridge is a little bit concerning since you reach into the fridge with your bare hands and may contact the 120VAC wires. Make sure all the "hot" wires are covered and that the heat sink is isolated from 120VAC. Also be sure and use whatever bulb cover came with the fridge. I know some older fridges don't have a bulb cover, so if that is your case then I would be extremely careful. Additionally, the bulbs are certainly off when the door shuts. If not, all your food would spoil as your fridge ran flat out to try and keep cool. If you are worried about the theory of it, pull the shelves and the food out and climb inside and shut the door to find out. Good luck!

-Jon

[mvipond]

Thank you for the quick reply! Regarding running the LEDs in series with one driver, how would that affect the light output?

Could a person use one of the "3 up" led stars with just one of these drivers?
http://www.ledsupply.com/creexpg-w354.php

The fridge is a bit of a mess actually. It's an LG french door model, one of the first ones (the new ones have LEDs from the factory) and there are well documented problems with the door switches failing, and the bulbs staying on. This results in the bulb housing actually melting, pictures have been seen on the internet of a stringy mess of melted plastic on top of food. LG has no real response except "changing the bulbs voids the warranty" SO that's the "why" for me with this project.

Details - I didn't like the "take the glass off of the lightbulb" although, if you had a non-standard lightbulb, that would be your best bet. Anyway, the base I used is actually one of those nifty things that you screw into a light socket, and make a "wall outlet" out of. SO, I just whittled out the plastic a bit, to expose the contacts, and soldered in the 110v leads. Then I filled that whole area with clear (non-electrically conductive) epoxy effictively insulating the 110v from the rest of the assembly. I ran the 110v leads up to my drivers, and then just wrapped the drivers with electrical tape. Further protection from the fridge user contacting 110V is afforded by the fact that there is in fact a clear plastic shroud over the "bulbs"

The installed look is awesome.

I don't understand completely the lumens that this is putting out, as the charts are a bit confusing (how many mA?) but I would say that these things are almost comparable to my O.E.M. 60 watt bulbs in this application.

[fixrupr]

I just received the driver but it doesn't have the 4 white wires it has 2 white and 1 red and 1 black. I examined the circuit board and it has a positive for the red and black for the negative. The 2 white wires don't have anything on them. Should I connect those to the bulb and not the led?

[jmengel]

My guess is that the red and black are the + and - for the LED and the white are the 120VAC lines which will need to be soldered to the bulb ferule for interface with the 120VAC supply mains. The polarity of the 120VAC lines in not critical for this application.

[fixrupr]

Thank You I also thought that but wanted to be sure. I will post a picture when it is complete.

[fixrupr]

My bulb is complete. I purchased the heat sink from Radio Shack for $1.19 used a popsicle stick and JB weld. The JB Weld was a mess. I had to constantly clean up and I had to use a clamp to make sure it stayed in place. I had to wait 4 hours for it cure hard enough for it work. I used it on the stick, wait 4, then on the driver, wait 4 then the led wait another 4 hours. It works I can't believe it. I thought I was going to short out the microwave. I thank everyone for their advice. Before this I was buying bulbs all the time.

[fixrupr]

Bulb has been on since June 5th 24 hours a day and has not gone out. Awesome!!!!!!!!

[jmengel]

Glad to hear it. Mine is still going strong too, although not 24/7.

-Jon

[Karlboer]

Bulb is complete. The dimmed setting makes no difference to this bulb (which is fine by me. My question below was just to make sure it wouldn't hurt the bulb). It cost me about $30 for supplies for two bulbs. I think it will easily save me $15/year in electric & cost of bulbs. Awesome! Thanks!

I gotta say that the light is a little..... harsh. Not quite as yellow (warm) as the incandescent). I was also surprised that the bulb takes a half second to turn on once the button is pressed. I wonder why.

[Karlboer]

A few days after posting this, by bulb burned out. The driver died. I had it hot glued to the back of the heat sink, and the heat sink melted the glue, causing a short circuit (I think that's what happened from my best guess). I still need to take the time to replace the driver and increase the size of the heat sink. Make sure your heat sink is big enough to dissipate the heat generated. I believe the LED came with a sheet that said the heat sink needs to be at least 3 inches (I assume that is total surface area, though it didn't say).

Let's try this again!

[jmengel]

I edited the text to caution against hot glue in any location on the project. Sometimes it is so nice to be able to put a project together in minutes with hot glue, but like fat free Olestra potato chips there is no free lunch.

[jmengel]

Yes, I had a similar problem with hot glue although the bulb did not self destruct. I switched to an epoxy (JB Weld). If you dial back the current it will also help on the heat. The big issue for me was that the bulb sits inside a metal can on the bottom of my microwave, with a glass front, so that heat is pretty much trapped with no airflow. Add to that the fact that the bulb is usually on when I am using the stove, and heat is a problem. I expect that the LED life will be shortened from 50k hours, but since I don't use the bulb more than an hour a day I think it will last longer than the stove.

If it is just the driver, you should be able to drop in another one ($2). I usually order them in packs of 10 since they are cheaper that way and nice to have around if they burn out.

Thanks for sharing your experience. As convenient as hot glue is, it isn't for every project.

[Karlboer]

I ordered and installed the new driver on a larger heat sink. This time I wire tied (plastic) the driver to the board. Somehow I just couldn't bring myself to use epoxy to mount the driver. I finished the new light in May, and it has been going strong ever since.

Just to clarify, I am using it under the microwave in the same situation you did. There is no place for the heat to escape in that little glass and aluminum coffin.

Thanks again. It has been a fun project, and the results are fantastic!

[jmengel]

The lower wattage incandescent bulbs are pretty yellow (2500K), even the "warm" white LEDs are only rated ~3000K and that is usually seems pretty generous.

LEDSupply.com is also now selling warm white Cree XP-G single LED star boards that are about 40% more efficient than the XR-E LED that I used. 105 Lumens at 350mA as compared to 74.

http://ledsupply.com/creexpg-ww105.php

I've noticed the start up lag as well. I attribute it to the time to charge the smoothing cap and the time needed for the current control loop to ramp up and stabilize.

Glad to see your successful bulb build. Let me know how it holds up. I've had no problems with mine, although it doesn't get used a whole lot.

-Jon

[-max-]

start using the XM-L T6 LED!!! it is 100 lumens per watt, and 130 lumen per watt @ 700mA

[jmengel]

My reading of the datasheet puts the T6 bin at 140 lumens/watt at 700mA which is better than the XP-G R5 140/watt at 350mA and 115 lumens/watt at 700mA in cool white. I prefer a warmer white with a better CRI, at which point the XM-L and XP-G's are more similar in performance. Additionally, using more XP-G's and lower wattage is easier to heat sink and easier on the eyes. I'm currently building some 5 foot linear 15x arrays for a closet which will run each LED at 300mA for a distributed and easy on the eye >1000 lumens. Try looking at a single 1000 lumen XM-L at 3000mA? Painful.

The price for XM-L's is also still pretty high as they are "cutting edge", almost 2x the XP-G. Do you know of a good source for XM-L's at a decent low quantity price?

Thanks for the tips.

-Jon

[Karlboer]

I'm also wondering if this will work on the dimmed setting, Anyone know?

[jmengel]

Let me add, that the triac dimmer may not damage the driver that I used but it will most likely increase the flicker visible in the light while reducing the output. It would be like really low frequency PWM (pulse width modulation). Since the LED turns on and off so fast, the low frequency pulsing would probably be visible. Especially out of the corner of your eye where fast rod receptors are more prevalent. The impact on the smoothing capacitor on the driver for the LED is not clear, you may find that below a certain "dimming" the LED driver fails to fire at all and that the flicker is so bad that you leave it undimmed. Try it and let us know how it goes.

[jmengel]

The driver I used will not work on a dimmer. You may be able to find an LED driver that works with an incandescent dimmer but these are more specialized, complicated, and expensive. A typical line voltage dimmer uses a triac to chop the AC waveform, which effectively reduces the on-time of the light bulb. This works fine for halogen and incandescent bulbs which rely on a hot filament to generate light but is damaging for most florescent and LED bulbs.

[Karlboer]

I'm starting with a GE bulb base. The casing seems to be aluminum - or at least not solderable. I'm trying to figure how to attach the neutral wire without solder. If I can't figure it out, I may need to buy a Philips bulb to start with (that's the one that appears in the first photo anyway).

[jmengel]

Solder would be your best bet, but you could probably use a conductive epoxy since the current would be low.

[zack247]

very nice! i have these ikea under-cabinet lights that use some wierd bulbs that i can hardly find anywhere and cost quite a bit, they are always burning out and this might fix it, but the lights plug into a white box thing that the ac power goes into, is this an inverter or something?

[jmengel]

Probably not an inverter, maybe a step down transformer to low voltage AC. Look on the IKEA website and the product description should give you specs on the bulbs. Another way to tell would be to measure the voltage across a bulb when it is on or remove the bulb and measure the voltage. It is probably either 120VAC or 12VAC in the USA. Be careful when working with AC power, if you don't know what you are doing get someone who does.

[zack247]

so if it is a 12v or 120v one this LED replacement would still work, right?
i'll see about testing it, i can hook a 9.6v rechargable battery up to it and the light turns on at almost the same brightness as if it was hooked up to the box, does this mean it probable produces 12vDC?

[jmengel]

If the light is bright at 9.6VDC then the box is a step down transformer that outputs 12VAC. It might be 12VDC, but for lighting it doesn't matter much (except for 120Hz flicker) so usually it is 12VAC since it is easier and cheaper.

The LED replacement I detailed in the Instructable will not work as shown in your application. You will need a different drive circuit. See the link below for a suitable driver circuit:

http://www.dealextreme.com/details.dx/sku.13557

[zack247]

wouldn't the led just run off of 12v?

[jmengel]

No. LED's require a constant current rather than a constant voltage for proper operation. Certainly you could come up with a resistor that when placed in series with your LED would keep it from exploding when the 12V was applied. However, the efficiency would suffer. If you were to run 350mA at 12V with a typical Luxeon Rebel 3-up star, the Vf (forward voltage) of the 3 LEDs in series would be about 10V. As a result you would need a resistor to drop the additional 2V at 350mA, which would be about 5.7Ohms and 700mW. Since the LEDs would be dissipating about 3.5W, you'd be wasting 20% of your power right off the top (0.7W / 3.5W) as heat in the resistor. Most constant current drivers are at least 90% efficient, which means you'd be wasting 10% as heat in the driver. Not to mention the increase in resistance of the resistor and Vf of the LED with heat which would reduce the drive current as the bulb heated up leading to reduced output.

Long story short, you could run the LED right off the 12V but you'd need a power resistor, and the brightness and efficiency would be worse when compared to a constant current driver.

[Scott_Tx]

Pretty neat. I'd never noticed those 120 led drivers on dealextreme before.

[jmengel]

They are handy, and effective, but pretty primitive. Basically a tiny step down transformer, a diode bridge and a filter cap. You can get a quantity discount as well which makes replacing a bunch of bulbs easier. They recently added higher power versions as well, with up to 30W for around $11.