Introduction: High Power LED Wake Up Light (+/- 15Watt)
*2020 edit note:
First of all I don't use the fan anymore and that seems to be ok. It gets hot, but nothing has burned down yet.
With some new insights and since these leds are so dirt cheap, I would use more than just 2 and add some 3W single LEDs. The benefit of this is that the 10W LEDs need about 9V, but the power supply provides at least 12V. Using for example a 10W LED in series with a 3W LED would probably reduce it's current draw. A dedicated current regulating circuit would probably be better but I found this to work for at least 12V power supplies. Using 4 LEDs in series (or a single 10W + a 3W which is sortof the same, the 10W is 3 leds in series, and that 3x in parallel) results in a current draw of about 0.2A. The extra voltage dropped by the MOSFET will reduce that even more, so you could tune it this way to be in line with whatever the rating is of your 12V power supply. This would also make the high power 2 ohm resistor unneeded.
Another alternative is to use LED strips. You can ditch the 2 ohm resistor, and use a smaller heatsink for just the MOSFET.
This instructables is an extention of the Sunrise Alarm Clock https://www.instructables.com/id/Sunrise-Alarm-Clock-1/ by https://www.instructables.com/member/DIY+Hacks+and+How+Tos/. Credits for the original idea and circuit go to that member. I merely adapted it to my needs and materials at hand. The instructable in the link features a wake up light with small 5mm LEDs, this instructable is about high powered LEDs with a total theoretical power of 20W, which exceeds the output of a 60W incandescent bulb. I went for the higher output since it is not super expensive, waking up with bright light is healthy, and I'm notoriously good at not waking up. Therefore I will still use my cellphone as backup alarm. I can also leave the light on for some time after getting up and use it as a regular light. Especially in winter times when it can be still dark outside when getting up some bright morning light can be good for your daily rhythm.
Step 1: Materials
As always, you need some materials. I always try to use components of old circuit boards since they dont cost anything, and next to that recycling is environmental friendly. When I need to buy stuff I generally use ebay, since some Chinese sellers offer free shipping on already cheap components. Drawback is the shipping time ;)
Used for just the wake up light itself:
- Wall Socket Timer Switch (I prefer a digital one since the non-digital one I had was making an annoying rattling noise)
- AC-DC Adapter (This one is salvaged from a modem which wasn't working properly, the provider replaced it but forgot to take back the adapter. Secondary output specifications stated are 12V 2A DC.)
- IRF510 MOSFET (ebay, 1 dollar)
- 4.7 MOhm resistor (~1W or 2W I think, but the normal small ones will do. Value is not critical, must be large)
- 100 kOhm Potentiometer/variable resistor (For fine tuning. Value is not critical but must be say 10k+)
- 2200 µF 16V Capacitor (Or something similar, as long as you don't have a rating lower then the voltage you put on it)
- 10W 9-12V 0.9A Warm White COB LED (ebay, 1,31 dollar)
- 10W 9-12V 0.9A White COB LED (ebay, 1.40 dollar)
- 2 Ohm 10W resistor (ebay, about 3 dollars for a 5 pack)
- CPU heatsink with 12V fan (salvaged from an old computer, maybe fanless will do, depending on your heatsink)
- Circuit Board
- Thermal glue
- Insulating shrink tube or tape
- Some tools such as a soldering iron, pliers, etc.
Optional for fan:
- Set of resistors for running the fan at lowest possible speed, PWM is also an option but I went for the easy way out. If I recal correctly I used a 1 or 2W resistor 150Ohm in parallel with a 0.25W 560Ohm resistor. I just picked the maximal amount of Ohms at which the fan would only just run.
Note on values for the capacitor, Mohm resistor and potentiometer: These don't need to be exactly like this, different values will do just fine (just test if it will do or not). This setup reaches full power in about 30 to 45 minutes, so lower values for the Mohm resistor and/or capacitor might be better.
Step 2: The Circuit
Some part of the circuit can probably be done differently, perhaps better. This is what I could do with my knowledge of electronics.
How does it work?
The 2Ohm 10W resistor slightly lowers the voltage/current. Next, the capacitor is slowly charged through the 4.7 Mohm resistor. The voltage across this capacitor is rising over time and is the input to the IRF510 mosfet. This current goes via the mosfet to the ground, and slowly opening up the possibility for current flowing from the LED's through the mosfet to the ground, thus slowly lighting up. There also is a switch so the fan can be turned on or off. See image comment for which mosfet connection is which.
Step 3: Testing
First of all: WARNING!!!!!!! THESE LEDS ARE VERY BRIGHT. I LOOKED STRAIGHT INTO THEM WHICH I DON'T THINK IS A GOOD IDEA.
The circuit was first tested with a lot of different setups on a breadboard, until this one was found which I was happy with. Test your circuit and make sure the components don't heat up to much. Don't test for just a few minutes, let it run for an hour or so. If some things get hot, make sure they are close to the heatsink and attached to it with the thermal glue. With my setup the 150 Ohm (~2W?) in series with the fan got quite hot, so when I was testing I placed a piece of scrap copper against it to remove excess heat. Worked quite ok. Conclusion is, this resistor needs to be a bigger one (as in actual size/Watts it can handle) or be attached to the heatsink. The 2Ohm 10W also heats up a lot, though it should be able to handle this. Nonetheless I glued it to the heatsink. The mosfet also heats up quite a bit, this one should also be attached to the heatsink!
I somehow partially destroyed my warm white LED, probably when melting the shrinktube around it's terminals. The LEDs consist of 3 strings of 3 LEDs in series, and one of the strings died. So basically I now have 5 strings of 3 LEDs, of which 2 are warm white and 3 are cool white. Therefore maximum amperage goes down a bit, its now 0.9+0.6=1.5A. I could replace it, but I don't feel like doing so.
Step 4: Assembling
Ok so please look at the pictures and comments for what I've done. One remark on troubleshooting, I had a working circuit on the breadboard. Then I made the PCB and had some flickering issues which I couldn't explain. Took apart my first build, swapped some components for fresh ones but still the same problem. Turns out the problem probably was flux still being on the circuit and connecting some leads of the MOSFET. Solution was simply washing the pcb with water and some soap. PLEASE don't make this mistake, you don't want to have the same frustration I had.
A note on the aluminium sheet, it would probably be easier to just buy a better kind of glue, such as arctic silver thermal adhesive. This was cheaper for me though, so I did it this way.
Step 5: Using the Wake Up Light
Since these LEDs are so bright I found it best to place the wake up light on a closet or something else which is high, with the LEDs facing the ceiling. This way you have a nice and bright diffuse light with no possibility to look directly at the LEDs. For best results pick a closet close to your bed. As a wake up light I use it without the fan, therefore I will not turn it on for longer than an hour without the fan (test this, every build is different!).
Since the fan is used at minimal speed for noise reduction it might get a little hot if it is used for a long time. Be sure to check this if you plan to turn it on for more then a few hours. My setup remains cool to the touch when the fan is on, so it's fine.
See the above picture for it in use. The light colour and intensity you see on the picture is not exactly what it is in reality due to the camera adjusting stuff. Should be a bit warmer colour, brightness is enough to light up the room (2.5 x 3 meter ish)
Participated in the
Green Electronics Challenge