It's been almost a year since I started to "LEDify" my home, with results more or less encouraging, but only an accident made a??a??me find the best solution so far.
Step 1: Motivation
How often happened that you or someone in your family, by mistake, to overthrow the desk lamp? If you are like me, this has happened many times... For this reason, the last time my offspring slammed my desk lamp one more time, with an innocent "UUPS!", I exclaimed Enough!
Warning! CFL bulbs contains a small quantity of mercury and this is a very toxic substance.
If by accident or intentional, you have broken an CFL bulb, it is advised to ventilate the room as good as possible, in order to dissipate the toxic vapours.
I decided that I have to replace the CFL bulb from the desk lamp, with something more shock resistant...
But that could withstand the treatment of a 10 years child and at the same time to make enough light to work at desk in good condition, to be reliable in operation and decently priced? If only a few years ago, there was no a solution to this question, the answer is now clear: a power LED.
Step 2: Materials
As I already had some Cree MX6 Q5 LEDs with 3W power and maximum light output of 278 lumens used in some older projects, I decided to use them for this project too. The LED will be placed on a 5cm x 5cm heat sink recovered from the chipset of an old computer motherboard.
For simplicity, I decided to use a switching power supply of a mobile phone, perhaps together with an electronic adapter that would give me the necessary voltage and current to power the LED. For this purpose I have chosen the power supply of a defective mobile phone Siemens A52 having, according to the manufacturer, an output voltage of 5V and a current of 420mA.
An socket from am old CFL bulb should protect all the electronics.
Step 3: EVRIKA momentAccording to manufacturer specifications, Cree MX6 Q5 LED can be powered at maximum current of 1A at a voltage of 4.1V, and I expected I'll need a 1 ohm resistor to lower the voltage by about 1V from the 5V (given by the power supply) to the 4.1V accepted by the LED, and that only if the power supply would handle the maximum current of 1A.
In order to check the maximum current supported by the power supply I connected to his terminals various resistors, measuring in each case the voltage and then calculating the current. Here are the obtained values:
Load Voltage Current
-NA- 5.8V 0A
8.2 ohm 4.9V 0.6A
5.1 ohm 3.1V 0.6A
3.3 ohm 1.75V 0.53A
To my surprise, the power supply seemed to have by construction the current limited to about 0.6A, value he looks like it stand without problems. Testing in the same way other mobile phones switching power supplies, I found that absolutely all of them are limited by construction to a current from 20% to 50% higher than the one specified by the manufacturer, which now I find it makes perfect sense: any manufacturer will design the power supply so that it will not overheat even if the powered device would be damaged, even in short circuit ... and the easiest way to do this is by... current limiting!
I had therefore, a constant current generator limited to 0.6A, very effective (a power adapter cell phone heats up only slightly during operation), powered directly from 230V AC, ready-made by the factory, with very small size. And this is simply GREAT.
Step 4: Construction
For the beginning I made "the autopsy" of the power supply in order to extract the "organs" to be inserted in the body of the new bulb. As most power supplies are assembled by soldering, extracting consists of cutting with a saw blade... So pay attention to bruises for those less skilful...
In order to fit inside the body of the lamp, it was necessary to make some adjustments.
To fix the board inside the bulb, I used sanitary silicone, taking advantage of its resistance at high temperatures. Before closing the bulb, I attached to the cover (I used a screw) the heatsink on which is located the power LED.
Step 5: Results: Desk Lamp
And here's the bulb assembled. The power consumption is just under 2.5 W and the luminous flux is about 190 lumens, perfect for a economical, durable and resistant desk lamp. And all this for up to one hour of work, except of course the time for drying the silicone and heat-conductive adhesive used to fasten LED on the heatsink.
I was so excited about the success and ease of implementation of this project that after a few hours I had finished another LED bulb.
Step 6: Results: Hallway
Thrilled with the result, I continued to replace some of the CFL bulbs in my apartment with LED bulbs constructed in the same way. I will present these in "fast forward"...
For the entrance hall I used two Cree MX6 Q5 LEDs each having maximum power of 3W and maximum light output of 278 lumens, each powered by a power supply from old Samsung mobile phones. Although the current specified by the manufacturer is 0.7A for each power supply, after measurements I found that it is limited to the value of 0.75A.
Everything was assembled with velcro tape, adhesive and plastic spacers from PC motherboards.
Total consumption of the assembly is this time around 6W for a luminous flux of 460 lumens.
Step 7: Results: Bathroom
For bathroom I used an Cree XM-L T6 power LED, powered by using two switching power supplies from LG mobile phones. Each power supply unit can generate according to the manufacturer, a current of 0.9A, but I found the current practically limited to the value of 1A. The two power supplies are connected in parallel for a total current of 2A.
Under these conditions the LED will produce a luminous flux of about 700 lumens for a power consumption of 6W.
Step 8: Results: Kitchen
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If for the hallway and bathroom was not essential to ensure a certain minimum illumination, for the kitchen is a different story. I do not want that my wife or someone else to cut a finger while preparing meal and blame me for this, or worse, blame my precious LED bulb...
To make sure that this will not happen, I decided to use for my kitchen, not one, but two power LED Cree XM-L T6 each having maximum power of 9W and maximum luminous flux of 910 lumens, connected in series. For efficient cooling I used a heatsink recovered from a Pentium 3 Slot 1 CPU, which I attached the two LEDs using Arctic Alumina thermal adhesive.
Although Cree XM-L T6 LEDs can handle a maximum current of 3A, the manufacturer recommends for reliability a current of 2 A, for which they produce a luminous flux of about 700 lumens. After testing several power supplies that proved not to be current limited or limited to a current well above the necessary 2A, I managed to find a power supply which, according to the manufacturer, generates 12V at a current of 1.5A. After testing it using power resistors, I found the current limited to the value of 1.8A, quite close to the planned value of 2A. Perfect!
To secure the heat sink and the two LEDs I used two plastic spacers from a PC motherboard and two neodymium magnets recovered from a damaged DVD drive, all glued with superglue and also a velcro tape.
Although I expected this LED bulb to produce 1300 lumens, a light similar to the old 23W CFL bulb it replaces, I had the pleasant surprise to see that in reality the light produced is visible more intense, all for a power consumption of about 12W, almost half compared to the old bulb.
Step 9: ConclusionThe coolest part of this project is that you can use commonly available components, the only expense is for purchasing power LEDs.
In this way, you can get LED bulbs at a cost of half or even quarter compared to the price of an LED bulb purchased from a store.
I hope that in this way many power supplies from mobile phones will be useful again instead reaching the trash can.
This project is extracted from a series of articles published on a DIY web site I own http://www.schematics.ro/ where you are more than welcome.
Thanks for reading :)