Step 1: Motivation
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
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 Moment
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
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
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
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
Under these conditions the LED will produce a luminous flux of about 700 lumens for a power consumption of 6W.
Step 8: Results: Kitchen
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: Conclusion
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 :)