When I first built the shed the lighting was provided by work lights on cables hung from hooks in the ceiling. It wasn’t very good. As I mentioned in the shed blog I have installed 12V power supplies for the lighting. My next step was to design the lights themselves.
My first lights were 6W with adjustable brightness. I used a 555 timer to provide a variable pulse width ratio which I then used to switch 2 MOSFETs each set up in constant current circuit with a junction transistor. Each MOSFET powered 3 of 1W LED’s in series.
The circuit worked well pretty much straight from the design with little modification. I designed a PCB and ordered it from Itead. Their minimum order is 10 but that is what I wanted anyway. 4 weeks later they arrived. I assembled one and it worked straight away. The only problem was that I got a few artefacts when I put it on a long power cable. I had expected this and designed the PCB accordingly. The solution was a 100uF cap across the power wires.
They worked beautifully for several weeks. Then they started to fail. The LED’s, although not running hot and only at 80% of their power rating were going open circuit. Of the original 10 only 3 have survived fully working and a further 2 are part working. I’ve run out of LEDs and I can’t be bothered fixing any more.
In addition to the surviving lamps I now have some 10W strip LEDs. I have bolted these to large heatsinks. There are 2 with 4 LED strips on them over each of the workbenches and 1 with 2 strips in the stores. The 40W ones are really good for working under.
On 2 of the failed lamps I removed all the 1W LEDs and put 12V strips in. These come in 2 temperatures 3200K and 6200K. I used 2 of each on each lamp. All this went on a 0.5C/W heatsink of which I have several. I added a control for each temperature on a box on a 2metre cable. The result is a variable colour temperature lamp. I gave this to my brother who is an artist. He loves it!
The circuit itself works great. If only I’d chosen more reliable LEDs.
PS. I have now replaced several of the lamps with commercial mains voltage downlighters but the workshop still uses the old ones.
PPS. on the variable colour temperature lamp see seperate blog