Shed Lighting

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

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