[beery]

Hi all,
When I started my current job 4 1/2 years ago I purchased a LightCraft LC8076 bench magnifier lamp from RS to use on my work bench. I liked it so much that I bought one for use at home, this time from Rapid Electronics.
The lamp at work was on almost every day and it was not long before the tube wore out. What actually seemed to happen is that the electrolytics on the electronic ballast failed causing the tube heaters to remain on until they burnt out, which also discoloured the white plastic of the lamp. I re-capped the ballast, though neither RS or Farnell had 105 degree caps with the same small dimensions as the originals (that may be why they were rubbish). I then got a replacement tube from Farnell (RS didn't stock it) and it has been fine so far.

Now to the lamp at home. Well I should have got round to changing the caps on the ballast before they failed, but I didn't. The result of course is that it failed in the same way as the one at work, with the same discolouring of the plastic moulding. However, this time round I found that the tubes are no longer manufactured. Lightcraft now sells the entire bench lamp as an LED version which is much more expensive than the fluorescent version was. What they don't sell of course is an LED conversion kit, so I had to make one...

I drew up a ring shaped PCB using Altium. It has 8 parallel groups of 7 series connected LEDs. Each lot of 7 LEDs has a 150 ohm current limiting resistor and the whole thing runs at 24V DC 160mA. I made the initial prototype by printing out the component layout (top silk screen) on to an adhesive label and sticking it on to some stiff card. Using a compass point I created the holes for the 56 LEDs. I pushed the component legs through the cardboard, bent them flat and soldered them up. I used 2 rings of tinned copper wire for the power tracks. To power the LEDs I cut off the 2 pin Euro mains plug and connected an external 24V PSU. It all worked well, so far so good, but I was not finished yet...

Cheers
Andy