Introduction: The Return of the Dead Flatbed Scanner
How a dead scanner can return as a printed circuit board UV lamp. Keep that cover closed !
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Step 1: Forewords
I made this Ultra Violet bed to make printed circuit boards a few years ago without Instructables.com in mind, so rather than a step by step pictorial description of how I made it, I'll provide you with a few pictures of the finished work and hints on how you can do the same. Hope this will help anyways.
First of all, safety. Notice that this is a mains powered device so maximum care must be taken in the design to insure that for no reason someone may come into contact with live parts. If you are not sure about medium voltage (mains) electrical wiring practice ask a friend or someone else whom is.
Step 2: Inside the Case
Just a reminder first: 100/220 ac mains can be very dangerous! Oh, I think I already told so.
First thing I did was to disembowel the scanner, after all what I needed was the case with glass and cover. No electrical parts where reused. Of course you may want to save the motors, belts, screws, head parts...You know, almost everything.
Then I opted for 3 tubes (around 8 Euro each), with ballasts and starters (6/7 Euro for each set). The switch, fuse holder and mains socket I scavenged from somewhere.
For the bottom plane I used a tin sheet. This acts as a sort of mirror/diffuser for UVs.
I used also some scrap aluminum bars from kitchen furnitures, their colour in the pictures tell it. Spacers and screws as required.
Now, the pictures show the electric diagram and the interior of the UV bed.
The circuit is based on three TL5 8W wood light tubes. Each tube is powered by its own ballast and starter . The number of tubes can be increased at will. The circuit is provided with a safety fuse and a power switch. A power socket (taken from a PC power supply) complements the circuit.
All metallic parts inside that have an external metallic counterpart electrically connect to it, must be earthed i.e. connected to the ground line. This is an important safety measure: if something goes wrong and the metal inside becomes 'live' the safety switch or fuse you have in your home trips off and no one is injured. Otherwise the external metallic part may become live without anyone noticing until touched. In my case, since I used a metallic bottom and metallic spacers and screws to hold it to the case, I bolted the metallic bottom to the ground.
As I am writing I think that I should have bolted to ground the back panel which is metallic and can be reached externally as well. I'll do so.
Step 3: A Few More Details
A few details now.
Grommets must be used where the wires cross the metallic plane so as the plastic insulator of the
electric wire does not wear out against the metal plane.
The fuse must be rated for the lamps used. In my case 3x8W 220Vac require a 0.5A fuse.
The tubes, ballasts and starters must be rated togheter. Too high rated the ballast and the tubes
get burnt, too low rated and the ballasts burn. Ballasts are typically rated with ranges e.g. 4-20W.
With different wiring and rating one ballast can serve two tubes. Check with the ballast supplier.
As a second thought, I think I shouldn't have removed the scanner's head. I should have mounted one single tube to the moving head of the scanner and use the stepper motor and belt to move the head back and forth.
To provide a uniform lighting the head should have been moved with a non-uniform speed (arcsinusoidal, or inverse sin function, I am guessing). Exposure time would be given by the head-lamp scanning faster or slower as required. But that's another story
One final important notice: UVs are dangerous to the eyes, so do not stare at the tubes when lit.