Homebrew PCBs

At 03:47 AM 10/13/2006, Leon Heller wrote:
>I've just bought a ballast to go with a mercury lamp I bought on Ebay. I've
>just connected them up and the lamp is working OK. I rather stupidly put it
>on the bed with a dressing gown over it to keep the cat away, smelt burning
>a few minutes later and found the lamp had burnt the duvet cover and the
>dressing gown. 8-(
>
>Next step is to remove the outer envelope and do some test exposures. I'll
>rig up a suitable box to keep the UV away from me.

Couple of things: make sure that the phosphor is on the inside 
surface of the OUTER envelope.  That pretty much guarantees that the 
inside bulb is clear, and thus emits UV.

The reason I mention this is that I now see Mercury Vapor bulbs with 
a clear outer envelope.  Box usually mentions that the bulb is "UV 
safe" - this means that the inner bulb doesn't emit UV.

The other important thing is: that inner bulb needs to run hot.  The 
existing outer envelope provides thermal insulation so that the inner 
bulb can operate at the design temperature.

I wound up enclosing the inner bulb within a Hammond die-cast 
aluminum box about 4" x 4" x 7".  A large hole on the bottom allows 
the UV to escape, a mechanical shutter (motor driven) covers the hole 
until the timer switch is hit.

The enclosure allows the bulb to operate near its design temperature: 
its air-tight other than the single large hole facing downwards.  I 
find that the bulb takes 5 to 10 minutes to come up to operating 
temperature before I use it (don't really pay much attention to it: 
the electronic ballast I use sort of squeals until the bulb reaches 
operating temperature).

The whole thing works well - I'm on my 2nd bulb now.

dwayne

-- 
Dwayne Reid   <dwayner@...>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

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