Re: gEDA-user: [OT] Fluorescent tube help

[David Smith <Dave.Smith@xxxxxx>]

Chris Smith wrote:
> I recently purchased an old, second-hand UV exposure box to try making
> PCBs at home.  One of the tubes has started to fail and in replacing
> them I have noticed something odd: the box takes two 12" 8W T5 tubes,
> but has only a single 13W switch-start ballast.  I assumed that a
> previous owner uprated the tubes without changing the ballast, but in
> looking for a replacement I have become stuck.
> 
> 2. two tubes can be wired in series here in the UK because of the higher
> mains voltage, but the suggestion is that a special ballast might be
> needed.  Again, no explanation why.

From my limited knowledge of how fluorescent tubes work...

During the start phase, the starter short-circuits the tube allowing
current to flow through the starter and the heating filaments at the
ends of the tube.  If you put two tubes in series and the starter is
integrated into the ballast, how do you wire them so that this mechanism
still works?  The starter won't be able to heat one end of each tube.



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