Running two fluorescent tubes from one ballast - NOT! (in UK)

[Rick]

Hi all,

I've just built a UV exposure box using 12 inch tubes, tying two tubes
to each ballast. The ballast (RS part 562-110) is rated for this
according to its spec sheet and I've wired them up correctly with the
tubes in series and a normal switch starter across each tube. The spec
sheet showed the wiring diagram below:

Note: Mains at 240V or whatever it is today in the UK.
=======
L o--------^^^^^^^-------+ +-----+
Ballast | | |
(Inductor) +|-|+ |
| - | |
| | +-+
Tube 1 | | |S| Glow Starter
| | +-+
| - | |
+|-|+ |
| | |
| +-----+
|
| +-----+
| | |
+|-|+ |
| - | |
| | +-+
Tube 2 | | |S| Glow Starter
| | +-+
| - | |
+|-|+ |
| | |
N o----------------------+ +-----+

It does not work! The tubes do not even flicker. If I short across one
tube, the other will start and when I remove the short, the shorted
tube starts.

Is it just that the ballast spec sheet is wrong about being able to
support this?

I have put a capacitor (X2, 0.68uF) across one of the tubes in place
of its starter and the tubes fire up OK like this. Is this:
a) safe?
b) likely to reduce tube or ballast life?

Thanks,
Rick.

 

[Dimitrij Klingbeil]

Hi all,

I've just built a UV exposure box using 12 inch tubes, tying two tubes
to each ballast. The ballast (RS part 562-110) is rated for this
according to its spec sheet and I've wired them up correctly with the
tubes in series and a normal switch starter across each tube. The spec
sheet showed the wiring diagram below:

Note: Mains at 240V or whatever it is today in the UK.
=======
L o--------^^^^^^^-------+ +-----+
Ballast | | |
(Inductor) +|-|+ |
| - | |
| | +-+
Tube 1 | | |S| Glow Starter
| | +-+
| - | |
+|-|+ |
| | |
| +-----+
|
| +-----+
| | |
+|-|+ |
| - | |
| | +-+
Tube 2 | | |S| Glow Starter
| | +-+
| - | |
+|-|+ |
| | |
N o----------------------+ +-----+

It does not work! The tubes do not even flicker. If I short across one
tube, the other will start and when I remove the short, the shorted
tube starts.

Is it just that the ballast spec sheet is wrong about being able to
support this?

I have put a capacitor (X2, 0.68uF) across one of the tubes in place
of its starter and the tubes fire up OK like this. Is this:
a) safe?
b) likely to reduce tube or ballast life?

Thanks,
Rick.

Your approach is generally safe, but it could lower the lifespan of the tube
with the cap.

The problem seems to consist of wrong starters. You will need some that can
act reliably at 110V, not the ones for 220/240V. The starters often have a
small cap inside (some nF only), so the 2 caps form a 1/1 voltage divider
and each starter gets half the mains voltage when the circuit is switched
on. The starters must be able to handle this voltage, else the tubes won't
power on.

The correct solution would be 2 new starters, but you may want to try one of
the following 2 options. None of them is really optimal, but they may be an
alternative.

1.) See Schematic (safe, but could take longer to start):

=======
L o--------^^^^^^^-------+ +-----+
Ballast | | |
(Inductor) +|-|+ |
| - | |
| | +-+ Only One
Tube 1 | | |S| Glow Starter
| | +-+
| - | |
+|-|+ |
| | |
| | |
+|-|+ |
| - | |
| | |
Tube 2 | | |
| | |
| - | |
+|-|+ |
| | |
N o----------------------+ +-----+

2.) Try using your approach with both starters, but attach a much smaller
cap (0.1 - 0.4? uF) in parallel to one of the starters.

Note that both options are non-standard. In the first case some tubes may
not start while some will. If you get them started, use this solution, else
try the second one. In this case, whether the tubes start will depend on the
value of the capacitor. Use the smallest possible, just enough to make them
start reliably.

Dimitrij

 

[Rick]

"Rick" <KilledBySpam.com> wrote in message



Your approach is generally safe, but it could lower the lifespan of the tube
with the cap.

The problem seems to consist of wrong starters. You will need some that can
act reliably at 110V, not the ones for 220/240V. The starters often have a
small cap inside (some nF only), so the 2 caps form a 1/1 voltage divider
and each starter gets half the mains voltage when the circuit is switched
on. The starters must be able to handle this voltage, else the tubes won't
power on.

The correct solution would be 2 new starters, but you may want to try one of
the following 2 options. None of them is really optimal, but they may be an
alternative.

1.) See Schematic (safe, but could take longer to start):

=======
L o--------^^^^^^^-------+ +-----+
Ballast | | |
(Inductor) +|-|+ |
| - | |
| | +-+ Only One
Tube 1 | | |S| Glow Starter
| | +-+
| - | |
+|-|+ |
| | |
| | |
+|-|+ |
| - | |
| | |
Tube 2 | | |
| | |
| - | |
+|-|+ |
| | |
N o----------------------+ +-----+

2.) Try using your approach with both starters, but attach a much smaller
cap (0.1 - 0.4? uF) in parallel to one of the starters.

Note that both options are non-standard. In the first case some tubes may
not start while some will. If you get them started, use this solution, else
try the second one. In this case, whether the tubes start will depend on the
value of the capacitor. Use the smallest possible, just enough to make them
start reliably.

Dimitrij

Thanks for that, nothing I had read had mentioned different starters,
and it didn't even occur to me. It makes perfect sense though.

I'll try your option (2), I'll check my junk pile for some caps. I'll
probably end up getting some new starters though, next time I place an
order with Farnell or RS.

Thanks again,
Rick.