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Lighting strings of T5 lamps with a NST

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klugesmith

Sun Nov 26 2017, 09:25PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

The overhead fluorescent lamps where I work are being replaced with LED units that fit the same sockets and same ballasts. I could get more than 100 used T5's, standard 1163 mm length including pins.

That inspired some ideas for lighted holiday decorations. I took a 15 kV NST to the temporary pile of retired lamps, and had no trouble lighting a jury-rigged string of 8 lamps. Except for short, loosely-twisted wires repeatedly falling off of pins. Now working on a kluge to facilitate making a lot more temporary connections. Must be fast & easy to connect each lamp, and fast/easy/inexpensive to make the connector units. Pictures to follow.

Does anyone think a string of 20 lamps won't start? Peak output voltage of the NST should be more than 20 kV. No matter how it's divided up, at least one lamp will get more than 1000 volts, which I think will light even with cold cathodes.

For continuous operation, with few on/off cycles, what will happen to the cathodes if the arc current is much less than standard operation?

Any guesses as to the magnitude and frequency of arc current when a standard T5 ballast is used? I'm hoping to measure that on the bench tomorrow (Monday).

Patrick

Sun Nov 26 2017, 10:51PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

will the short circuit current hold the lamp on after the initial HV strike ? the nst may drop its voltage to prevent higher current.

radiotech

Tue Nov 28 2017, 07:47AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

I would avoid taking home old mercury bearing lamps until I
knew where and if they could be disposed of.

The lamps may light, but the NST is rated on how many feet of
neon tubing it can light.

And in the snow you don't want a string of them to part and arc.

I once (45 years ago) built a monster light display, consisting of
40 watt instant start fluorescent lamps connected in series. They were
driven by high power audio amps through transformers.

It lighted the valence of my firm's audio exhibition and was needed to last 2 weeks.

To get the color organ to really be impressive, it needed to hammer the bulbs.

It ate the lamps randomly. One of our crew was stationed behind the plastic panels,
with cartons (of 12) red,. green and blue tubes.

Twas a fiasco. And the service division had to distribute (hide) the cost
of all those odd lamps. But there were compliments on the display.

Don't set fire, or electrocute birds!

klugesmith

Wed Dec 13 2017, 08:32AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

klugesmith wrote ...
Now working on a kluge to facilitate making a lot more temporary connections. Must be fast & easy to connect each lamp, and fast/easy/inexpensive to make the connector units.

Finally got that one done. Fixture holds up to 20 lamps in a horizontal plane. Lamps are simply set in place, with the pins at each end resting on an insulating strip that supports half of the lamp's weight. Lateral positions are controlled by a vertical spacer pin between each pair of lamps. Bits of aluminum sticky tape, fixed on top of the insulator, form the connections on each end.

On the first attempt, with only six lamps, there was an unwanted arc between metal sleeves, leaving two lamps dark. Would I need to make new connector strips with wider gaps? A simple experiment was to skip alternate sections at each end, leaving huge gaps. That led to discovery that one tube was bad & wouldn't light at all. After replacing that one, the string of six lit up just fine. So I cut more tape, applied the other 12 or so shorting strips, and lit 20 lamps on the first try. Altogether, about 23 lineal meters of luminosity -- at about 50 degrees F (10 degrees C).

For later: measure the operating voltage and current. But not before outdoor Christmas lighting experiments. Big fluorescent stars, or icicles hanging from the eaves? As Radiotech warned: must not electrocute birds or start a fire. Good use for NST's _with_ Secondary Ground Fault Protection.

radiotech

Fri Dec 15 2017, 07:00AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

Some data from an old book on neon signs.

1513321185 2463 FT180911 Neon Signs Miller Fink First Ed 1935 Lindsay Reprint

1513321185 2463 FT180911 Neon Signs Transformer Usage Fink Miller

klugesmith

Fri Dec 22 2017, 08:26AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Thanks for sharing the practical neon tables, Radiotech.

I had some time to play this evening, and made a "medium size" star with primitive support & connections.

That after too much time on the computer, figuring out how flat one could make a pentagram out of rigid straight bars. The symmetrically overlapping strokes in popular images are, I think, the worst option for flatness.

There are three other topologically unique crossing orders. The one which looked most promising, while playing with soda straws, is thicker than 2x the tube diameter (duh!), but less than 3x.

Until computing segment length ratios, and seeing 1.618 everywhere, I'd forgotten about the close association between pentagrams and the Golden Ratio. Then when I tried to approximate the lengths with small integers, the progressively better "close fits" were all numbers in the Fibonacci series (as Dr Slack well knows). 8/5 is good, 13/8 is better, and 21/13 better yet.

Tonight's tube ends are mechanically connected with rubber doohickeys cut from a bicycle-tire inner tube. Electrically, thin stranded wire is held onto lamp pins with bits of clear PVC tubing.

Patric

Fri Dec 22 2017, 09:30AM

Registered Member #2899 Joined: Wed Jun 02 2010, 06:31PM
Location: Deinze, Belgium
Posts: 255

I have put a Slayer Exciter under the table...

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