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Large neon lamp connected on HV power supply

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medved

Wed Jan 24 2018, 04:38PM

Registered Member #4338 Joined: Sun Jan 15 2012, 10:19AM
Location: Slovakia
Posts: 21

Hi all !
I got to the big neon lamp and connected it to the HV power supply (AC 25,4kHz). At a certain value of voltage and performance, this phenomenon occurs as a video. There are moving holes in the plasma. Does anyone know what it is and why they are there? I can also influence them by hand - stopping holes or moving.

VIDEO

Photo

HV power supply:
IGBT half-bridge
Umax: 22,5kVp
f: 25,4kHz

Nik

Wed Jan 24 2018, 05:40PM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

I don't know why it happens but I have seen failing fluorescent tubes do the same thing.

medved

Wed Jan 24 2018, 06:14PM

Registered Member #4338 Joined: Sun Jan 15 2012, 10:19AM
Location: Slovakia
Posts: 21

When I plug it into the original Neon Sign Transformer (8kV), it lights up normally. Only after connecting to half-bridge power supply at 25.4kHz is this phenomenon occurring - when I slowly increase the voltage. When I exceed a certain voltage, it starts to light normally and the holes in the plasma disappear.

alan sailer

Wed Jan 24 2018, 06:57PM

Registered Member #59110 Joined: Mon Apr 11 2016, 04:35PM
Location: Camarillo, California
Posts: 74

medvid,

This effect is known as beading in the neon sign business.

Sometimes it's a bug and sometimes a feature. It's definitely a function of higher frequency AC transformers. I've seen it quite often when I am filling plasma tubes. It happens at lower pressures and changes as I sweep frequency.

I've read no explanation.

Are you using an old flyback for you HV supply?

Cheers.

medved

Wed Jan 24 2018, 07:43PM

Registered Member #4338 Joined: Sun Jan 15 2012, 10:19AM
Location: Slovakia
Posts: 21

Interesting. I use my own HV transformer + IGBT half-bridge.

primary coil: 17 turns
secondary coil: 1100 turns
ferrite core: 25x25mm

Photo - HV transformer
VIDEO - HV power supply

Sulaiman

Wed Jan 24 2018, 10:17PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

the beading effect has been noticed since Crooke's tubes etc.

I guess that the length of the plasma grows with voltage due to capacitance to the environment,
from the video I guess that the inner connection is more 'earthy' and the outer/helical terminal is h.v. a.c.

StaticBuildup

Fri Jan 26 2018, 12:20AM

Registered Member #61695 Joined: Sun Jul 16 2017, 11:22PM
Location:
Posts: 31

Those are striations, they sometimes happen in gas discharge tubes. The physics behind them seems to be something to do with oscillation and waves.

Link

I like them, it is like a train of plasma moving along. Even better when you can change the movement by touching it. :D

alan sailer

Fri Jan 26 2018, 11:19PM

Registered Member #59110 Joined: Mon Apr 11 2016, 04:35PM
Location: Camarillo, California
Posts: 74

medvid,

Do you have any details about your winding/insulation technique? Does the coil appear reliable?
Heating effects? Electrical specs ie voltage, frequency etc?

I had a huge issue finding HV AC coils for my plasma tubes, surplus color TV flybacks solved my problems. But I'm
still interested in roll your own solutions. My one try worked great for about five minutes....

Cheers.

alan sailer

Sat Jan 27 2018, 12:51AM

Registered Member #59110 Joined: Mon Apr 11 2016, 04:35PM
Location: Camarillo, California
Posts: 74

My own limited observations are that the bead (or striations in the science world) tend to be stationary
in the case of DC excitation and move with AC excitation. In the case of AC I have been able to change
both the direction and speed of the beads when using a variable frequency power supply. The spacing
stays constant to first order.

If you search on glow discharge striations you will run into a boatload of papers both recent and old
which leads me to believe that the subject still hold mysteries.

My own hand waving explanation of the beads moving with AC excitation is that the beads have a natural
spacing due to electron capture by the atoms in the gas. When the voltage is DC this leads to an
equilibrium and the beads stay still. When the excitation is AC, this frequency mixes with the natural
spacing and causes the beads to march/

Cheers.

medved

Sat Jan 27 2018, 07:02PM

Registered Member #4338 Joined: Sun Jan 15 2012, 10:19AM
Location: Slovakia
Posts: 21

alan sailer

try to look here, it's not in English but I have photos of the current secondary coil at the bottom of the article
http://www.vn-experimenty.eu/index.php?stranka=homemade_vn_trafo

and here is the article HV power supply
http://www.vn-experimenty.eu/index.php?stranka=vn_zdroj_IGBTpolomost

in this topology half-bridge and this own HV transformer, I can....
20kVpeak - permanently
22,5kVpeak - still OK, but the corona is formed between the layers
25kVpeak - shortly OK, but no more! (or use oil for transformer and 25kVpeak will be OK!)

frequency of power supply: 25,4kHz
resonant frequency of HV transformer: 50,8kHz

some information of HV transformer:
insulation: 2x layer - transparent foil for laser printers + for fix insulation tape
for 1 layer: 50 turns (30-50 turns, 50 turns is max (corona))
layers: 22
turns: 1100
my ferrite core: 25x25mm

... and thank you all for interesting information! :)

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