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Old 1st May 2018, 11:30 pm   #1
hannahs radios
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Default Neon signs etc.

Split from this thread:-

https://www.vintage-radio.net/forum/...d.php?t=146082


Hi. your signs you've got there look really cool one of them looks like a neon sign if it is how do you run it? I love lighting especially when it's proper lighting like filament bulbs, neon or fluorescent lighting.
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Old 2nd May 2018, 12:55 pm   #2
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Default Re: Neon signs etc.

Use a neon sign transformer that gives 10kV (or whatever) at 60mA limited output. They're still available to buy new.
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Old 2nd May 2018, 1:55 pm   #3
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Default Re: Neon signs etc.

Or use a car ignition coil, a 12V supply and an electronic driver cct (mark/space; freq). Here's one I prepared earlier...
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Old 2nd May 2018, 11:20 pm   #4
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Default Re: Neon signs etc.

Russell your home made neon supply looks like it works well, thanks for showing it. Could you put up a circuit diagram please?
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Old 3rd May 2018, 9:02 am   #5
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Default Re: Neon signs etc.

Quote:
Originally Posted by hannahs radios View Post
Could you put up a circuit diagram please?
I'll do a 'neat' one in due course. I claim no originality for the timer / PWM end. I built that, then stuck the parallel FETs and transorb and the other bits on from there. Two coils in parallel to give a low impedance with a CR snubber on there. It really does give a fatter spark than one coil.
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Old 3rd May 2018, 9:03 am   #6
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Default Re: Neon signs etc.

Apologies... It's upside down!
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Old 3rd May 2018, 10:10 am   #7
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Default Re: Neon signs etc.

Fortunately PDF has 'click to rotate' that actually works (doesn't always, does it!?)
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Old 3rd May 2018, 1:11 pm   #8
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Default Re: Neon signs etc.

Quote:
Originally Posted by russell_w_b View Post
Apologies... It's upside down!
Those neon tubes look lovely.

I'm surprised that you can get the IRF350 output fets fully enhanced by the driver when the load appears to be in the source, rather than the drain, but obviously it works just fine, it might just be the upside down circuit confusing me. Maybe they are not supposed to be saturating in your design anyway.

I got my first neon tube transformer when I was about 13 years old, I scavenged it from a discarded Milk Bar sign at the local dump. The transformer was an American Jefferson brand with crinkle paint, I think it was 7.5kV per side. The center tap was connected to the case/earth. The tube (argon) that said "milk" still worked. I used spark plug ignition wire to connect it up. But arcing the connections near the tube's wire fittings, perforated the glass and much to my horror, air leaked in, the color changed to a pink and crept along the tube, until it went out. After that I used the transformer for Jacobs Ladders and got numerous shocks from it, including one where the long Jacobs ladder wire came into contact with my cheek as it was swinging about and I got my head too close.

Last edited by Argus25; 3rd May 2018 at 1:33 pm. Reason: add a story
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Old 3rd May 2018, 2:11 pm   #9
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Default Re: Neon signs etc.

Quote:
I'm surprised that you can get the IRF350 output fets fully enhanced by the driver when the load appears to be in the source, rather than the drain
Does look a bit odd but there are separate supplies, the MOSFETs are in series with the 12V ans coil(s) so it doesn't matter.
 
Old 3rd May 2018, 2:15 pm   #10
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Default Re: Neon signs etc.

This thread ties in rather well with the fact that I am considering purchasing a set of discharge tube for the noble gases (helium, neon, argon, krypton and xenon - I'll pass up on Radon and Oganesson ) to demonstrate the various colours, and was wondering where to source appropriate power supplies for them.
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Old 3rd May 2018, 3:50 pm   #11
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Default Re: Neon signs etc.

Quote:
Originally Posted by Argus25 View Post
I'm surprised that you can get the IRF350 output fets fully enhanced by the driver when the load appears to be in the source, rather than the drain, but obviously it works just fine, it might just be the upside down circuit confusing me. Maybe they are not supposed to be saturating in your design anyway.
The coil works equally well in the live side as the cold side, and if I showed you the underneath of the heat-sink aluminium chassis, you'd see the felt pen markings where I have written so. I felt I wanted to keep the coils tied to ground; I had one or two swear-inducing belts off it when I first used it as a Tesla coil driver. Incidentally, I generally wrap a piece of nylon strimmer cord round my wrist, attached to the 12V supply clip - usually a car battery - so if bad things happen I pull it off quickly and automatically.

I originally had two 2N3055 bipolars in there and even banged hard-on, they got quite hot. So I put a couple of IRF350s in and there isn't a lot of power dissipated in them. We use IRF350s for the Marconi B6126 HF transmitter PWM switching stacks for grid and the screen of the TH555 switching valve where they are effectively switched-mode PSUs. Granted, they are on a blown heat sink, but there're six in series on a 1kV (and a 250V) supply. Mine seem to cope well and I can run more than 12V on the coil if I want to, but 12 - 14V seems just fine.
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Old 3rd May 2018, 6:02 pm   #12
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Default Re: Neon signs etc.

Quote:
Originally Posted by Argus25 View Post
Those neon tubes look lovely.
Thanks. They're 'skip rescue' ex-transmitter mast obstruction lighting tubes and I have eight of them. Strung along a piece of nylon cord they make excellent crimbo decorations. Looks a bit like a neon-filled gas-conductive inductor (low Q). I should try tuning one!
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Old 3rd May 2018, 6:18 pm   #13
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Default Re: Neon signs etc.

I found a neon sign transformer on a roof top in a rather rural part of S.Korea
It had been up there a long time, tube long gone, but it appeared intact with no cracks to let in moisture.

As it was looking very unwanted I was thinking to bring it home. I was put off by the thought of the weight and airline security. A great pity, it might have been fun.
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Old 3rd May 2018, 7:58 pm   #14
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Default Re: Neon signs etc.

Hi Dave, I did some work a while ago on Plasma globes (1mtr in dia). I used an old B/W lopt driven by a 555, works great and it can be tuned by altering frequency and m/s.
There is lots on the web about these and they also give details of colours with different gasses.
Old works on Geissler tubes, that were normally driven by induction coils are work reading.

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Old 3rd May 2018, 9:06 pm   #15
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Default Re: Neon signs etc.

Thanks Ed.
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Old 3rd May 2018, 11:38 pm   #16
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Default Re: Neon signs etc.

Quote:
Originally Posted by russell_w_b View Post
The coil works equally well in the live side as the cold side
Russell,

yes that is the great advantage of independent supplies for the driver and output stage, the load can be rotated around on either side of the battery and be grounded. But I think the the connection of the diver circuit to the fets might have an issue on the the pencil diagram, because the load voltage, developed across the ignition coil, ends up being in series with the fet's G-S drive voltage. So I have attached an amended diagram/suggestion.

Also when I was playing around with these fets ( I'm very fond of the IRF350)to drive ignition coils (for an automotive application) I found they were less prone to failure with a 12 to 20V G-S zener (in green on the diagram), so I got into the habit of using these in all my ignition coil driver designs, when I used the fet rather than a BJT.

There is really something quite magical and attractive about neon lamps, I have always liked the lyric in the Simon and Garfunkel; Sounds of Silence:

"When my eyes were stabbed by the flash of a neon light
That split the night"

They really do "split the night"

(Actually Disturbed do a brilliant cover of that song).

Hugo.
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Old 4th May 2018, 8:52 am   #17
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Default Re: Neon signs etc.

Quote:
Originally Posted by Argus25 View Post
So I have attached an amended diagram/suggestion.
Hugo: many thanks indeed - sounds like a plan to me! I'll modify accordingly.

Quote:
Also when I was playing around with these fets ( I'm very fond of the IRF350)to drive ignition coils (for an automotive application) I found they were less prone to failure with a 12 to 20V G-S zener (in green on the diagram)...
I'm afraid that's just laziness (and chancing it!) on my part when I knocked it up, not having a suitable zener at the time. So far, all OK but - there's always a but - I'll fit one as suggested. I've known others build far more complex circuits for coil-driving and they've been scuppered for want of a bit of protection. Thanks again.
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Old 4th May 2018, 10:25 am   #18
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Default Re: Neon signs etc.

Russell,

The best transistors I found for switching IGN coils were the MJ10014. 600V sustained collector voltage rating.

One big problem I found , while doing experiments, was what to do with the ignition coil secondary.

Left alone (no load) the peak voltage would peak very high and even jump out of the IGN coil output to the primary terminals. So I decided for my experiments it would be better to have the ign coil primary on its own. The attached photo shows a primary of a typical ign coil on its own (removed from a standard ign coil), no oil needed, just the Kapton tape.

One of the reasons why Lucas ran into trouble with many of their early electronic ignition systems, is because of what happened if the ign coil got left with its HT output disconnected. Under these conditions, the primary voltage on the coil can peak to over 800v (depending on the coil and the primary capacitive load or absence of it there). This destroys most switching transistors.

So after their disasters with the Opus ignition system, they looked to the US to save the day and use GM's HEI ignitions modules hidden inside Lucas AB14 units. But ironically the flagship of America's ignition module (The HEI module) still had failures with an open or disconnected ignition coil secondary. So, Lucas wised up, and incorporated a component that is now "unobtainium" ; the 350V stud mounted power zener (photo attached).

This completely solved all the problems of driving ignition coils with transistors, but it was an expensive part.

Later on some clever person decided that you could turn a transistor, or a mosfet, into an "active clamp". If you put a lower power high voltage zener diode from the collector to the base (or drain to gate) you could make the output device clamp off high voltage spikes and "save itself" from destruction. If you look at many modern IGBT's for ignition coil drivers, they have this active clamp built in to the device package.

Hugo.
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Old 4th May 2018, 7:17 pm   #19
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Default Re: Neon signs etc.

Lots of interesting ideas for driving neon transformers from DC.
Doesn't anyone have AC Mains anymore?
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Old 4th May 2018, 8:48 pm   #20
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Doesn't anyone have AC Mains anymore?
Oh, yes... I have a couple of 'Tunewell' neon sign transformers which deliver 60mA at 10kV but they aren't-half heavy! Unfortunately they are 110V primary voltage so I have to use a variac before them.
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