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Plasma Tube Driver Troubles

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alan sailer

Mon Aug 08 2016, 03:09PM

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

I've been working over the last half year to fill and seal some small plasma tubes and have been getting closer to making a good tube/globe. Of course one of the engineering problems to solve is making a dependable high voltage/high frequency driver for the tubes. I adapted the driver from an old electronics article that uses two mosfets driven push pull. For the output transformer I am using a CHIRK flyback.

Until last night I though the circuit was a keeper but suddenly the thing died. When I was checking for the problem I noticed that the transformer was really hot. I had used the driver for about 20 hours total, usually in short intervals to test various plasma tubes but I have had it running for hours at a time with no apparent problem.

My question is nebulous but here it goes. I want to find a flyback transformer that it rugged and that I can understand why it works so that I can make a reliable power supply. When I look at the specs for the CHIRK and other transformers the numbers are always really vague. For example the input votage is 20 to 800 volts. The power is 40 to 80 watts. I was running 12 volts and a a maximum of 48 watts. So why did it overheat and blow up? Hell if I know.

When I started this project I bought some flybacks from some one on this site who felt that they were an improvement over something called a Fiddy flyback. It blew up before I could even try running a plasma tube. I was using the same MOSFET circuit and power supply (12V/48watts).

I'm not trying to get some really exotic outputs. 10-20kV at tens of kHz and about 40 watts is all I want. But I want it to run for years without needing a transformer replacement.

It seems like the only way to work with these flybacks is to run one until it dies and then try to guess why it died. Which doesn't work for me. I get the feeling that you can have a circuit that looks like it is working but secretly the inside of the flyback is corroding away due to corona and sudendly, lights out.

Any advice on this subject is welcome. I have to say that I am pretty discouraged at this point.

hen918

Mon Aug 08 2016, 05:20PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

You are blowing flybacks? That isn't good. I've given mine (I also have some of the "better than fiddy's" flybacks) some high power high duty cycle with the classic Mazzilli driver and they have been fine. So long as you don't run them at a too high a voltage they will work OK.

Could you link or upload the driver circuit? It might be giving the flyback too many volts per turn.

If the flyback is actually being driven in flyback mode, then a lack of output diode and filter may be causing the peak voltage to swing high.
Does it have a safety gap to arc over when it isn't being used and keep the output voltage down?

alan sailer

Mon Aug 08 2016, 06:47PM

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

Thanks for the reply. I am not sure how to download the schematic. The article that the driver is based on is titled as below.

Aug 1997 ELECTRONICS NOW (magazine), Build the Poor Man's Plasma Globe, by R. Iannini and Marc Spiwak. Use a decorative spherical light bulb and a 12v power supply based on FETs and a flyback xformer.

I was able to down load the article using this link.

The flyback (and I'm pretty sure that it is not operating in flyback mode) is a CHIRK transformer purchased from Images Scientific and is the part number HVT-01.

The same circuit(with a different flyback) is sold on the Information Unlimited website and is called the PVM-12.

I was talking with Carl Willis (fusor and plasma tube maker) on the phone this morning and he may have given me a possible reason for the damage. I have been tuning the circuit (sweeping frequency) to set the voltage at a good level for each plasma tube. When I tune I often pass through the resonance of the flyback. The Circuit gets really angry sounding for a brief moment until I pass through the resonance. I don't operate at this point but maybe the resonance puts a strain (over voltage) on the transformer, creating a small carbon track which then expands during normal operation. That would explain why the transformer was so darn hot after it died because all the DC power was being dissipated in a "low" resistance path inside the unit.

Does this sound like a possible reason for the short lifetime of the transformer?

zrg

Mon Aug 08 2016, 07:03PM

Registered Member #4762 Joined: Sun May 06 2012, 05:59PM
Location: Russia
Posts: 93

CHIRKs are a bit of crap. Purchased about 40 flybacks of theirs, and they keep to blow up. Wrong design lead to overheats and massive corona from cold secondary end to hot one.
I got just the same application (plasma tube driver) and looks like I''d have to design my own made-to-order transformer with large ferrite and custom secondary.

>I was talking with Carl Willis (fusor and plasma tube maker) on the phone this morning

Maybe you can give me in PM some kind of his contacts (not phone or facebook) if possible? Skype, email, telegram etc. I have an interesting plasma tube specimen to discuss, and he doesn't answer youtube messages, which are the only contact of his known to me..

Here's the plasma tubes, btw.

alan sailer

Mon Aug 08 2016, 08:13PM

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

zrg,

If you have any recommendations of a better flyback I'm ready to try it. I'm finding this whole all high voltage/high frequency area frustrating as hell. As I mentioned before, the only time you know your circuit is having a problem is when it dies. And I never get any good knowledge when it dies.

Also I want to note here and now I have zero (maybe negative) interest in doing any of this for the purpose of selling anything. I just want some pretty plasma pieces. If you or Carl had been able to sell me some tubes/globes/etc I wouldn't be trying to make the crapping things myself.

I couldn't buy them so now I'm driving myself crazy trying to build them.

I'll send you Carl's Email.

hen918

Mon Aug 08 2016, 09:08PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

According to the pdf, the driver is designed to operate at the resonant frequency of the flyback. With no load on the flyback the secondary voltage will rise above the insulation breakdown voltage. This seems a very poor design, as the over voltage will kill the flyback, as Alan said, this is causing corona to eat away the internals of your flyback.

Try turning your frequency down to 1/2 the resonant frequency (about 35kHz) using the potentiometer in the circuit. This should be much better for the flyback. The potentiometer should have a resistance (you will need to take it out of circuit to measure it) of about 120k ohms at this frequency.

alan sailer

Mon Aug 08 2016, 09:19PM

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

hen918,

Thanks for the analysis. I will try and set the resistor tuning so as the avoid the flyback resonance. The total resistance at this point is 16.5kohms and the resonance is at nearly the midpoint. So if I add another ~10kohm I should be able to tune without hitting a peak.

Although according to zrg I'm doomed becasue I'm using the Chirks. The resonant frequency is at about 25kHz. I may try running the transformer at a much lower voltage to study the resonance without harming the output coil.

We shall see. I have five of the things so I might as well try them out some more.

Conundrum

Tue Aug 09 2016, 06:34AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059

Oil?
I heard that vacuum pump oil works well if everything is well sealed.
I did run into a similar problem when running a TV flyback in centre negative mode (series) and it arced to the core which ruined it.

alan sailer

Tue Aug 09 2016, 03:55PM

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

Oil would be great solution except I have no idea where to find an un-potted flyback coil. The oil needs to penetrate the coil winding's in order to work.

Any solution to this issue is something I want to be able to replicate. I want to have several plasma/glass running at the smae time so I need to have several power supplies.

Cheers.

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