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Plasma Ball Power Supply.

    Once again the circuit I use is basically a solid state Tesla coil which is actually a fudged flyback transformer from an old television set.  The schematic I used is shown below.  The technical name is a Hartley Oscillator configuration of a Line OutPut Transformer (flyback) from fully rectified wall voltage.

Plasma ball driver schematic

    The circuit is basically 120 volts AC in a 25.2 volt step down transformer (which recently died and has been replaced), into a full wave bridge rectifier, and then a large filter capacitor, which gives me over 25.2 volts DC at just under 2 amperes in the primary side of the circuit WITH NO LOAD.  The capacitor is necessary as it charges during the peak of the AC cycle, and releases during the trough, smoothing things out nicelyThis voltage charges the primary coil and consequently the ferrite core of the transformer, which induces a charge in the "feedback" coil, which turns off the transistors. When the transistors have stopped conducting the power is rerouted through the resistors.  The EM field in the ferrite core then collapses with no charge to support it, which induces a large high voltage spike in the secondary coil in the reverse direction (basic laws of inductors).  After this happens, the transistor begins to conduct again because there is no longer any current in the feedback winding, which causes the DC input to oscillate AC, out from the secondary at a high frequency like 15-40 kHz, and around 10-25kV output.  Diodes can be used as a safty device to keep high voltage induced in the primary coil from frying my transistors (the system works without them, but they keep everything from heating up to quickly, which is good as during the development of this circuit, I fried a lot of transistors!)
    Here is a picture of my first system.  This flyback did not work because it's output was rectified which means it's output was DC, which won't work for a plasma ball unless it is pulsed (a pulsed DC circuit is harder to build, and the results are not as good, and ion migration can weaken the glass (kind of like an anode being degraded in an electroplating solution, but backwards!)).  The light emitted by the plasma is caused by electrons shifting orbits in the atoms, it is when they move that they emit light.  If the voltage flows continually, they will not have a chance to fall back and will not emit light after the first nanosecond or so.  When I tested this circuit on my professional globe a very interesting effect was observed, it looked like a pink aurora that spread across the glass, and moved away when one blew on it.  This was due to particles only being able to flip charges on the edge of the "cloud", blowing on it pushed the charged particles away so they discharged, and new charges could develop.  It was cool, but to dim to see with the lights on, so I dropped the rectified flyback (you can use them if you remove the diodes, but it isn't easy!).

rectified plasma globe assembly

So here is my new working but somewhat over-powered system. 
I finally got around to removing the flyback from the dead console in the garage and after winding my own primaries it works great!! (despite the unsightly rust spots, and great skepticism on my part!)  This flyback was used with a cascade, which is a fancy voltage multiplier that works with diodes and capacitors to increase voltage, cascades were commonly used in large old color TV's like the one I pulled this one out of.  The way I have it wired it doesn't need one, but it gives much greater output with one installed, but it is not suitable to drive a plasma globe in this state, as it seems to be rectified.  Modern flyback transformers often have a cascade built in, which is how they can get 25-40kV from such a tiny transformer.  Ideally one should try to get a transformer that doesn't need a cascade, but these are very difficult to acquire, and the ones used with an outside cascade will work, but will not put out much more than 10kV.

new plasma globe system

Here is my bridge rectifier, and step down transformer.   A while back, during a test of my globe, the transformer died (for referance when I say transformer I mean the step down transformer, and when I am talking about the flyback, I will say flyback),  they have a tendancy to burn out, as I have a tendancy to draw to much current from them, since this picture was taken, I have installed a 2 amp fuse, and reduced the number of transistors, and run it off the center tap ground instead of the other secondary (see the black wire).  This gives me 12.6 volts, which is a kind of wussy output for on my huge globe, the plasma is lousy with my less than ideal gasses.

rectifier and step down transformer

And here are my hand wound primaries!  I have since encased them in epoxy soon to increase efficiency.

Hand wound primaries

And here is an arc generated by the power supply to a ground wire (I apologize for the poor image quality, small arcs in dark rooms are hard to photograph, but just for reference that arc is over a 1 inch gap!).

arc power supply
 
     There are several preferred methods for constructing plasma ball power supplies, mine is the most popular, but not necessarily the best. It is true the Hartley Oscillator runs at resonance regardless of tuning so it is the simplest and most efficient method, but there is that problem of finding the ideal flyback, and winding your own primary and feedback coil (not always necessary, but usually).  What a lot of people use, is a square wave generator, like a 555 integrated circuit chip, which makes for a more complicated circuit, which usually whines loudly, and the worst part is when the load is changed (like when you touch the ball) the circuit is no longer in resonance, which you so carefully tuned it to be in, and output significantly drops.  Basically it works the same way as system with a feedback winding but the timer is set to oscillate at a fixed frequency, which is what trips the transistor.  The only advantages I can think of for this circuit is you can use an automotive ignition coil instead of a flyback (but contrary to popular belief, you can use a Hartley Oscillator for this as well, I'll explain in a moment) and you can (on a well designed system, with variable resistors) you can change the frequency to get better plasma (somtimes for best plasma, resonant frequency is not the best, I don't know why).  Another popular system used is the mosfet powered system.  I don't know what a mosfet is, except it is some weird kind of transistor, so I can't say much about it, except the systems I have seen are very complicated, and usually have a lot in common with the 555 timer systems, as an IC usually generates the frequency (I believe these circuits also usually have a variable frequency output, which is very good, because sometimes your transformer resonance output is not ideal for your gas combination, as I just said.)  Now hear this, modern flyback transformers must have the high voltage diodes in them bypassed to work correctly, and the intended voltage input is usually high (around 100-150 volts, which is how they make them so small) so to rig it to work one must (actually should, not really must) place an intermediate transformer between the flybacks origional primary winding (the highest resistance one in the coil), and your hand wound primaries.  Simply wind a bunch of turns on your secondary transformer, and several feed back turns (as if it were the flyback in my above schematic, except more turns) then wind many turns (10/1 is fine) from another wire, and connect it directly to the flybacks origional primary coil.  This will however cause the coil to operate at the intermediate transformers resonance, not the flyback's.  It would make sense to me, if a wire was physically grounded between the two transformer cores, that their resonance would be one in the same, but this is just a theory, I have not tested it, (or you could simply wind the feedback winding on the flyback core, this works, but doesn't seem ideal.  More experimentatiopn is necessary).  This system can also be used to drive an ignition coil with a Hartley Oscillator, I will try this soon to see what kind of results I get, after all, AIC's are relatively cheap at a junkyard, and have a good output, and I could build several power supplies cheaply, without spending another zillion years looking for another ancient flyback or winding my own! (in other words, more power, less money, and easy to obtain, does it make sense now?).  Actually I found several more good flyback, and the circuit ran for about three seconds and then died, I was not sure why, I thought it was the bridge rectifier, as it got really hot and melted the solder, but I replaced it with a half wave rectifier, and the thing still did not run I finally foud that I was having transistot failures, I must look into it to see what I am doing wrong.  I have lots of time and several flybacks here at school, so whoo-ah for me.
   
I have experimented with transistors, and found the display is jittery with some and it gets better if you use a slower one, but some give poor results (like three streamers, that crawl slowly along) but two transistors I ripped out of TV's gave me virtually identical results (on my professionally made globe) to the original power supply with 300mA input, except the streamers twisted and bent which was kind of cool, and they were ultra quiet, the fast one made a high pitch scream which has got to kill every dog for miles.  Unfortunately, my transistors started dieing (including my fast one), they just couldn't handle the amperage of the new transformer without a heat sink, but I got about thirty MJ15015, and I put four in parallel, and I installed the diodes to protect them from feed back induced from the high voltage spike, which helped a lot.  The MJ15015 is nice because it is quiet, but it seems a little to delicate, for one thing, you must use several in parallel to keep them from frying, and they get so hot so fast, that their frequency changes, completely altering the characteristics of your plasma (which is inconsistent at best anyway).  The advantage to using several transistors in parallel is they can handle the current with less stress, and they seem to have an amplifying effect, so the plasma is brighter, however their combined current draw is sucking the life out of my transformer (like a cheap sci-fi vampire), and overheating everything else.  I now use the famous 2N3055, which is the standby for hobbyists because it is reasonably powerful, and ultra cheap (for the price I paid for my original super powerful fast transistor the NPN NTE284, I could have bought 7 3055's).  The 3055 doesn't get hot as quickly (but you still need a heat sink) and it is more powerful than the MJ15015, the drawback is, usually it is "silent" with a frequency to high to hear, but unlike the MJ, a grounded arc does make some audible noise (My parents can't hear it, but my sisters and I can).  With two of these suckers, you can make a decent display, that doesn't kill the step down transformer (one would work with better gasses I would imagine!)  I also tried 3 tip 120 Darlington transistors, which worked decent but no better, and made a loud scream that even I could not tolerate (I havn't tried them with the low power, they may work better).  Now that I have my 25 volt transformer, my power supply discharges to the air like a tiny Tesla coil with half centimeter long arcs, and an arc grounded to the high voltage return (the equivalent of an RF ground, it is just the wire coming off the bottom of the flyback, from the secondary) or just some random grounded object, can be stretched out to an inch and a half, and looks like the thick plasma streamer coming off my Jacobs' ladder!

Home, Hobbies, Plasma Ball,

Scott Bogard. 2007