SOLID STATE TESLA COIL WITH 555 TIMER
Please be careful: All of the dangers mentioned in the ssstc page are valid for this apparatus too. So be aware of high voltage. Please read additional notes concerning your safety given in the text below.
Single transistor flyback driver caused many problems due to it's operating principle. I received e-mails from people who were unable to get it functional even when they are sure that their flyback and transistor is OK. In addition, since it's resonance frequency is determined by every part of the system, when you try to draw an arc from the transformer, it changes dramatically in most of the cases. Just because the operating frequency is important for the safety criteria, (both for mine and power transistor's), I decided to make it run on a constant frequency and built up another simple circuit, trying to stay in the specified limits of the 555 timer.
Setting the operating frequency with an integrated timer is easy and practical. Following schematic is nothing more than the standard astable mode circuit design with a classic 555. It requires only two resistors and a capacitor to set frequency (with duty cycle of course) and another resistor to determine power transistor's base current, which you can find it's optimal value experimentally. I used 1K for R1, 2.2K for R2, and 10nF for C which made circuit to run nearly at 27 kHz theoretically, at %60 high to %40 low duty cycle. You can quickly calculate operating parameters from the resistance and capacitor values with a small program that I've written.
555 Timer based flyback driver
Values given for R1, R2 and C in this diagram are the ones used on my prototype. You may change R1 and use a trimmer instead of R2 to find an optimum frequency / duty cycle combination for your flyback. By changing C, you'll have the ability to use higher or lower resistor values, but do not prefer too low resistances (especially for R1) for not to overload 555.
Duty cycle for given values
Power transistor is not critical and any other may be used as long as it's characteristics are equivalent or better. Here are the technical datas for BD243C for comparison:
Bipolar NPN transistor : BD243C
Casing : TO220
Max. collector current : 6 Amperes
Max. total power : 65 Watts, while case is at 25 degrees Celsius
Transition frequency : 3 MHz
hFE (current gain) : 30 at 300mA (minimum value)
Following PCB design would make it easier to fit components
on such a small space. Print it at 300 dpi to match the right scale.
Otherwise you should manipulate it to be printed in your specific printer resolution. You may refer to my PCB Design Page for more details on how to create your own PCB's. Lines that I painted thick are essential to carry enough current to the flyback through the power transistor, so do not thin them if you gonna draw it by hand, just like I do... Plate them with a solder layer to decrease conducting resistance. You may download a TIFF file already set to 300 dpi, ready to print.
PCB design for 555 Timer based flyback driver
Here is the PCB completed and ready to run. Since there's no current limiter on transistor's E-C path, please double check the board and soldered components to avoid unwanted contacts. Do not forget to mount power transistor on a heatsink. A small aluminum plate would be enough. Remember that transistor's collector is also it's metal surface, so prevent short circuits.
Completed PCB and power transistor on heatsink
This is the flyback I use. It's much bigger than the tiny one used in single transistor driver experiments. I was unable to operate this one with a transistor at a safe frequency, so it's one of the reasons you are able to read up this page now :) You may notice there are seven cycles of copper wire winded as primary. This number of turns are resulted from my experiments, which is found as an optimal value for my flyback, while running at 27 kHz.
Flyback transformer used in experiments
Power up the circuit with 6 volts initially. If it runs without overheating you can raise it up to 12 volts. If everything is OK you may have such arcs like the ones below...
Arcs with flyback driven by a 555 Timer
You may notice that I've operated flyback in front of the computer recording photos, but this is a totally controlled case. I set the cables far enough from the flyback and also the computer's metal casing is closed, shielding inside. Camera is tested against interference by gradually approaching it to focus distance. Such an operation may harm your electronic equipment in a similar scene so take the risk yourself.
Since digital camera's light sensitivity is different from our eyes, the arc color looks wrong in taken photos. I managed to take more natural ones by adjusting posing time. Here are three arcs in bluish violet.
Arcs in the dark
The camera I've used is a parallel port one and has a very low transfer rate. In addition, I have to use it with my old 486, just because my Pentium's mainboard have a defective I/O IC and thus the parallel port is unusable. Frame rate and color quality of the movies are awful but they should be enough to demonstrate operation of the circuit. Clips are in Cinepak format so you should be able to view them without any problems.
This clip shows a typical arc formed by two copper wires. It is thin and has a color between blue and violet. My experiments shown that the arc is at a very high temperature, since it's a plasma in nature. This arc will burn whatever you bring in contact with it, only metals are survived due to their conductiveness. This leads to a conclusion that you should be very careful.
Drawing arcs from the flyback
Cinepak Codec, 316K, 9.4 Secs.
Amazing fact is that this powerful arc generating system does not hurt human, but only when handled right. Following experiments are very dangerous, and only shown here for informational purposes. Never try these yourself, especially if you've got little knowledge about electricity. I take no responsibility for your own acts.
Here is what will happen to your finger when it came in contact with one of the wires. Formed arc burns tissue rapidly in a moment! Please take a look at my burned finger and recognize the enemy well. What makes this situation dangerous is that you feel nothing at all till the burned hole move deep and reach the nerves and give a slight pain, which typically happens in about 2 seconds. This means you can severely burn a point in your hand (or wherever came in contact) and cannot be aware of it. Same thing is valid for nearby objects, which are not living but may cause a fire!
Accidental(!) burning of finger
Cinepak Codec, 82K, 3 Secs.
But if I hold a piece of metal object and approach it to the wire, an arc will be formed but my fingers won't burn. This is done by the object, which distributes current through many points of it's surface contacting with my hand. The current density is much lowered compared to the situation above where it was concentrated on a single point. This is much like Nikola Tesla's shows, but I feel that we're light years behind of his concepts ...
Drawing an arc with a metal object
Cinepak Codec, 172K, 5.2 Secs.
Now it's time to talk about the fancy experiment above. It's always caused people to have their mouth open, get amazed a lot and think much, when I introduce the phenomenon to them. Cause of their sudden mental shock was their belief, that higher voltages would harm you much more easily than lower voltages. In fact, it is the amount of current passes through your body that makes the damage, not the voltage. Voltage is only the description of "electrical pressure level between two points". In this circuit, the pressure level is so much (about 15.000 volts) that it can jump across air, but the current (theoretically electrons per time unit) flows through the wires is so low. In addition, the alternating frequency of the current is so high that your nerves are unable to detect it. It's much like you cannot hear high frequencies. Also it is stated that the current will flow through the outer layer of your tissue, not harming the internal parts of your body, at this much high frequencies. This is the well known Faraday cage effect. But in spite of these natural laws, I do not tell you to try this experiment yourself. Your circuit may not meet the specifications of mine and may be working at dangerous current output levels. Remember that it is exactly dangerous when you use a flyback that have internal capacitors and diodes. A capacitor is enough to store high voltage to be given back at practically zero resistance. I have NEVER tried to touch a such capacitor connected output and you should NEVER TRY IT too. Anything may act as a capacitor when connected to the high voltage output, for example a fluorescent tube or a neon lamp. Even your body is a capacitor when it's a part of any electric circuit.
Current passes through your body is capable of causing slight nerve damage. You may not feel anything disturbing but in fact the damage accumulates by the time. This is especially concerning your heart health, for which it is a complex electrochemical mechanism made out of fine arrangements of the elements. Current flow will cause an erosion on it's components that may lead it's beats to go out of sync. I do not know much about the self-repairing abilities of human heart but predict that this kind of defects cannot be recovered completely.
Concerning the dangers mentioned above, it is advised you
not to try coming in contact with the high voltage of the circuit. I neither
offer or encourage you to conduct such an experiment. Your life is so valuable
that it cannot be exchanged for a little sense of excitement. Take extreme
care in all of your works with electricity.
You can construct an Ion Motor with this generator. Please take a look at the Simple Ion Motor page.
If you haven't read ssstc page, may want to take a look at Simple Plasma Globe page.
E-mail me at: firstname.lastname@example.org
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