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Tesla coil with 555 timer troubleshooting help

  1. Jun 28, 2012 #1
    I attempted to build a tesla coil with a 555 timer but seemed to have failed some where.

    Perhaps you could take a look and give me some hints on what to try in order to make it work. I attached some pictures as well.

    I made the secondary coil on a 1/2 (.875 OD) pvc pipe with a 10 to 1 ratio (8.75 inches tall) with 28 gauge Magnetic wire.

    The primary i only free handed it, and perhaps that's where i went wrong, but did 9 large coils slowly geting larger as it went up.

    I made a 555 timer based schematics found at tacashi.tripod.com. I tested battery voltage when on (drops from 12 to 11). I didn't get any voltage comeing out though. Is it possible i reversed the source and drain? The trainsiter gets really hot in the few seconds i run voltage. I am not sure how to test the square wave so i don't really know.

    To be honest i am not 100% positive i installed the transistor properly either. I looked up npn mosfet transitors and read about the source gate and drain and attempted to figure out what E C B stood for.

    Here are more angles of the board

    Here is the schematic is used
    Last edited by a moderator: Apr 16, 2017
  2. jcsd
  3. Jun 28, 2012 #2


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    You can get the connections for your transistor on Google. (www.google.com) You can get them without paying, so, if you are asked for money, go to another site..

    Then, MAKE SURE your circuit is correct. You can do that better than anyone here.

    Then post your actual circuit as a circuit diagram, not just a picture. If you made up the circuit, you should get a proper one from on Internet and copy that.

    From the pictures, though, it seems there would not be much coupling between the primary and secondary of that transformer. Maybe the primary winding diameter could be reduced and the coil wound on the low end of the secondary.

    Also, the frequency of the 555 will have to be adjusted very carefully to get resonance in the secondary. This will happen at only one exact frequency.

    It is possible that your transistor is already blown up. Most multimeters have transistor testers in them, so you could try that.

    lots of luck.
  4. Jun 28, 2012 #3
    I did google the transitor and connected it based on what I found. I also tested it with a multimeter and it seems to be fine. If I put a meter on the output I should get voltage right?
  5. Jun 28, 2012 #4


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    If you use the AC voltage range of a multimeter, you might get some reading, but this coil will resonate at 50 KHz or higher and the AC range on some multimeters will not work at these frequencies.

    You really need access to a signal generator and an oscilloscope to adequately check the resonance of this coil.

    A signal generator is calibrated so that you will get an exact frequency your 555 oscillator has to achieve.

    Have you tried looking for practical Tesla coil sites on Google?
    I have seen some in the past which gave very exact details on making these coils and some pretty spectacular pictures of them working.
  6. Jun 28, 2012 #5
    I did. Most of them were about traditional tesla coils off 110 and a spark gap. I am trying to make dc work with a square wave.
  7. Jul 1, 2012 #6
    Keep in mind the reason they use 110 volts and spark gaps is that 555 and MosFet devices are very easy to kill when subjected to high voltage or high current, well, just call it high power.

    If you manage to run a current through the primary coil, it will cause a magnetic field which will induce a current in the secondary coil which will generate a magnetic field in the secondary coil. When the current to the primary coil is removed the secondary's magnetic field will collapse and in that collapse will induce a very high voltage in surrounding coils, like your primary coil. In the case of a spark gap, no harm done, the primary just shorts through the gap.

    In the case of sensitive electronics the instantaneous current may exceed the devices specs. Since 555 produce square waves and if your MosFet has sufficient HFE, it will try to mimic that square wave.

    The coil will slow down the rise as current builds, so you will get a ramp of current in the primary. The problem is when the 555 trailing edge of the square wave causes the MosFet to stop producing current really quickly, well, the amount of voltage produced in a coil is dependent on the strength of the magnetic field and how quickly it changes. So your ramp up will not produce a lot of back feed into the primary, but the instant off could.

    Try testing your circuit with a switch instead of a transistor. Cause current to flow then remove that current from the primary. You should get a spark from the secondary when you remove the current to the primary. Then think about what you might be subjecting the semiconductors to.
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