Cold Plasma Circuit

Discussion in 'The Projects Forum' started by ablaty, Nov 5, 2009.

  1. ablaty

    Thread Starter New Member

    Nov 5, 2009
    I am working on a project to make a cold plasma for my Physics class. A cold plasma can be created by running a high voltage, high oscillation current through a wire. I found a proceedure online I completed the circuit and hooked it up to a commercial 24 volt 3 amp power supply. I turned it on and it produced a plasma for about 20 seconds, but then it stopped working and the power supply started making a sound (My instructor said it sounded like it was overexerting). I turned it off, and I noticed that the IRFZ 34 Mosfet chip was extremely hot. Since then, I have not been able to get it to work.
    Since then, the power supply has been acting kinda funny. Whenever i try to power the circuit, the light on the power supply does not light up, and the power supply makes the noise I mentioned earlier. To Troubleshoot, I measured the amps that the circuit was drawing, and found out that it was over 5. I disconnected the circuit and turned the power supply back on, and the power supply seemed to be working fine (No noise and the light turned on).
    Because of this, I figured that the Mosfet chip overheated and created a short circuit(The only resistance through the Mosfet chip section of the circuit is an ignition coil) so I replaced it with a new one.
    I reconnected the circuit and turned it on, and it acted the same as with the old chip (Power supply light off, but making groaning noise, and no plasma). My instructor recommended replacing the Diode, which I did today, but that didn't change anything.
    So basically I'm not sure why the circuit isn't working. I figure something burned out, but I'm not sure what.

    Information that may be useful------------------
    When it was working, the circuit produces a high pitch sound, but it no longer does.
    The Mosfet chip is only rated for 20 volts, but 24 volts were going across it(thats what the instructions called for)
    I don't think the power supply went bad because it seems to be working fine when it is not connected to anything
    Other than the mosfet chip, there are resistors, a potentiometer, caps, a voltage regulator, and a 555 chip. I doubt any of those would have burnt out since they all see pretty durable and shouldn't have received any unsafe voltage.

    What most likely went wrong with the circuit? By process of elimination, I figured that the 555 chip must be burnt out, but I think those chips are pretty tough.
    I added a heat sink to the Mosfet chip, should that keep the mosfet from burning out again?
    I still have the old Mosfet chip. Is there any way to tell if it actually did burn out?
    Is the power supply still good. When connected to broken circuit, it makes a groaning noise, and the light does not go on (It is pushing over 5 amps and the voltage is about 14 volts instead of 24). It seems like there is a short circuit in the circuit, but it looks fine when it is not connected to the broken circuit, so I don't think that is the problem

    If you have any questions about my circuit, just let me know and I'll post more info

    Thanks So Much for taking the time to read this!!
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
  3. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
    The JLN Labs page is another overunity site, it's chock full of crap and non functional designs. Lots of fun.
  4. JDT

    Well-Known Member

    Feb 12, 2009
    555's are not tough. I once made a circuit that had a 555 and a few 4000 series CMOS logic chips. I accidentaly powered it from 24V. 555 popped, CMOS survived!

    If you get your power supply going again, I would definitely have some filtering and transient absorption between the power supply and your plasma circuit.
  5. tkng211

    AAC Fanatic!

    Jan 4, 2008
    1. Remove the FET from the circuit. Use an analogue Ohm meter to measure the resistance between the 'D' and 'S' terminals (with'G' shorted to 'S' or leave 'G' open), if the reading shows a very low resistance (less than 100 Ohm) it's burnt.

    2. Connect the power supply to the circuit without the FET , check if the power supply works properly.
    If so, use an analogue voltmeter to check the voltage readings of 555, pin 8 should be approx.12Vdc and pin 3 should be approx. 6Vdc. If that's the result, it tells the only burnt part is the FET.

    since you are using 30V for VDD of the FET, the FET should have a Drain voltage rating of >=60V.
    I believe the ignition coil you are using is rated for 13Vdc (in cars) you may need to connect a current limiting resistor to limit the current if 30Vdc is used. Besides, better check on the primary current of the coil to determine the current rating (with margin) of the FET. The insulation between the primary and the secondary windings of the coil is also important cuz it may cause damages to other parts in the circuit.
    Last edited: Nov 6, 2009
  6. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    The internal resistance of a plasma is HIGHLY variable, depending on pressure and temperature. Without some current limiting device, once it's "lit" there is essentially a dead short throough the plasma. I'd try it again, using perhaps 1 megohm of resistance in series with the transformer secondary.

  7. ablaty

    Thread Starter New Member

    Nov 5, 2009
    Thanks for all the help. It seems like the general consensus is that I need to add something to my circuit to protect it from the ignition coil. I replaced the 555, and the circuit still didn't work. On Tuesday, I will check the voltage on the 555 pins like tkng211 suggested.

    I ended up starting from scratch and building a completely new circuit though, and that worked.

    I am thinking that the easiest way to figure out what is burnt out on the first circuit is to disconnect the ignition coil from both circuits (this will prevent the short circuit on the board that does not work), then just measuring the voltage drop across each component, and once I find something that is different between the two circuits, I will know what is burnt out. Could disconnecting the ignition coil make one of the components blow out though?

    Thanks again,
  8. Duane P Wetick

    Senior Member

    Apr 23, 2009
    It seems like the HV discharge should be referenced to the plasma and not the +30 vdc source. It can go either way, you know, and it will take the path of lowest resistance, unless you direct it. I think this event is what caused the 30V supply to shutdown. Maybe it has recovered...maybe not. Check it out. Also some LV mov's connected around the low voltage side will keep things alive. Make sure you use HV wire (60kV) around your plasma tank, and keep all circuitry well clear.

    Regards, DPW