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Trying to Build a Spark Getter

  1. Jul 5, 2012 #1
    Hello,

    Recently I have been trying to build a spark getter. The idea is that a high voltage is applied to a capacitor consisting two titanium plates, once the breakdown voltage is reached, a spark is caused, and small particles of titanium (our getter) come off the anode and the cathode. I currently have a neon sign transformer as my power supply, which outputs 6.5 kV and 30 mA at 38 kHz (AC). If i simply attach both ends of the transformer to the two plates of titanium, it creates a seemingly continuous arc, which unfortunately does not remove much material.

    In a previous model of this spark getter (this time using DC, at 5 kV) I placed another capacitor (built out of aluminum foil with a sheet of glass as the dialectic) with a capacitance of 2.5 nF in parallel to the titanium plate spark gap. After it was attached, the ark was no longer continuous, and instead consisted of stronger burst sparks. This is because the capacitor in parallel to the titanium plates would build up charge, then as the titanium plates sparked, the charge would flow through the gap in the titanium plates.

    The idea was to do the same to my new, neon sign transformer powered spark getter. The problem is that even though the titanium plates create an arc when they are connected to the transformer, one the capacitor is connected, there is no longer an arc or any sparks. It seems that if a capacitor with a smaller capacitance is used (around 74 pF) small sparks rapidly appear if the gap between the titanium plates is shortened (though they are much too weak). Though capacitors with larger capacitance do nothing.

    Any ideas as to why attaching a capacitor in parallel to my titanium plates kills my sparks?

    Thanks in advance.
     
  2. jcsd
  3. Jul 6, 2012 #2

    NascentOxygen

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    Staff: Mentor

    If the neon sign transformer is AC, although it is adding charge to the capacitor during a quarter-cycle, it then removes it as the AC changes polarity and adds charge of opposite polarity, then removes it .....

    Charge never gets a chance to build up.
     
  4. Jul 6, 2012 #3

    CWatters

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  5. Jul 7, 2012 #4

    Philip Wood

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    Gold Member

    Following on from nascent oxygen's post, I'd guess that the time constant (RC) of the RC combination of capacitor and internal resistance of supply is considerably greater than [itex]\frac{1}{38000}[/itex]s, the periodic time of the supply voltage.

    Incidentally, where do you get capacitors that can stand such a high voltage?
     
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