Preventing electrical backflow

  1. I have heard that there is a device(s) that will ensure that electricity can flow only one way and not reverse. If this is correct I would like to know what it (they) are. I have also heard that a capacitor has this ability and would like confirmation or correction.
    Thank you
  2. jcsd
  3. Bobbywhy

    Bobbywhy 1,864
    Gold Member

    No, not a capacitor.

    A diode acts exactly a "one way valve". It allows current to flow in one direction, and not the other. Look up "diode" on Wikipedia.
    1 person likes this.
  4. will a spark gap do the same thing?
  5. nsaspook

    nsaspook 1,341
    Science Advisor

  6. what i was thinking was having one side of the wire connected to an electrical ground, put in diode, wrap the middle of the wire around a pvc pipe, and end the wire in a spark gap to a wire that will return to the electrical ground. after that i will run a round magnet though the pipe. will this make a spark (at the spark gap)?
  7. Bobbywhy

    Bobbywhy 1,864
    Gold Member

    I do not think your apparatus (as I visualize it) would generate a spark gap. But, if you can make a clear sketch and or diagram, showing all the elements and how they're connected it would be possible to give you a "yes", "no", or "maybe".

    Steven, and you might also try to Google search for: "spark gap generator with magnet" and similar search phrases. Often there are Do-it-yourself projects for just what you're asking about.
  8. example

    ...................return wire
    ________->-________()()()()()()()____! spark gap
  9. If you induce a current (with your magnet) in an inductor (your coiled wire), you will be able to generate some voltage across the inductor. That voltage will depend on the inductance of the coil and the field density and rate of change you can achieve. If you are able to get a large enough voltage to overcome the breakdown voltage of the air between the end of the inductor and ground (your spark gap), you will push some electrons across the gap (maybe enough to get a spark). The diode is not necessary unless you are trying to charge something (like a capacitor) with several cycles of the system or prevent it from working in reverse, and at the voltages that will produce a spark, a single diode is not likely to have a reverse voltage that provides adequate resistance to reverse current flow. The dielectric strength of air is about 3 million Volts per meter so you will need to produce at least 3000V to make a spark across a 1mm gap. Using a 15000V neon sign transformer I have made some nice Jacobs ladders starting at a gap of about 4mm and breaking at a gap of about 100mm after a 1m climb.
  10. My point is not a visible spark (not that that would be bad) but rather any electric flow.
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