24kJ Capacitor Bank

The Leyden jar capacitor posted the other day fails to compare to what [FastMHz], one of the members over at the 4HV.org forums, has been busy building, a 24kj capacitor discharge bank. This capacitor bank will be configured for 4500v @ 2400uF and can be charged up slowly using microwave oven transformers. It can then release all its stored energy in under a millisecond through a triggered spark gap. This allows for some pretty big sparks as seen in this video, we are not sure about the laughing in the video maybe the power has gone to his head?


A bank like this can be used for a railgun, induction launcher, or exploding things in general. Coin shrinking and can crushing require much quicker discharge rates than what electrolytic capacitors are really capable of, and generally perform better with large pulse capacitors, however it will be interesting to see the final use for this potential energy.

42 thoughts on “24kJ Capacitor Bank

  1. While blowing pickles and potatoes up is fun, the 24kj bank’s main intent is induction launchers. Previously, I used a 3.5kj system to launch
    induction “rockets” with a 3.5″ diameter coil, as seen here:


    I’ve just built an 11″ diameter coil and should be able to send massive rockets up with this bank.

    The noise during discharge of that much energy sounds like a military sniper rifle. With this many lytics in an array, they are more than capable of large pulse operations as seen already.

  2. ok, newb question. I have around 2000 4.7uf 50v electrolytic capacitors. Could i (for ease of thought) say charge them all and link them in series to get 100,000V at 4.7uf? i’d love for somebody to point me to something i can do with them all. Thanks.


    1. Capacitors in series lose capacitance, sort of like how resistors in parallel lose resistance. You would have a 100kV capacitor bank at 2350pF. Assuming you didn’t figure that out since you asked the question nine years ago.

  3. The induction rockets look pretty cool I wonder if the concept could be used in conjunction with normal solid or hybrid rocket motors.
    Of course the timing and ignition system will have to non electrical.

  4. I presume fastmhz is planning on mounting this within the trunk / passenger compartment of a car / van and mounting the spark gap assembly inside a sturdy semi-elliptical or parabolic waveguide. At that point he would have a directional EMP cannon that should be easily able to knock out a police vehicle’s *, leaving the officer behind the wheel only able to shake his fist and yell out the window as fastmhz cruises on away.

    Just make sure that waveguide is really of high quality; you wouldn’t want any back-scatter or nasty reflections coming back to you…

  5. dok, you should link them in parallel. Capacitors need to be in parallel to add like you are thinking. They add the opposite way of resistors. The equivalent capacitance of capacitors in series would be Ctotal = ((C1)(c2))/(C1+c2) start at one end and replace 2 with this equation then use that value and the next capacitor all the way till you only have one number.

  6. Maybe someone else can tell me why people do this or if anyone else is annoyed by this too.

    Why do you say 2400uf instead of 2.4mf? Same thing with wall adapters, its 1000ma why not just say 1 amp? We are using these suffixes for a reason right?

    I’m really just curious if there is a reason and if it annoys anyone else? Perhaps I’m just strange.

  7. I accidentally discharged 400uF @ 450V capacitor bank once. the EM pulse froze my Amiga 1200 at 2 meter distance and damaged hard drive, my PC was undamaged 4 meters away, my neighbours had their PC’s reset or frozen.
    if fasttmhz does not want EM pulse then he should put the capacitor bank in faraday cage and twist the discharge wires together.
    higher voltages should be better for EM pulse generators, lower for coil guns and can crushers.

    fastmhz, be careful with that, it can kill.

  8. “Why do you say 2400uf instead of 2.4mf? Same thing with wall adapters, its 1000ma why not just say 1 amp? We are using these suffixes for a reason right?”
    You are forgetting the bit about significant digits. 2.4mF is not the same as 2400uF. 2400uF should be written as 2.400mF which means you’ve actually spent an extra character just to talk in units which you then have to convert back to uF to make any comparisons anyway (there aren’t a lot of capacitors int he world that are even 1mF big).

    So, to answer your question, you talk about things in units of the significant digits. 99% of the time 134.567 amps will be written as 134,567 milliamps, and 134.567000 amps will be written as 134,567,000 microamps.

  9. @Sidusnare: using mF as a unit is confusing, because it has historically been used for both “millifarad” and “microfarad”.

    @Johnny: Ct = 1 / ( 1/C1 + 1/C2 + 1/Cn ) is mathematically the same, but calculating for a large number of identical capacitors is much easier; Ct = 1 / ( 1/C * N )

    Your method is also correct, and can also be simplified for identical capacitors:
    Ct = ( C ^ N ) / ( C * N )

  10. The discharge is too fast for a regular camera to do justice in slow-mo. He needs to contact the guys at the new TV show “Time warp” and see if he can get them to record it for their show at up to 20K fps.

    You’d have to guarantee not to EM blast the equipment though

  11. Yes, the kilovolts are needed because of Ohm’s law. 2.7v would simply heat the coil and very slowly discharge. The high voltage causes more current to be drawn, the discharge to happen much more quickly, and therefore the magnetic field to be much higher.

  12. @sieg – To calculate power of a capacitor, you take voltage and multiply it by itself, multiply the product of that by the capacitance in farads, and divide by two, to get the energy in joules.

    Simplified, this is V^2 * C / 2 = J

    V = Volts,
    C = Capacitance,
    2 = 2
    J = Energy in Joules

  13. I almost never reply anywhere, but I gotta say: This is the best discussion! It never gets into politics, grammar and all that nasty BS. Congratulations. I really like the confirmation of 2 = 2. Spectacular.

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