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.


  1. Theo V says:

    My God… I want one.

  2. Chris says:

    I wonder if this guy will make it into the Darwin awards (if he’s not careful!)


  3. Louis II says:

    damn… I was going to do this after reading up an a few of the layden jar configurations… doh!

  4. FastMHz says:

    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.

  5. dok says:

    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.


  6. FastMHz says:

    In reply to above, yes, in theory you can series all of them for 100kv…but how will you charge them?

  7. dok says:

    I was thinking charge them with some high resistance resistors between them then have spark gaps for discharged (they would act as high voltage switches) that should work right?

  8. sly says:

    charge them with a tesla coil *evil mad scientist laugh*

  9. fhunter says:

    to dok.
    No, you will get less capacitance.
    4.7uF/number of capacitors to be correct.

  10. Edward Nardella says:

    I’m impressed that he was able to build that without killing himself. I am off to look for a HOWTO for making those rockets.

  11. henk says:

    Is he high or something?

  12. BigD145 says:

    He seems mad with power, not high.

  13. mrbob1000 says:

    i must have on! it will go nicely with my potato cannons (only one of wich i use… in fact. my 4 inch internal diameter cannon i have only shot 1 time.)

  14. nitori says:

    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.

  15. lambda says:

    also tok, at the maximum voltage of 50V per cap, those caps will collectively have 23.5J of electrical energy across them.

  16. lambda says:

    Sorry, that’s 11.75J

  17. 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…

  18. Johnny says:

    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.

  19. SidusNare says:

    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.

  20. space says:

    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.

  21. Joey says:

    If you set this thing up with a big electromagnet at the end you could make a gnarly fucking EMP…

  22. “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.

  23. Sparky says:

    @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 )

  24. srilyk says:

    I, too, would giggle like a schoolgirl if I was discharging enough energy to kill me several times over. I mean… seriously, that’s some /energy/

  25. phorce1 says:

    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

  26. FastMHz says:

    Now there’s a thought…I’d *love* to see this thing fire in slow-mo recorded at 20k fps!!!

  27. witchdoctor says:

    +1 creepy high-pitched maniacal laughter

  28. fox64 says:

    I came

  29. isa de leener says:


  30. camel2 says:

    Couldn’t you have used like 2 supercaps of 3000F 2.7V instead, wich is also like 22~24kj ?
    Aren’t they fast enough to discharge maybe? Do you really need the 4.5kV?


  31. FastMHz says:

    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.

  32. aj-kun says:

    hate to be the one who pays his power bill

  33. jon says:

    where did u get those capacitors and how much did they cost?

  34. Sieg says:

    How can you calculate the power output (Joules) of any capacitor bank?

  35. NAPOLEON says:

    if there is any short circuit in one of the capacitor connected in paralle. will it affect the other capacitor?. if your ansswer is yes . how can one rectified the fault?.

  36. NAPOLEON says:

    what are the requirement need in construction of 33kv to 11kv capacitor bank.

  37. Christopher Karr says:

    @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

  38. FastMHz says:

    Volume 2 –

  39. Jay says:

    Wow, I want a back for the next 4th of July.

  40. jacob says:

    what model capacitor did you use

  41. Evo says:

    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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