Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Best method to build a 30kv DC powersupply.

  1. Nov 30, 2006 #1
    I was initially going to use just an AC transformer and then some diodes to full way rectify and finally a capacitor on the end to convert to DC. This is probably unrealistic though due to the reverse biasing of the diodes.....

    Anyone have a good schematic for building s 25kv-35kv DC power supply?
  2. jcsd
  3. Nov 30, 2006 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The boilerplate first response has to be this one:

    Why do you want to build a 30 kV power supply? 30 kV is high enough voltage to kill you pretty much instantly unless only extremely small currents are involved.

    You will have a hard time with materials and devices which can handle such voltages.

    - Warren
  4. Nov 30, 2006 #3


    User Avatar

    Staff: Mentor

    Use a color TV flyback circuit. Oh, and be careful -- is your life insurance policy paid up?

    And I echo chroot's question -- what is this for? If it's for a research project and you have good experience working with high voltages, then using a color TV flyback circuit will probably work well. If you're wanting to make a home-brew Jacob's ladder and have no experience yet with high voltages, you're in for a shock.
  5. Nov 30, 2006 #4
    My current HV supply for my marx generator which is powering a TEA laser is very non precise on controlling voltage.
  6. Nov 30, 2006 #5
    I salvaged the goodies from every tv set that went to garbage. I don't do that any more because I have a drawer full of these suckers.

    Flybacks are very easy to hook up, and there are dozens of schematics on the net.

    Here is an excellent page with schematics. Flybacks are the cheapest way to get on 30 KV


    They produce very little current, less than a millamp if I had to guess, that's why they don't pose little or no danger to your life. I was shocked by them dozens of times, and it's quite soothing actually.

    But in certain circumstances, a capacitance can develop between the output of the flyback and the surroundings, resulting in an increased current. That's a little dangerous. You can tell if the spark turns from a purple color to a blinding white flash.

    Rule of dumb: 1 cm of maximum spark length = 10,000 Volts

    Hope that helps.
  7. Nov 30, 2006 #6


    User Avatar

    Staff: Mentor

    How much current does the laser require? As waht says, the color TV flybacks are sized for a few mA of electron beam current.

    Holy Zamboni, waht! :eek: You've been hanging around with Danger for too long.
  8. Nov 30, 2006 #7
    I work with high voltage (up to 400 KV DC) pretty regularly, and if you don't need much current you may want to concider using a Cockcroft Walton circuit. http://members.tm.net/lapointe/Cockcroft_Walton.htm This will give you an AC voltage that can be filtered to give you a DC voltage. This is going to be pretty expensive, but it should be stable.
  9. Nov 30, 2006 #8
    This Cockcroft Walton circuit will give you a full wave rectified voltage that will have an AC component to it. We have a filter on this to give us a stable DC voltage with little to no ripple in it.
  10. Nov 30, 2006 #9

    He's going to be shocked if he sees this.
  11. Nov 30, 2006 #10


    User Avatar
    Science Advisor
    Gold Member

    Too bad you need 30kV. I once built a HeNe laser using a neon sign transformer (9kV @ 18mA).
  12. Dec 4, 2006 #11
    Ideally you want a constant current PSU for driving your Marx. These generally have simple step-up stages to an intermediate voltage and then a switching rectifying unit in an Oil Bath. Look at ALE Technologies or Maxwell, they work the same, the schematics are available for both these systems, but the art is controlling the energy without them catching fire.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook