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d.i.y. 250 kV High Voltage DC Power Supply with Neat Trick for Switching Polarity

d.i.y. 300 kV DC high voltage power supply by David and Shanni Prutchi

High voltage DC power supplies are used by science enthusiasts for powering electron tubes and x-ray tubes, charging high-voltage capacitors, powering electrostatic “levitators”, etc.  Many of these power supplies use a flyback transformer to produce high voltage at high frequency (AC), followed by a “Cockroft-Walton Multiplier” to rectify and dramatically increase the voltage.

The Cockroft-Walton multiplier uses a cascaded series of diodes and capacitors to generate a high voltage DC potential from an AC input through a circuit topology that uses diodes to charge capacitors in parallel and discharge them in series.  The output polarity of the Cockroft-Walton multiplier depends on the way in which its diodes are oriented, so the output polarity (referenced to ground) of a high-voltage DC power supply is usually set during the design.

However, since some of our physics experiments require one or the other polarity, we build our Cockroft-Walton multipliers with an extra capacitor so that we can make our HV power supplies output either positive or negative high voltage referenced to ground.  The schematic for our “reversible” Cockroft-Walton is shown in the following picture (click to enlarge): Schematic of Dual-Polarity High-Voltage Cockroft-Walton Multiplier by David and Shanni Prutchi

If the high-voltage AC output of the flyback is connected to point “A” of the voltage multiplier, and point “B” is connected to ground, then the output at point “D” will be positive. If however point “C” receives the high-voltage AC, and point “D” is connected to ground, then point “B” will be negative.

As shown in the following pictures, the multiplier should be built on a piece of clean perfboard:

Circuit board of Dual-Polarity High-Voltage Cockroft-Walton Multiplier by David and Shanni Prutchi

Circuit board of Dual-Polarity High-Voltage Cockroft-Walton Multiplier by David and Shanni Prutchi

The circuit board is then suspended by nylon spacers inside a plastic enclosure (of the type used to store food):

Dual-Polarity High-Voltage Cockroft-Walton Multiplier inside plastic enclosure by David and Shanni Prutchi

Banana connectors are then installed on the plastic container and wired directly to points A, B, C, and D.  The connectors must be sealed very well using silicone RTV:

Banana connectors in Dual-Polarity High-Voltage Cockroft-Walton Multiplier by David and Shanni Prutchi

The connectors are then labeled as follows:

Labeling of Dual-Polarity High-Voltage Cockroft-Walton Multiplier by David and Shanni Prutchi

Labeling of Dual-Polarity High-Voltage Cockroft-Walton Multiplier by David and Shanni Prutchi

The plastic container should then be filled with pure mineral oil (may be purchased at a pharmacy) to completely submerge the multiplier circuit assembly, which prevents high voltage breakdown between components:

Dual-Polarity High-Voltage Cockroft-Walton Multiplier by David and Shanni Prutchi

You can use any high-voltage AC power supply to drive the multiplier. Our favorite circuit is the following DC-to-AC inverter (click diagram to enlarge):

High voltage AC driver for 250 kV DC power supply by David and Shanni Prutchi

In this AC power supply, a push-pull oscillator drives a TV flyback transformer from an old color TV (a flyback without embedded tripler). The well-known hack is that the original primary of the flyback is not used. Instead, new primaries are made by winding two sets of four turns each of insulated #18 wire around the exposed core of the flyback transformer. Feedback for the oscillator is obtained through an additional coil of 4 turns of #24 wire wound around the core:

High voltage flyback hack for 250 kV DC power supply by David and Shanni Prutchi

Inside chasis of d.i.y. 300 kV DC high voltage power supply by David and Shanni Prutchi

As shown in the picture above, we built the low-voltage DC power supply right into the chassis.  We vary the voltage using an external variac (not shown in the pictures).  In our power supply, 12 V applied at the input of the flyback driver produces around 250 kV DC at the output of the multiplier.  We have measured up to 300 kV DC at higher input voltages, but the corona and breakdown get very scary, so we haven’t tried pushing the limit.

UPDATE 2/10/2012: Please see the following two posts for additional information on building the resonant transformer driver, as well as on winding the primary for the flyback transformer:

http://www.diyphysics.com/2012/02/10/universal-resonant-transformer-driver-high-voltage-flyback-driver/

http://www.diyphysics.com/2012/02/10/adding-your-own-primary-to-high-voltage-flyback-transformer-for-resonant-driving/

The following YouTube video shows an early version of our d.i.y. power supply being used to fly an electrostatic “lifter” that Shanni built many years ago as a grade-school science-fair project:

In our d.i.y. book “Exploring Quantum Physics Through Hands-On Projects” we show many ways in which this power supply can be used to perform advanced physics experiments.

DANGER! Please note that this is a dangerous device! It produces high voltages which can cause very painful or lethal electrical shocks. In addition, spark discharges can be produced which can ignite flammable materials or volatile atmospheres. Remember that the capacitors retain charge long after the power supply is switched off.  Thoroughly discharge them before touching the high voltage rails!

 

Please visit www.prutchi.com and www.diyPhysics.com for other cutting-edge d.i.y. projects, and remember to check out our new d.i.y. Quantum Physics book:

 
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14 Comments  comments 

14 Responses

  1. […] today’s project on diyphysics.com, David Prutchi shows how to build a Cockcroft–Walton multiplier using a “ladder” of […]

  2. […] you have a project that needs a bit more than 3.3, 5 or 12 volts have a look at this Home Made 250 kV High Voltage DC Power Supply! Of course this isn’t your typical supply for the Arduino project sitting on the corner of […]

  3. […] use the flyback-driver circuit shown in our d.i.y. 250 kV DC power supply in many other of our setups, so we built a stand-alone universal resonant transformer driver.  The […]

  4. […] two prior posts show how to build very high voltage power supplies using flybacks from old color TVs.  The advantage of the method we use is that any flyback can be driven, […]

  5. […] power supply pool you may be thirsty for a bit more knowledge. Here’s a neat illustration of how to build a voltage multiplier that can output a positive or negative supply. It is based on a design known as the Cockroft-Walton Multiplier. It’s the add-on housed in […]

  6. Hypatia's Protégé

    Two suggestions:

    1) Regarding the Royer oscillator: Instead of 1N4007s you may wish to consider ‘fast recovery’ diodes…

    2) Regarding the Cockcroft-Walton cascade: Please note that the stress on the rectifiers is twice the peak excitation EMF — Hence, with the rectifiers specified at 20KV (as shown), the maximum input to the cascade should not exceed 10KV Peak (7.07KV RMS) — Corresponding to (Max) DC outputs or 99KV (as per the 5 stage cascade shown in the diagram) and 158KV (as per the 8 stage cascade shown in the pictorial).
    At the stated 250KV output, each diode is ‘seeing’ approximately 29KV… Depending on the manufacturer’s ‘safety margin’ this may pose a significant reliability issue…

    With constructive intent

    Best regards
    HP

  7. Jacob Shin

    What is the output (in kV) of the AC flyback power supply circuit that goes into the input of the Cockcroft-Walton Multiplier Cascade?

  8. Thomas

    A quick few questions.
    Your schematic is very nice. Thank you very much for your time, sirs.

    1. Are those 1N4007 diodes connected between the BASES and EMITTERS of each transistor? If so, is their purpose to protect the transistors and the rest of the power supply from high voltage kickback?

    (I’m only asking because on other flyback driver circuits that use a single transistor that I have seen, the diode employed for protective purposes is placed between the COLLECTOR and EMITTER, not the BASE and EMITTTER.)

    Source: http://www.instructables.com/id/2n3055-flyback-transformer-driver-for-beginners/?ALLSTEPS
    ———————————————————————–

    2. What is the kind of wire you are using for the primaries and feedback coil, and what is its topography? (Litz wire? Would single-core enamelled magnet wire suffice?)

    What I mean by ‘topography’ is as follows:

    Am I correct in assuming that each coil consists of 4 turns of wire for the first primary, and 4 turns of wire for the second primary, and then 4 turns of the smaller wire for the feedback?

    Lastly, is the feedback coil literally wound around ON TOP of the existing primary coils? Or are all three coils wound in descending order if you will, around the exposed core? (Thereby not sandwiched on top of each other?) What would be the differences in performance/functionality of the flyback between one of these winding styles VS the other? Why double-stack the feedback winding on top of the primaries like that… or don’t?

    Thank you, and warm regards.

  9. Thomas

    Oh, also, at what minimum frequency is this circuit expected to oscillate at, providing the flyback to be used is not the new style, but one of the large old style devices with the disc shaped, fat secondary?

    I am hoping for something over 5 kHz, if this can be determined.

    Thanks again.

  10. Thomas

    Anyone’s responses are welcomed at this point, just to gain clarity on how this works. I welcome the discussion.

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