votlage multiplier design questions

Discussion in 'General Electronics Chat' started by l0vot, Feb 17, 2014.

  1. l0vot

    Thread Starter Member

    Apr 29, 2013
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    I have some questions about voltage multiplier design:

    1. Is it beneficial to use caps that have twice the capacity but half the voltage rating of the next stage. Example:
    normal:
    stage1 .5MFD 10 KV, stage2 .5 MFD 10KV, stage3 .5MFD 10KV etc...
    VS
    stepped:
    stage1 1MFD .25 KV, stage2 .5 MFD 5KV, stage3 .25MFD 10KV etc...
    same thing with diode amperage/voltage ratings

    2. How do I determine the required amperage rating for the diodes in the multiplier if both the power supply and the caps are known values. Assume a direct short with 100% duty cycle
     
  2. ronv

    AAC Fanatic!

    Nov 12, 2008
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    You need to know the current that needs to be supplied by the multiplier and how much ripple you can tolerate at the output. Maybe a schematic of what you are looking at?
     
  3. l0vot

    Thread Starter Member

    Apr 29, 2013
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    <br />
    <br />
    large amounts of ripple is acceptable, I am looking for throughput, not stability. I am looking for information on how different configurations preform in general to help me design voltage multipliers that are suitable for whatever application I need one for. The current one I am designing is a dual half wave two-stage multiplier that should hopefully step a current limited MOT up to 16KV with a maximum power draw of 400W provided the MOT is of the 2KV variety. Currently 10nF caps will be used, but I think the first stage needs to use ~35nf caps to reach the 400W mark (but there are 2 caps/stage, so would 17.5nf work?). I couldn't find very much information on exactly how the cap size affects the amount amperage aside from basic impedance calculations, and i don't know how to find the impedance of the entire multiplier. Seriously, if anyone knows of some sort of in-depth guide on multiplier design I would be happy to read it. In fact, if someone would label the amount of voltage and amperage going through each component in the attached picture in terms of V0 (original voltage) and A0 (original amperage), that would be nice.
     
    Last edited: Feb 18, 2014
  4. ScottWang

    Moderator

    Aug 23, 2012
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  5. l0vot

    Thread Starter Member

    Apr 29, 2013
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    Thanks, That did help some. I still don't know how to calculate the amount of power the multiplier will provide for a given cap size, or how adding more capacitance to the lower stages will affect throughput (Wikipedia says it will help, but not how to determine how much it will help), or the diode load.It appears my components have a voltage rating capable of handling a power source with 5x the voltage of my current one, and will be getting closer to 22.6KV open circuit voltage. Also, I have given up on making a standalone multiplier because I would need waaaaay too many stages to pull that off.
     
    Last edited: Feb 18, 2014
  6. ScottWang

    Moderator

    Aug 23, 2012
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    Playing the high voltage power, you should calculate and try and modify the value.

    Electronic and Electric Circuit Simulation - capacitor online calculator.

    PowerLabs 200kV Voltage Multiplier!

    PowerLabs Twin Tesla Coils!

    Charge-Pump Voltage Doubler.

    If the rating voltage of diode is not enough, then you can in series with them.

    Do you have the high voltage probe? (maybe for 50KV)

    Have you ever consider about the isolation for the parts?
    Sometimes you can isolated with the plastic pad for table, the thickness should be over 1mm.
     
  7. l0vot

    Thread Starter Member

    Apr 29, 2013
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    In a previous post, I stated that my diodes and caps are probably rated for 5x the voltage they are required to be (I sort of picked components based off of the output voltage instead of the input voltage), so that isn't an issue ATM. As for isolation, I plan to stick each multiplier in it's own oil-filled PVC pipe to prevent arcing issues and increase the life of the parts. No, I don't have an HV probe. Currently I require information on power throughput based off of the caps in the multiplier, and diode loads so I can make sure I don't overload any of them.

    The multiplier is a two stage dual half-wave multiplier (which is an 8x full wave design) made of 15KV 100mA diodes which are rated for 200mA in oil, and 10nF 20KV caps. The power supply is a 2KV MOT. In the current design. How would I determine the amount of amperage available assuming the multiplier is not current limited by the MOT.
     
    Last edited: Feb 19, 2014
  8. ScottWang

    Moderator

    Aug 23, 2012
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    Do you want to attach the whole circuit, label the voltage and current, and including the MOT and how much current from it?
     
  9. l0vot

    Thread Starter Member

    Apr 29, 2013
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    I'm sort of thick sometimes, so attaching the whole circuit is probably the fastest way for me to understand it.

    Assume the device as it is described is under direct short conditions without any current limiting on the MOT* to see if the diodes can handle it. I don't know how much power I expect to get out of this setup, but I would like to know it's limits so I don't accidentally break it.

    *The MOT is probably capable of supplying somewhere .5A and 2A, but I have no way to check.
     
  10. ScottWang

    Moderator

    Aug 23, 2012
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    When voltage=2KV, Iout_dc= 500mAac/1.414 = 353.6mAdc
    Rate of Vin_ac transfer to Vout_dc = 11312V/2000V = 5.656
    500mAac/5.656=88.4mAdc
    So when the power output 11312V then the current only has 88.4mAdc
    For a high voltage over 10KV, the current has 88.4mAdc is a big current.

    The below has two kinds of DIY type for the High Voltage Probe.

    DIY High Voltage Probe for digital multimeters for 20KV.

    High Voltage Probe.
     
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