Strange voltage drop on CRC filter.

Discussion in 'General Electronics Chat' started by coinmaster, Jan 9, 2016.

  1. coinmaster

    Thread Starter Member

    Dec 24, 2015
    350
    6
    Hi, I just built a CRC filter for a bipolar power supply and I'm getting a voltage drop I do not understand.
    http://postimg.org/image/d9yi9kcbf

    I should be getting like +/- 300v after the rectifier but I'm only getting around 170v.
    I've confirmed the AC before the rectifier is 240v.
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,163
    1,796
    No image there. Please include the image in your post.
     
  3. coinmaster

    Thread Starter Member

    Dec 24, 2015
    350
    6
    Last edited by a moderator: Jan 10, 2016
  4. Papabravo

    Expert

    Feb 24, 2006
    10,163
    1,796
    Why do I get an advertisment that I can skip and what is up with needing Flash Player. If you want people to help you with your problem you absolutely have to stop throwing up obstacles to us doing that. Just include the image in your post. Is that explicit enough for you or do I need to use a 2x4 to get your attention?
     
    Last edited by a moderator: Jan 10, 2016
  5. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    You should be getting 336 volts across your output points. Your ground is meaningless and is basically floating.

    Your second photo link works for me.
     
  6. Veracohr

    Well-Known Member

    Jan 3, 2011
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    76
    I can see it just fine Papabravo, and I don't have Flash.

    Coinmaster, do you mean you're seeing +170V and -170V (340V between the two), or only 170V across the two?
     
  7. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,648
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    Could you post the circuit?
     
  8. coinmaster

    Thread Starter Member

    Dec 24, 2015
    350
    6
    170v across the two. The voltage taken directly from the rectifier output is +/-170v. and exits the filter as +/- 170v.
     
  9. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Since there is a GND symbol on your schematic, your statement about +/-300 V is incorrect. You will get approx +/-170 V. 240 x sqrt2 = 340. With a centerpoint voltage divider, that's +/-170.

    However, capacitors make horrible voltage dividers, primarily because large electrolytics can have tolerance specs of -20%/+80% or worse. So while the outside terminals probably will measure 340 V, the centerpoint will wander around with temperature, load, the phase of the moon, etc.

    ak
     
  10. coinmaster

    Thread Starter Member

    Dec 24, 2015
    350
    6
    Ah, so in order to get +/-340v I would need double the AC voltage, I'm guessing the waveform is split in half giving half the rms voltage of the AC, I have much to learn it seems.
     
  11. Lestraveled

    Well-Known Member

    May 19, 2014
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    Yes. Connect one of your AC inputs to your ground and you will get +336V and -336V around ground.
     
  12. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Expanding on that - There will be twice the voltage, but there also will be at least twice the peal-to-peak ripple voltage. No free lunch.

    ak
     
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