Full wave voltage doubler question

Discussion in 'Power Electronics' started by Jazz2C, Aug 1, 2016.

  1. Jazz2C

    Thread Starter Member

    May 27, 2016
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    So my good friend and mentor @Hypatia's Protege is out of touch for the whole week so I can't reach her to ask about this circuit she suggested. Sry about the poor quality of the schematic!:( I have upload restrictions so I just cropped this from a pic in one of Hp's posts and (finally) got it uploaded to this thread (I hope).

    So plz consider just one of the doublers and see the signal source as an isolated LOPT secondary supplying a perfectly symmetrical 25 kvp sine wave. Also you can think of the link between the doublers as a hard ground. Ok, so my question is just that I'm wondering why Hp said it is greatly preferable to connect the outside lead from the LOPT to the left (diode side) and the inside lead to the right (capacitor side)? What difference can it make to an isolated winding?:rolleyes: What would happen if it was connected the other way around?:confused:

    Tnx for help and I want you all to know that Hp didn't assign this as a problem so I'm not cheating at homework!:)

    I'll try to link a pic of the transformer (from Hp's blog) below the schematic so plz keep your fingers crossed:cool:

    So here's the schematic
    Untitled.png

    Here's the transformer. The outside lead reaches from the top of the winding to the plate cap and the inside lead comes out of the winding and connects to the solder lug to the right of the winding.

    [​IMG]
     
    Last edited: Aug 1, 2016
  2. #12

    Expert

    Nov 30, 2010
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    The only thing I can see is a different capacitance to the core material, or a lower voltage breakdown capability to the core, but I can't say why that's important if the core is isolated by a large air gap from earth ground.
     
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  3. Aleph(0)

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    Mar 14, 2015
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    JC I can help you understand it but you have to work on your ideation skill which is solving problems by like walking through circuit operation in your head which I know you can do cuz you are good software debugger so this is similar skill:)!

    OK:)

    OK:)

    Which means it is at same potential as transformer frame (hint);)

    JC Even though HP didn't explicitly say that to me I totally agree with her:)!

    Now we're all set:D!

    So think on top divider all by itself so now:
    ⇒R(load) is connected between cathode of top diode and ground.
    ⇒Anode of bottom diode is directly grounded.
    So it's just 50kv FWD PSU with 10MΩ load.

    So you know you are on track here are statistics if we ignore effects of loading:
    ⇒Voltage across winding is 25kvp (which is totally within safety margin for winding's internal insulation:))
    ⇒Voltage across R(load) is 50kv DC

    Ok JC here's what you missed! Probably cuz of overthinking as usual:rolleyes:!
    ⇒Gnd referenced voltage at connection of C1 to C3 is 25kv DC (Sry about awkward wording cuz I wanted to avoid saying _junction_ to prevent confusion).
    ⇒Gnd referenced voltage at connection of diodes varies from 0v to 50kv (just think it through and you'll understand how it's 30khz, 25kvp sine wave with zero crossing shifted up to 25kv)

    So even though transformer is rebuilt for secondary to be insulated from frame, inside of winding to frame is still weakest point so it's best to just stress it to 25kv DC instead of pulsating 50kv! Also solder lug termination for inside lead is more subject to arcing and corona cuz of geometry and location.

    JC I want you to promise me you'll think on this until you identify block that left you confused cuz its like Plutarch said about illness and discord. You can't understand function without investigating dysfunction:)
     
  4. Aleph(0)

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    Mar 14, 2015
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    #12 You know what they say about assumption;) I surely do:oops:

    Anyhow I'm just too glad it wasn't a really tough question like the dreaded F vs FA filament lead mystery:eek::D
     
  5. #12

    Expert

    Nov 30, 2010
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    If I had assumed anything, I would have come to a conclusion based on that assumption. I did not assume. I did not come to a conclusion. I pointed out exactly the variable about which I made no assumption. I prefer that you not pretend to criticize me for being very careful not to make the mistake you named.
     
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  6. Jazz2C

    Thread Starter Member

    May 27, 2016
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    Got it! Tnx Aleph!:) I was feeling really dumb so against that frame of mind I'm relived to discover I was just lazy!:oops:
    So can we put my momentary lapse of cognition to good use by making sure any potentially confusing unqualified advice in the tutorial course is accompanied by rationale? I know it's lame but stumbling blocks like that can seriously interfere with the learning process b/c confidence is a big deal and ppl like me find it impossible to move on b4 totally comprehending previous lessons:oops:

    Yo #12 It's totally my fault b/c I forgot to mention that the transformer frame was at ground:oops: Anyway you said "if the core is isolated" so everyone knows there were no assumptions on your part. Also tnx for your point about winding to core capacitance b/c that could make a difference if the inside end was connected to the side of the network with a 25kvp signal component! Plz don't let Aleph's bossy big sis routine fool ya:D She even talks to HP that way and HP is her hereditary up-liner so to speak:D MAJOR TNX TO EVERYONE WHO TOOK TIME TO READ MY QUESTION!:)
     
  7. Jazz2C

    Thread Starter Member

    May 27, 2016
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    Oh yeah! You mean on RF heating magnetrons? FWIW I assumed (ooops!:p) that an emissive shield like a cathode sleeve or something of the sort was connected to the FA end?:confused: But anyway FA just means it should be connected to the anode of the HWD diode.:)
     
  8. Aleph(0)

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    Mar 14, 2015
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    @Jazz2C just for fun I got an ltspice simulation to run and the results are exactly what they should be:cool:! Now I'm happy too cuz I know I can upload files as long as they are png formatted:)!

    fwvd.png
     
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  9. Aleph(0)

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    Mar 14, 2015
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    #12 I'm sry you thought I was criticizing you:(! I just meant to be taking a jab at JC's penchant for ambiguity but my attempted humor went astray so please accept my apologies!
     
  10. Aleph(0)

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    Mar 14, 2015
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    You'll have to ask HP about that cuz she puts high value on rigor which means if you're comfortable then you're not working hard enough:rolleyes:
     
  11. #12

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    Too much rigor results in Rigor Mortis.
    And a dissertation sure to be undecipherable by most normal people.
    Probably only good for a reading in the House of Lords.:(
    Or do I give the House of Lords too much credit?

    In summary, I judge polysyllabic ultra precision at a disadvantage to readability.
     
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  12. Jazz2C

    Thread Starter Member

    May 27, 2016
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    Good one!:D

    For me prolix descriptions are best b/c I get stymied by unqualified assertions. I mean like the problem of my OP, it's just not good enough to say "do this" without a "why". Maybe the "whys" are obvious to more experienced ppl but it's like a concrete wall to electronics novices like me:oops: But if you really believe the ideas are drowning in verbiage that's a very important problem that Hp needs to hear about b/c she wants the courses to be universally accessible to English readers:)
     
  13. #12

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    Don't worry. I've told her more than once. Then I reverted to my belief that I can't make anybody change. It's up to her.
    Perhaps you could have a class of 30 grad students read her work and grade it for utility.
    Then you can kick yourself in the behind for wasting your time.:D
     
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  14. Jazz2C

    Thread Starter Member

    May 27, 2016
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    Tnx, Aleph!:)
     
  15. Jazz2C

    Thread Starter Member

    May 27, 2016
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    FWIW Hp has authored many well received technical papers on subjects related to another discipline so maybe her theory of interdisciplinary parallelism doesn't apply to electronics?:D When you think about it, electrical engineering is unique when compared to the hard physical sciences and science related trades in that emphasis upon creation of systems from total abstraction eclipses observation and speculation (like astronomy and particle physics) or repair (like medicine). Not that those fields don't require creativity but design of practically realizable systems from the realm of charge flow it totally phenomenal:) If I sound like an overzealous newbie it's b/c that's just what I am:cool:
     
  16. #12

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    Nov 30, 2010
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    That's OK with me.:)
    It seems that I have a disagreement with the style of HP. It is based on the idea that I can describe circuits and machine shop procedures with much shorter words, and I've been called, "very articulate" by a physician. Maybe her style is more, "normal" to people who speak, "British" and mine is more normal for people who speak, "American". If that's true, she is not wrong at all, but I find her style very difficult to read. It is precise, right after I use a dictionary on, sometimes as many as 3 words in a sentence. Im'a tell you, if it takes 5 minutes to read a sentence, I think something is wrong with the way the information is presented. HP might think something is wrong with my lack of vocabulary.:D It's a strong difference of opinion, and I don't think I'm going to win.:(

    If I cared to spend another thirty minutes on this, I could translate that paragraph into, "HP-ese" and you could take 10 minutes to read it, but I prefer my own style. I hope you find it concise.;)
     
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  17. Jazz2C

    Thread Starter Member

    May 27, 2016
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    Major Tnx to everybody! Sry I disappeared but Sturgis comes around only once per annum! No need to laugh! Hp and A0 think it's hilariously anti-intellectual of me to attend but my Sturgis is like @Hypatia's Protege 's Dayton and @Aleph(0) 's MIFF or EAA-AirVenture the last of which, by the way, involves plenty of greasy machinery too, Aleph!:p

    So honestly THANKS!:)
     
  18. crutschow

    Expert

    Mar 14, 2008
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    There can be a fine line between articulate communication and obfuscation.
     
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  19. Aleph(0)

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    Mar 14, 2015
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    JC if you drop an "n" from that then I'd say that's about right:p!

    Crutzschow that's right but unfortunately the line is different in the perception of every reader:(! So to help that HP is extensively using pictures to illustrate tasks cuz that's the universal language:)! We're also writing a glossary for discipline specific and trade jargon terms which also contains an expansion of every abbreviation used in text:cool:! And, I say most importantly, we're always responsive to questions and feedback:)!
     
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  20. Jazz2C

    Thread Starter Member

    May 27, 2016
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    That the best you can manage are plays on words proves I'm ok:p
    I know I'm the most partial reviewer of HP possible! Even so I find her precise, erudite delivery perfect and totally more intelligible than the dumbed down approach taken by so many web resources and hard bound engineering texts!:) I don't understand why English speakers object and sometimes resent eloquent use of their language and my first and only language IS American English!:confused:
     
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