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Discussion in 'Electronic Basics' started by Jim, Nov 7, 2004.

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  1. Jim

    Jim Guest

    Hi,

    I would like to make a 800V DC power supply, which will be used to charge a
    capacitor bank. The power supply will run of a 12V battery. To make the
    power supply I am thinking of making an oscillator, which will generate a
    12V AC signal. The 12V AC signal will then be fed to a transformer, which
    will step the 12V AC signal upto 800V. I will then use diodes to convert
    the 800V AC signal to approx. 800V DC.

    I would like to make my own transformer (I can't find any suitable premade
    transformers). I understand that the transformer will need a ratio of
    800/12. But how do I determine how many turns I should have on the primary
    coil? Also, how do I determine the best frequency for the transformer?
    Should the frequency be as high as possible? And what about wire thickness,
    how thick should it be? Do any calculators exist which will tell me all
    this?

    Can anyone point me in the right direction (websites or answers)?

    Thanks.
     
  2. Do you have an idea of the current you will expect (or how big a
    capacitor you need to charge in how much time)?

    Do you need isolation between the 12 volt source and the 800 volt DC
    output?

    I suspect that a flyback converter may be good for this sort of thing,
    since it handles big voltage variations in the output (like starting
    with a fully discharged capacitor load that ramps from zero to 800
    volts).

    This type also reduces the turns ratio required, because it can
    produce more than 12 volts across the primary.

    An old TV or monitor flyback transformer (and built in high voltage
    rectifier) might serve.
     
  3. Jim

    Jim Guest

     
  4. Jim

    Jim Guest

    Sorry, I accidently hit the send button on my last message.

    I don't really know what the current requirements are. The capacitor bank
    is around 800V @ 700uF. The time it takes to charge is not really an issue.
    If it takes a while then that is fine.

    I do own a flyback transformer (from a computer monitor), but I would rather
    make my own transformer (more fun and I would learn more).

    I guess it would be better to make a transformer which can generate 200V and
    then use a voltage quadruppler (diodes and caps). Hopefully the voltage
    quadruppler would give me 800V.

    I don't know how many turns to use or which wire gauge to use. The best
    frequency to use is a bit of a mystery as well. Surely some formulas (or
    simulators) exist, which will allow me to work out what I need. How do
    people normally go about working these things out?
     
  5. First they learn about the circuit configurations available and pick
    one or two good candidates. (I mentioned the need for an ability to
    handle loads that vary from nearly zero volts to 800 volts as an
    example.) Then they study the design of the magnetic components
    needed.

    I suggest you study the flyback converter (or boost regulator) from
    several sources, till you have a basic understanding of the concepts.
    You might start with this reference on switching converters:
    http://www.national.com/appinfo/power/files/f5.pdf

    When this study has allowed you to have a specification for the
    inductive components (inductance, current levels, magnetic energy
    storage capability, etc.) you need to read up on the design of the
    magnetics, themselves. Many core manufacturers have tutorials at
    their web sites. Lots of the design formulas are in the back of the
    catalog (page 163) from Fair-Rite:
    http://www.fair-rite.com/fr_catalog-14thed_rev3.pdf
    but you may need a lot more hand holding than this brief reference to
    understand all the design process.
     
  6. peterken

    peterken Guest

    one of the nice things of resonant circuits using transformers is that they
    can go pretty high on the secondary side.
    try using your transformer in an oscillator circuit, OR

    another way is using a 12V to 220V transformer (standard 220V to 12V but
    using it reversed), and use a simple tripler-circuit to "amplify" the
    secondary side.
    regulating the 12V side voltage will regulate the 800V side then

    tripler schematic (view using notepad and fixed font)
    extending the tripler can be done by adding more of the same on the dots
    (gives higher voltage then)
    enlarging capacitors allows more current
    choose a frequency for the 12V side giving you some "resonant upswing" in
    the transformer (but don't overdo it or it breaks down...)
    12V ac in and doubling the secondary side gets you about 600V already, so be
    carefull please !

    o--||--+------+--||--+.....--o V+
    | | |
    --- --- ---
    ac in / \ \ / / \
    --- --- ---
    | | |
    0------+--||--+------+.....--o V-





    Hi,

    I would like to make a 800V DC power supply, which will be used to charge a
    capacitor bank. The power supply will run of a 12V battery. To make the
    power supply I am thinking of making an oscillator, which will generate a
    12V AC signal. The 12V AC signal will then be fed to a transformer, which
    will step the 12V AC signal upto 800V. I will then use diodes to convert
    the 800V AC signal to approx. 800V DC.

    I would like to make my own transformer (I can't find any suitable premade
    transformers). I understand that the transformer will need a ratio of
    800/12. But how do I determine how many turns I should have on the primary
    coil? Also, how do I determine the best frequency for the transformer?
    Should the frequency be as high as possible? And what about wire thickness,
    how thick should it be? Do any calculators exist which will tell me all
    this?

    Can anyone point me in the right direction (websites or answers)?

    Thanks.
     
  7. Steve Evans

    Steve Evans Guest

    Yes, you need a copy of a book called the 'Coil Design and
    Construction Manual', published by Babani Press in Britain for just 4
    pounds Sterling. The chapter on power transformers in conjunction with
    the tables in the back cover *everything* (and I mean everything -
    former, core type, turns, turns ratio, wire size, winding spacing; you
    name it!) you need to know. You should be able to get this excellent
    book even cheaper on e-bay. Good luck!
     

  8. Greetings Jim.

    You ask all very good questions. The answers to your questions however can
    be quite lengthy. There are entire books dedicated to answering just some
    of your questions.

    That said, I highly recommend reading (and/or watching the narrated slides)
    of the Magnetics Design Handbook that Texas Instruments is generous enough
    to provide to the world for free. You can get the goods here:

    http://focus.ti.com/docs/training/catalog/events/event.jhtml?sku=SEM401014

    If you are serious about fully learning the answers to your questions, you
    will want to download, save, and eventually read the whole handbook in the
    slup222.zip file which can be downloaded from the above link. Although the
    handbook is pretty comprehensive and contains most of the answers to your
    questions, you will likely need to read it more than once while
    simultaneously supplementing that reading with other books (perhaps from
    your local university's science library) and personal experimentation before
    fully understanding the answers to your questions.

    Good luck Mr. Jim.
     
  9. Active8

    Active8 Guest

    On Mon, 08 Nov 2004 19:16:08 -0500, John Popelish wrote:

    What, you no lika http://genome.dna.tripod.com/ ?

    Actually, that nat'l doc looks ok.
    And free design/selector tools. Same for the controller chips -
    Nat'l, TI, Maxim, LTI ... LTI - friggin' amazing company. A new
    controller every month in EDN or wtf mag it is.
     
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