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Charger - Supply

Discussion in 'Electronic Basics' started by Randy Gross, Nov 3, 2004.

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  1. Randy Gross

    Randy Gross Guest

    Greetings,

    I am wondering if someone has or knows of anyone who has used a 12vdc
    charger as the foundation of a power supply? I have a 12v, 2 or 6 amp
    charger that I would like to use for this purpose.

    My Idea is to build a module that I could run the output from the
    charger into and vary the voltage and amperage from 0 - 12vdc and, 0 -
    6adc respectively. Simplicity is my goal, precision is a concern but
    not a priority. Can someone help me with the circuit?

    Randy
     
  2. Randy Gross

    Randy Gross Guest

    After some thought and a lot of math,

    I am looking at a new approach. Dividing the voltage would have been
    simple, if we put the power dissipated aside ( 72 watts ). The problem
    comes with stepping the voltage up incrementally. Each step in voltage
    would require a current division circuit ( dedicated ) to sustain the
    0 - 6A output in that range. Thats 12 circuits with resistors ranging
    from a few watts up to 60 watts, we're digging deep in the pockets
    now! Unrealistic!

    Instead, I've settled to keep the 12vdc constant and vary the current:
    | | | | |
    12vdc R1 R2 R3 R4 R5
    6A 12 ohm 6 ohm 4 ohm 3 ohm 2.4 ohm
    72W | | | | |
    <----------------------------------------

    Even still, the wattages range from 12 to 60 watts. I realize this is
    old school and inefficient but, simple.

    What I am trying to do is find the optimum DC control current for a
    Saturable Core Reactor I constructed. I tried 700ma at 6v from a cube
    and was encouraged by the response I got with less than an amp. My
    goal is to push the core to the saturation threshold to determine the
    maximun range of AC I can control with the reactor.

    Randy
     
  3. Randy Gross

    Randy Gross Guest

    OK! Back to the future.

    I think I've found a regulator that might fit the application. It is
    the LM338. There is only one concern I have with applying it to my
    purpose, the 6amp input. According to the LM338 datasheet, the
    regulator has an output range "in excess" of 5A but, I could'nt
    determine how much, sustained. The LM338 can handle surges up to 12A
    but I'm thinking this is momentary. Could I parallel two LM338s' to
    split the current and adjust them with one var. res. as in the
    following circuit:

    ----------
    | LM338 |
    ----|I O|------
    | | A | |
    | ---------- |
    | | | | | |
    12 vdc | | ---------- | | R R1 |
    | | | LM338 | | | R 120 |
    6A | ----|I O|------ R |
    | | A | | | +|
    CAP ---------- | | CAP
    .01mf |------- | 1mf
    | |-------------- |
    | | +| |
    | R2 R 5K CAP |
    | --R-> 10mf |
    | R | |
    | | | |
    --GND----------------------------------------------

    or, can I increase the value of the current set resistor ( R1 ) to
    lower the maximum current through the regulator.

    Randy
     
  4. I don't know whether parallel LM338s will work. It might work properly.

    However, here is a 5A adjustable voltage/current regulator that might
    work for you. Look on pg 16.

    http://cache.national.com/ds/LM/LM117.pdf

    --
    Regards,
    Robert Monsen

    "Your Highness, I have no need of this hypothesis."
    - Pierre Laplace (1749-1827), to Napoleon,
    on why his works on celestial mechanics make no mention of God.
     
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