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Constant Voltage Transformer for PSU

Discussion in 'Electronic Design' started by Richard, Sep 28, 2010.

  1. Richard

    Richard Guest

    I have a constant current transformer - along with capacitors and chokes
    and a PCB with electronics, from a Motorola or Schumacher battery
    charger (Motorala Type: 25E83071P03 or Schumacher 93-013-419). I think
    made in 1990. Outputted 14.25V or 13.8V depending on which outer taps on
    secondary was chosen.

    I've no idea what the electronics did on the PCB, but centre-tap (CT) of
    secondary is positive and the outer taps go to chassis via rectifiers.
    CT goes to a capacitor of 97,000 uF, and then a choke, then another
    capacitor of 73,000 uF.

    Wires (probably "signal" voltages) from both of the outer taps of
    secondary goes to the PCB.

    The tank circuit has the capacitor. But both ends of the capacitor go to
    the PCB - one of the wires via an iron-cored choke (not some small RF
    choke).

    Okay, the question is, can a basic PSU be made with the following items
    only?:

    * CVT

    * both rectifiers

    * both "smoothing" capacitors

    * smoothing choke

    * capacitor for tank winding

    All the rest not used.

    Thanks.
     
  2. Rich Grise

    Rich Grise Guest

    Yeah, but the only regulation you'll get is what the CVT regulates
    to. (or whatever you slap onto the output) What you've just described
    is the bog-standard introductory basic DC power supply. :)

    Now, if this CVT is actually something like a mag amp, then, of course,
    all bets are off. ;-)

    Have Fun!
    Rich
     
  3. Richard

    Richard Guest


    Basically I would have ended up with something similar to:

    http://www.circuitstoday.com/wp-content/uploads/2009/10/CVT-Power-Supply.jpg

    I had parts for a more sophisticated circuit arrangement where the
    voltage across the AC capacitor was fed to a PCB, via a (rather large)choke.

    Anyway, on leaving out the connections to the PCB, I'm sure I would have
    got a working PSU similar to the circuit in the link.

    But, I've decided to take all the windings off the core, I've removed
    the magnetic breaks, and I'll rewind for a conventional transformer.

    So, my project has completely changed! It's now about winding a
    transformer.:c)
     
  4. GregS

    GregS Guest

    I remember the supplies they used to use on the early DEC computer
    systems. Just a CVT, rectifier, and "computer grade caps".

    greg
     
  5. Rich Grise

    Rich Grise Guest

    Not to worry too much; it will work as a conventional transformer, the
    iron is the same, it's just terribly stupid and wasteful to tear apart
    an already working ferro-resonant transformer. The guy probably won't
    burn the house down, but he's shot himself in the foot by degrading
    a working ferro CVT to a linear.

    I used to work for a guy who designed ferroresonant transformers. The
    "official" name for those "magnetic breaks" is "shunt(s)"

    Take them, and the resonant winding away, and it's no different from any
    other silicon steel transformer core, except for the HUGE winding windows.

    One time, he designed a new ferro xfmr, and I was at the bench testing
    it - there was a mongo variac with a knob about the size of a steering
    wheel, and big AC voltmeters and ammeters.

    So, I plopped this brand new ferro transformer on the bench, start
    cranking up the variac, and at about 3 VAC on the primary, it was drawing
    about seven amps! I freaked, looked at the boss (the guy with the black
    magick knowledge of how to design one of those beasts), and he was
    beaming: "It's regulating!"

    The primary makes more flux than is needed; the shunts let that flux
    slosh around the core, which might or might not saturate on the peaks -
    the resonant winding makes saturation pretty much irrelevant, because
    the magickal confabulation of the magnetic shunts and the resonant circuit
    (they use big can capacitors for what he called "the ferro winding")
    result in a pretty much constant-voltage output.

    I agree, it's kind of stupid to dismantle a working ferroresonant
    constant-voltage transformer; but the worst that will happen is:
    1. If you don't use enough turns in the primary, it will burn out,
    same as any other iron core coil across the mains;
    2. All you'll have is a plain ol' ordinary linear transformer, with
    all their attributes, so to speak.

    The reason not to tear it apart isn't danger, it's why screw up something
    that's already working as advertised? And he could very easily have
    changed the number of turns on the secondary to get any output he wanted.

    Cheers!
    Rich
     
  6. Richard

    Richard Guest


    I thought if it was not drawing it's load current, it was going to be
    wasting power. I know they run hot. So, I thought, make it a regular
    liner transformer.

    It could be put back again, in theory, but I'll just dabble and
    hopefully make a nice regular linear transformer. Rich
     
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