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Discussion in 'Electrical Engineering' started by Rusty, Sep 16, 2004.

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  1. daestrom

    daestrom Guest

    We built a large 400 hertz power supply for subs back in 1960.
    It had to have a certain form factor to get it down through the hatch.

    Hi Bushbadee,

    Yes, that was one of the requirements of many pieces of submarine
    machinery!!! (even the main feed pumps :) I worked on several different
    400 hz sets, perhaps the oldest was 400HZ, 120V 3phase 42kW motor-generator
    sets used on the old Permit class (renamed after the Thresher accident in
    '63). IIRC, these were all mag-amp units. The only 'electronic' thing in
    them was the silicon rectifiers.

  2. bushbadee

    bushbadee Guest

    OUr converters were to replace motor generators.
    Lots of 2N174's
    the output was 120 volts, 3 phase.
    I wonder if there was any relationship.
  3. daestrom

    daestrom Guest

    I did also work on some smaller power 60hz to 400hz converters. IIRC, they
    had two 400hz inverters feeding a Scott-T for the 3 phase output. One
    'master' that fed main leg, and the 'slave' feeding the tee-leg. Phase A-B
    voltage controlled by master, phase B-C and C-A controlled by not only
    magnitude of 'slave' inverter, but phase shift delay from 'master'. But
    these were smaller units, only a couple of kW.

  4. Don Kelly

    Don Kelly Guest

    Don Kelly

    remove the urine to answer
    In this case there was probably a voltage regulator which acted to hold
    output voltage constant. In the case of a change in load, there would be a
    signal to raise the field current. With a high gain regulator and high field
    time constant, the use of a time derivative signal in addition to a
    proportional signal would be a benefit.
    In the original case the machine was a series machine so field current would
    be the same as the load current.
    Mag amps were hot items before SCR's came into use. They essentially served
    the same purpose and, at the time (1950's) were very useful for field
    control of generators -with faster response than previously available
    techniques for such purposes as excitation systems for alternators. In
    addition to a speed advantage there was also a saving in cost, physical
    size, complexity and maintenance. Another use was for dimming of theater
    lights. Simply a case where a technology came in that was better than
    what was there before and, in its turn, became obsolete for most
    applications when solid state devices became capable of handling the same
    currents and voltages.
  5. daestrom

    daestrom Guest

    (shudder!!!) I just had a flashback of re-brushing Amplidynes used for some
    old excitation systems ;-) Twice as many brushes as similar sized DC
    machinery. Considering the occasional failures I say of SCR systems, always
    thought mag-amps were the best.

  6. Don Kelly

    Don Kelly Guest

    At least the amplidyne had a reasonable response in comparison to the pilot
    exciter-exciter-field set up and used less space -with only one commutator.
  7. bushbadee

    bushbadee Guest

    We built them also.
    Did you by chance work for ElectroSolids or a competitor.?

    I worked on an interesting one.
    It was a pulse width modulated inverter. ac amplifier.
    An Input ac signal was amplified and rectified.
    That signal then acted as the reference for a pulse width modulated
    converter which chopped at double 40 Kc.
    The amplified half wave rectified signal was then fed to the center tap of a
    transformer which the then derectified the imput wave by haveing a pair of
    transistors which were tied to the input and detected 0 crossing of the
    input wave and kept the out put transistors in sync with the input.

    The thing was pretty flat to 4KC and down to about 20 cycles.

    The output had about 5% distortion.
    One of my ideas was to feedd the amplified signal to a class B or even a
    Class A amplifier as the DC input so the dc on the amplifer would track
    the output and achieve higher efficiencies than the theoretical efficiencies
    of class A and B amplifiers.

    I think Sony took out patents on the idea, but their patents were useless
    after I had presented papers on the theory and device we had built to the
    IEEE about 20 years before their patent.

    DR Middle brook also used the same idea to come up with a similer amplifer,
    but he used a bridge output and not a transformer which has quite a few
    I do not know if David ever built t he device, but we built, demonstrated
    and packaged our device and tried to market it as a high efficiency shake
    table driver.
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