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Winding a conventional AC line frequency transformer

Discussion in 'Electronic Design' started by Eeyore, May 13, 2007.

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  1. We have done something similar to that on our test sets to minimize
    transients when switching to different voltage taps. We use an SCR
    controller set to phase fire initially at about 70 degrees to minimize "DC
    offset", which occurs when an inductive load is energized. We add a power
    resistor in series with the capacitor to create a snubber. Otherwise the
    instantaneous application of voltage to the capacitor draws a high current.

    There is also the effect of remanent magnetism, which causes a high inrush
    current when voltage is applied. I believe the high inrush occurs if the
    phase of the applied voltage matches the phase at which the voltage was
    previously removed. The core is already magnetized in that direction, and
    saturation occurs very quickly. A gradual soft-start with phase modulation
    can minimize this.

    I have used some large thermistors from, but they get
    quite hot, use up extra power, and must cool off before becoming effective

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