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Boost Electrical Engineering 3 phase converter, 1993

Discussion in 'Electronic Repair' started by N_Cook, Aug 17, 2012.

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  1. N_Cook

    N_Cook Guest

    Converting single phase to 3 phase to run a lathe from domestic supply.
    Hopefully just replacing the 415V 20A contact ratings 4 pole relay but I'd
    like to know a bit about how it works , in general terms, as both coil and
    power useage contacts are u/s.

    2 pairs of contacts paralleled to bring up to 40 amps rating. But I assume
    over time with bias to one set closing before the other one pair failed and
    then the second pair failed soon after but why the o/c coil , would there be
    a thermal fuse buried in the housing somewhere, lots of heat was developed
    from the bad contacts

    I assume the converter is peincipally an autotransformer to create the other
    phase in conjunction with some capacitance. There is a boost function that
    is manual biased switch at start of motor or automatic if the lathe cuts
    through a hard spot, this brings in more capacitance via the relay it seems.
    There is also a reed relay with a few turns of the power amperage passing
    around it , presumably the auto function ,but the mystery is a small TO3
    size bridge rectifier and electrolytic for a 100V or so DC supply for an
    offset or something
  2. N_Cook

    N_Cook Guest

    TO5 not TO3
  3. N_Cook

    N_Cook Guest

    this textually sounds the sort of thing

    "FIG. 1 is a 3-winding induction motor supplied from a single-phase power
    supply with a phase control consisting of a capacitor connected to a tap on
    an autotransformer."


    "The current in line L2 goes through a coil around a reed-relay so that the
    reed-relay contacts close when the current exceeds several times full load
    current, and the contacts open when the current is less than twice full load
    current. The coil is selected so that the contacts open when the motor shaft
    speed is greater than 80% of rated speed. The reed-relay contacts control a
    solid-state-switch which inserts the starting capacitor CS between terminals
    TC and T4. "

    not Solid State Seitch in this one
  4. N_Cook

    N_Cook Guest

    Sort of working order but will not drop out of boost mode. The voltage over
    the relay drops but not enough , it would seem , to make this replacement
    relay and so different coil demand, drop out. Will have to do some on site
    fudge adjustment to the original 6K8 dropper for this relay and check that
    strange bridge rectifier and offset DC function as no ac or dc without a
    load motor
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