Self exciting generator rotating rectifier diode polarity

Discussion in 'Power Electronics' started by jvcmarine, Mar 9, 2018.

  1. jvcmarine

    Thread Starter Member

    Mar 11, 2012
    Hi All,

    I have a 1988 18hp brushless self exciting generator.
    The rotor diodes have failed (open state).
    This rotor has four windings connected in series utilizing four diodes.

    After hours of research I am unable to come up with a diagram for this arrangement. Every thing I looked at used a three phase winding full wave with six diodes.

    I need to know the polarity orientation of the four diodes to re-install them onto the rotor windings.
    Additionally I was wondering what the voltage and current requirements for the diodes would be.
    I was thinking a Vishay VS series 16 amp 1200 Volt in a DO-4 (DO-203AA) case, similar in size to the old diodes.
    Can anyone explain how this ckt operates, current flow etc,,,,, Genny.png winding resize.jpg windings2 resize.jpg

    I have a diagram and pictures.

    Any help greatly appreciated.

    Thank You
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    All four diodes are mounted the same, so they will all be the correct polarity.

    The only problem is these Stud diodes can be Anode or Cathode threads, so can you see any markings on the diodes or do you know which polarity the stud ring is?
  3. jvcmarine

    Thread Starter Member

    Mar 11, 2012
    Hi Dodgydave,

    If you notice in the pictures you can see the rust encrusted diode, no legible markings whatsoever.

    The issue is, would you have:

    1-All 4 common cathode
    2-All 4 common anode
    3-2 common anode and 2 common cathode.

    The rectifiers need to be arranged so that the DC current sets up a North and South pole in the rotor. I just can't seem to understand how current flows in this ckt.
    I understand residual magnetism, bootstrapping, excitation stator coil, I just don't fully understand how the EMF from the excitation stator induced current AC into the rotor windings, and how the rectifier configuration is set up to control the current flow direction to create the north and south poles in the rotor. (Field).
    Maybe I'm just getting a little dense with age,,,