3 Phase AC Rectification

Discussion in 'General Electronics Chat' started by Slap, May 15, 2007.

  1. Slap

    Thread Starter New Member

    May 15, 2007
    3
    0
    Hi im currently converting a washing machine AC motor into a generator.
    I want to convert the AC output into DC. I know the basic schematic of this but dont know what size diodes to use.
    Also of interest would be what sort of load should i be using to test this circuit before the rectification. since its 3 phase output im not sure if i could do it on a basic multimeter setup.

    THe ac output should be 150v @5Amps from what ive read.

    any help on this would be greatly appreciated
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    The motor won't work as an alternator. See the article - http://www.allaboutcircuits.com/vol_2/chpt_13/7.html - which explains how induction motors work.

    An alternator works by rotating a magnetic field so the lines of force cut across the coil windings and induce currents. A permanent magnet DC motor can be used as a generator because it has the source of the magnetic lines of force built in. An alternator uses a current in the armature windings to make the magnetic field. There are slip rings and brushes on the shaft to pass this current into the armature. Your motor has no armature windings or slip rings to conduct current for the magnetic field - so it can't be made to generate electricity.
     
  3. Slap

    Thread Starter New Member

    May 15, 2007
    3
    0
    well thats what i thought.

    http://www.watchtv.net/~rburmeister/smart.html
    http://www.sustainability.ofm.uwa.edu.au/__data/page/83884/FP.pdf
    http://www.thebackshed.com/windmill/AssemblyA.asp

    but here are several pages showing that it can be, permanent motor AC motor without brushes that when rotated causes electricity generation. These all show it works just fine when used in a windmill without the startup voltage that alternators usually require.
    my question still stands if someone could help me on the diode size i would appreciate it.
     
  4. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    The motor described in the web pages is a permanent magnet motor. Is the 3-Phase motor you have also a permanent magnet motor or is it an induction motor?

    For choosing diodes, simply choose some who's current and voltage ratings exceed your expected need.
     
  5. Slap

    Thread Starter New Member

    May 15, 2007
    3
    0
    thanks. i wasnt sure if too high a diode would abosrob too much of the energy and add to the inefficiency of the generator.
    yeah i meant to write permament magnet motor not a permament motor motor :p
     
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