Onan 3 Phase Gen Set

Discussion in 'Shop Talk' started by vicker, May 29, 2006.

  1. vicker

    vicker Well-Known Member

    Jul 11, 2003
    Central S. C.
    I got a good deal on a used Onan Gen Set. 6.5 kw 3 phase for $350. We replaced the 220 plug with two seperate 110 oulets and it works just great.
    It is my understanding, that I can step the 3 phase down with transformer and get more 110. What type of trasformer am I looking for? Would Grainger have it?
    Thanks again :D
  2. tyusclan

    tyusclan Well-Known Member

    Jan 1, 2005
    Was your 240 plug a 4-wire or 3-wire? If it was only a 3-wire and you seperate it into 2 120 volt plugs, then you don't have a neutral on your outlets. Your getting 120 volts across the ground, which can be very dangerous. If it's 4-wire, then you're fine, because they have a neutral and a ground.

    Your 3-phase probably only has 3 hot wires and a ground. If so, then you're not going to be able to split it into 120 volt outlets, again because you won't have a neutral. If you do have a neutral you can check across each terminal and the neutral, one at a time, to make sure they all have equal voltage. If they are all equal, and you have a neutral available, you can hook an outlet to each terminal. If you have one leg that has 240 volts on it alone across a neutral, then you have a stinger leg, and you CANNOT use that as a 120 volt outlet. There is nothing to "step down" because the voltage is already 240 volts. You can either pick any two with a ground for 240 single phase, or as I described above for 120 volts.

  3. John Hill

    John Hill Grand Master

    May 12, 2002
    New Zealand
    It is not a simple matter to answer your question as the 3 phase alternator may be built and connected in a variety of ways. There are two key words applicable here 'star' and 'delta'. Do either of these words appear any where in the description (manual?) or on any name plates etc? There are symbols for these too, a triangle and a three legged symbol (like the centre of the Mercedes grillbadge). The three legged symbol might have a fourth wire comeing from the centre.
  4. farminghandyman

    farminghandyman Well-Known Member Supporter

    Mar 4, 2005
    get a hold of a manual before you burn the thing up,

    if it is a 12 wire unit you can have the out put rewired to most any type of configuration you could dream of, for three or single phase out puts,

    I have a three phase 12 wire generator and you can even wire it for just 120 volt single phase if that is your desire, I had mine wired for 120/240 single phase, for years untill I put in 240 wild leg delta three phase, and now have it wired for the three phase,

    but it would be best to rewire the output, it to balance the load on the windings and the generator, and make sure that your not hurting the windings and the power you producing is what you need,