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Home made generator?

Discussion in 'Electrical Engineering' started by, Mar 12, 2009.

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  1. Hi

    I don't know as much as i'd like about electrics, but i thought someone here
    might be able to help.

    Here's the thing...I need a generator. New, they're around £100 for a 750W,
    but I've got an old 3.5 bhp engine which, i imagine is half of what the
    generator actually is.

    What i'd like to know is there anything i can buy (like just the generator
    bit) or use (like a car's alternator) to 'bolt on' to the engine to produce
    electricity to power lighting/power tools save buying a new genny?

    Any thoughts appreciated!
  2. John

    John Guest

    "" wrote
    It will probably cost you more in materials and parts than it would to buy a
    new unit.

    It will certainly cost you vastly more in terms of your time and effort
  3. The Lucus alternator used in old UK minis (and some other UK cars of
    that era) generated up to 42A at idle speed, but only went up to about
    48A max a little above idle, and produced no further increase in power
    output as you raised the engine speed further. Nowadays, alternators
    are controlled digitally by the engine management unit, and won't work

  4. No... Roy... You cannot.
  5. James Sweet

    James Sweet Guest

    Big alternators are everywhere these days. The factory Bosch unit in my
    Volvo 740 is 100A and it has a convenient internal regulator. I have an
    extra one in the garage awaiting just such a project, since I also have
    a perfectly good 3HP engine sitting around. Any luxury car from the mid
    80s on should have at least a 70A alternator. Seat heaters, power
    windows, power seats, all that stuff sucks a lot of juice.
  6. James Sweet

    James Sweet Guest

    If you run the field coil flat out, you can get even more than that
    without rewinding. You have to spin it pretty fast and obviously you
    will not get anywhere near the full rated load current. The output is
    unfiltered DC unless you tap off prior to the diode pack in which case
    it will be 3 phase AC.
  7. James Sweet

    James Sweet Guest

    Clearly if you were to go buy all the parts it would, however he has an
    engine already, and a used alternator can be had for anywhere from free
    to $30 bucks or so, can't really factor in the time and effort if you're
    the sort who enjoys this stuff, and what decent engineer doesn't?
  8. Many thanks for all the replies, folks. You've all given me something to
    think about.

    And now I think I'm going to try and get hold of a decent sized alternator
    and give that a go.

    Cheers again!
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