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  • #16
    <font face="Verdana, Arial" size="2">Originally posted by J Tiers:
    Actually, it works.

    The key is, as usual, buildup.

    In the case of a DC generator, residual magnetism is needed to induce some field current, which then creates a larger field. It is a positive feedback system that ends up at full voltage.

    In the induction AC generator, a small residual field induces rotor currents, which then create stator current, and it will build up if the load is right.
    The usual system apparently is to load it with capacitors to draw current for buildup, otherwise unloaded, and then connect the load.

    I actually tried it, and got output from the induction motor. I had to "zap" it with a small battery to get some residual in the stator iron before starting it up.

    </font>
    Yes J you are right it does work.The example I saw was a 10hp single phase 3600 rpm coupled to a 1800 rpm three phase motor.The way it worked the unit was started up and one coil of the three phase motor was flashed with DC to the tune of 180v.The instant it was flashed the generator began producing three phase output.However it did have a stall point,once the unit was loaded beyond it's limit(slippage?)it would quit generating and have to be flashed again to restart.

    The old guy who had it had a brick company setup out in the woods near here and it ran his pug and ball mills,when he died the business went with it.

    For my two cents I wouldn't bother,the home brew converters work good enough.The two 20hp units I put together are working flawlessly since four years ago,that and I figure if one of those will start a 15hp,then a 7-1/2 and finally a 5hp that's good enough for me.

    I just need one more tool,just one!

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    • #17
      Flashing a winding, or relying on residual magnetism to start you off, doesn't control your phases reliably. The motor/generator will start generating 3-phase something, to be sure, but what? If your phases happen to start backwards (maybe "clockwise" vs. "counterclockwise" is the way to think of it), motors you try to run off the resulting current will run either forwards or backwards when switched to "forward".

      Automotive generators (back when there were such things) could rely on residual magnetism to start them going, and so could start without battery current. When converting a car between positive and negative ground electrics, the generator could be flashed manually with momentary battery contact to supply the correct polarity of residual magnetism.

      But in that application there was no uncertainty in polarity (or, naturally, phase).

      Comment


      • #18
        Using induction motors as generators works just fine and is efficient too. A friend and customer of mine generates 120 kilowatts of power from a small river and sells it to the power company. He uses pumps as turbines and motors as generators.

        http://www.smallhydropower.com/more.html
        Free software for calculating bolt circles and similar: Click Here

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        • #19
          <font face="Verdana, Arial" size="2">Originally posted by sauer38h:
          Flashing a winding, or relying on residual magnetism to start you off, doesn't control your phases reliably. The motor/generator will start generating 3-phase something, to be sure, but what? If your phases happen to start backwards (maybe "clockwise" vs. "counterclockwise" is the way to think of it), motors you try to run off the resulting current will run either forwards or backwards when switched to "forward".
          </font>
          Most applications I have seen for this were out in the boonies hydro etc setups. Mostly for lighting, and often multi single-phase instead of three phase loads. Clearly no problem there.

          But, I don't think that your statement is correct.

          Since the rotation of the input shaft is consistent, I think the phasing will be consistent also. It's AC, after all, and whether it starts out negative or positive going is immaterial.

          The key is how the sequence is. The motor is "reversible" in the energy sense. You are putting in electric energy to get rotational in a specific direction, OR rotating it in a specific direction to get electrical energy out. As a motor, it generates a back EMF.

          The rotational input =&gt; electrical energy is essentially using the back EMF as its output, using the capacitive loads as the exiting source. The back EMF is of known *polarity* or sequencing dependent on rotation. So the output as a generator should likewise have a known and predictable sequencing depending only on wiring and rotation of the input shaft.
          1601

          Keep eye on ball.
          Hashim Khan

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          • #20
            This might be of interest.

            http://www.shockfamily.net/triplehex/index.html
            Dan

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            • #21
              Interestingly, the single-phase motor thing isn't patented.... not by Otto J.M. Smith, anyhow.

              One presumes that one of the 3phase motor static converter patents is what they are referring to, although in my skim of the sensationalist info they seemed to indicate a single phase motor...... Probably its 3phase connected to single phase.

              In any case, he has patented the rotary converter, the static converter, and about 2 dozen other things, including three or 4 other 3phase motor items.

              I've no idea how well they work, but I presume a pump is ideal, as it has such a constant load. It can be tuned to a degree that a variable loaded motor cannot......
              1601

              Keep eye on ball.
              Hashim Khan

              Comment


              • #22
                Hey, I think I'm actually starting to understand some of this Greek.

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                • #23
                  <font face="Verdana, Arial" size="2">Originally posted by Dangf:
                  This might be of interest.

                  http://www.shockfamily.net/triplehex/index.html
                  Dan
                  </font>

                  What? He doesn't have a 3,000 mpg carburettor, too?

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                  • #24
                    Naw, I'll bet that for certain restricted applications, the efficiency CAN be higher. The pump has such a constant load that it could be tuned..... a fan likewise. But a general purpose motor I don't think can be set to any and all applications with one set of caps etc..... I'll have to read the patents someday, its required to be fully disclosed in them.

                    Of course, equal attention to a 3phase motor on 3phase would improve it too......

                    I presume he is tuning it for best power factor, etc, but I haven't followed up the patents, I have other things to do.

                    Much the same problem seemed to crop up when I looked at RPCs. The load affected the best value for the balance caps.

                    [This message has been edited by J Tiers (edited 01-03-2006).]
                    1601

                    Keep eye on ball.
                    Hashim Khan

                    Comment


                    • #25
                      The written pole principal-

                      http://www.precisepwr.com/Technology.asp?bhcp=1
                      I just need one more tool,just one!

                      Comment

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