GMC Brushless Generator

Discussion in 'General Electronics Chat' started by debe, Feb 7, 2011.

  1. debe

    Thread Starter Well-Known Member

    Sep 21, 2010
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    Posted circuit of a GMC 950W brushless generator & wave forms under different loads on the 240V AC output. The waveforms are the rough bottom ones. Can any one explain how the capacitor & its windings actualy regulate the 240V AC output? FC is the Rotor & SC is the reactance winding.
     
    Last edited: Feb 7, 2011
  2. debe

    Thread Starter Well-Known Member

    Sep 21, 2010
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    Took a few measurements on the Genny. The one iwas using C is a10uf cap,With a 650W load C draws 1.5A & has 158V AC across it. With 500W loadC draws 1A & has 153V AC. With no load C draws .5 A & 125V ac. No cap in circ no output on genny. Change C to 18uf voltage across cap rises to175V AC & generator voltage rises to 270V AC. Still dont quite see how this all works.
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    <from other thread>

    Do you have a "mechanical schematic"/photo/etc, showing which windings are where when assembled?

    I see main coil, field coil, stator coil, but not quite sure what I'm looking at for the extra coil, or the one with the diode across it...

    --ETA: What are the top traces if the bottom trace is the output of the generator? What are the volts/div?
     
  4. debe

    Thread Starter Well-Known Member

    Sep 21, 2010
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    Hi thatoneguy. The top waveform is the local mains, the lower is the 240V output of the generator @ 50V/cm. Windings NC & SC & DC are all interwound as the stator. FC with the diode is the rotor. This is a brushles self regulating generator, very typical of cheeper generators.
     
  5. thatoneguy

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    I'm trying to guess what is causing the "steps" every 180 degrees in the output if that is all that is involved. :confused:
     
  6. debe

    Thread Starter Well-Known Member

    Sep 21, 2010
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    I was wondering if its distortion from the reactance & cap circuit as it changes shape at different loads.
     
  7. thatoneguy

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    The steps are in the same spot, phase wise (every 180 deg). At no load they have the inductive "spike" look, and at full load they are fully damped away.

    It's an odd setup, looks more like the output of an AC motor speed controller in use than a genset.
     
  8. debe

    Thread Starter Well-Known Member

    Sep 21, 2010
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    When the capacitor is removed there is no output on the generator, but the reactance winding has 6V ac on it. Iam only guessing here that the capacitor is drawing the current, & causing the reactance winding to induce more magnetism in the stator or the rotor?
     
  9. thatoneguy

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    Post some traces using slightly different valued capacitors (same voltage rating) with the same loads? Maybe double the value and halve the value to get an idea.

    For the loads, use light bulbs so there isn't any reactive power messing with the measurements.

    What year was this made? The steps remind me of a diac or neon bulb's breakdown in an odd sort of way.
     
  10. debe

    Thread Starter Well-Known Member

    Sep 21, 2010
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    Those wave forms were taken using lamps as a load. Next prob is having trouble, is taking photos of the CRO screen, parts of the wave form wont show up in the photos. The GMC generator was built in 2006, they are still coming out of China as 2stroke 850W generators under various brand names. The circuit is so dam simple. The stator only has the 240v windings, a reactance winding with the cap across it, & the 12v windings. The rotor only has 1 set of windings with a diode across the windings.
     
  11. thatoneguy

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    Is the diode a zener?

    I'll admit it, I'm confused. I can see the cap passing the power, but not regulating it in any way.

    If you an't get pictures, how much different does the waveform look with a larger or smaller cap? Amplitude difference, more/fewer spikes at which phase, etc?
     
  12. debe

    Thread Starter Well-Known Member

    Sep 21, 2010
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    Hi thatoneguy, The diode is just an ordinary power diode. About to post a series of CRO pics all 50V Cm div. This set are240v AC output at different loads. All loads are flood lamps. This is with the Cap changed to 18uf, which caused the o/p voltage to increase to 275V AC.
     
  13. debe

    Thread Starter Well-Known Member

    Sep 21, 2010
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    This set are taken across the capacitor & reactance winding. Cap is 18uf.
     
  14. debe

    Thread Starter Well-Known Member

    Sep 21, 2010
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    This set taken across Cap & reactance winding, Cap is 10uf as fitted to generator originaly.
     
  15. thatoneguy

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    How many channels do you have?

    I'm wondering if the extra smaller amplitude/higher frequency wave on the cap is at the same place the output has the diac looking "backsteps" in voltage. I'm thinking it must be.

    The output voltage is clearly controlled by the cap, though I'm not sure "regulated" is a word that could be used when referring to the output. Larger capacitor doesn't attenuate the low frequency as much, so it could probably be used as a 120VAC genset with a 6.6MFD cap.

    I don't think there's much of anything you can do to clean up the output other than a fairly large inductor for a low pass filter.
     
  16. debe

    Thread Starter Well-Known Member

    Sep 21, 2010
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    Heres dual trace of 240V ac & reactance winding overlayed 10uf cap & 50V/cm
     
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