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Good way to test variable-speed generator output?

  1. Nov 19, 2009 #1
    I need to test a variable-speed generator attached to a small wind turbine (lets say). I want to see how much power its producing, as well as the current. It outputs in three-phase Y configuration at frequencies varying from 3 to 9 Hz. The generator is rated at 1.2 kW at 550RPM, with an open circuit rectified DC voltage of 380 V.

    I have zero experience working with high-power motors and generators and how to test them. I think the best bet would be to use a purely resistive load, correct? I'd have to use some robust resistors - my thinking was to setup a "bank" of resistors in parallel to meet the power requirement and then connect one bank to each phase. I could then measure voltage, and knowing the resistance of the bank determine power for each phase, right?

    Would the load resistance matter in determining output power? Does the load effect how hard the generator is to turn, etc?
  2. jcsd
  3. Nov 19, 2009 #2
    I think you are actually talking about a dynamo, meaning a brushless alternator with a permanent magnet rotor. The best way to test this is to use the rectified dc diode output (2 per phase) into a single resistive load. You can use a voltmeter to diagnose individual phases. To completely test this you will need a variable speed motor capable of ~1.5 HP at 550 RPM (torque = 26 Nm). Using a fixed-1740 RPM induction motor is not suitable. Electric drills could provide the correct RPM, but lack the torque (HP). The load resistance value depends on the no-load dc output voltage (which is linearly proportional to RPM), and the magnetic coupling efficiency between the magnets and the pickup coils.
    Bob S
    Last edited: Nov 19, 2009
  4. Nov 19, 2009 #3
    Hmm, I don't think it's a dynamo... it outputs three phase power. Here is the website:

    www.Ginlong.com [Broken]

    I know that I need a voltmeter, but we would need some type of load to deliver the power to, right? I could find open circuit voltage just by spinning it, but I want to see the power delivered through an actual load... I think.

    Thanks for the help.
    Last edited by a moderator: May 4, 2017
  5. Nov 19, 2009 #4
    They call it an alternator, but it does not have a slipring to contol the output voltage. Perhaps a PM generator is a better name.

    I agree. If it is a commercial PM generator, its output impedance should be fairly low, but still you need a plot of voltage vs. RPM before you can buy or make kilowatt resistors.

    [added] The GL-PMG-1000 PM generator will put out 1600 W and 350 volts at 550 RPM. Nice generator. The resistance should be R = V2/1600 = 76 ohms #@ 1600 watts. You could parallel about 13 1000-ohm 100-watt resistors for full load measurements.

    Bob S
    Last edited: Nov 19, 2009
  6. Nov 19, 2009 #5
    Ginlong provides power and voltage curves for the model, but I'm looking to test/confirm it and do some additional testing in the future.

    http://www.ginlong.com/images/200906/1000-PMG-Power-Curve-1.jpg [Broken]

    http://www.ginlong.com/images/200906/1000-Open-Circuit-Voltage-1.jpg [Broken]

    Couldn't I just make a bank of say 100 resistors in parallel so I don't have to have resistors rated at 20 W each, etc?
    Last edited by a moderator: May 4, 2017
  7. Nov 19, 2009 #6


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    Last edited by a moderator: May 4, 2017
  8. Nov 19, 2009 #7
    You could cannibalize toasters, hairdryers or other used appliances for some nichrome resistance wire instead of buying a bunch of power resistors. You can stretch out segments for testing various loads.
    Last edited by a moderator: May 4, 2017
  9. Jul 13, 2011 #8
    I have a question. We have a 480V, 3 phase,1500.KW emergency generator in my hospital.What is the maximum load can we connect it? most of our loads are motors and pumps. I heard we can connect only 1/3 of the capacity of the generator because the motors are taking starting 3 times current. That means onlky 500KW.Is that true?
    Other thing is that most of our motor starting with VFD. Is there any difference of starting current if motor starting with VFDs.

    How do we calculate the load when it is running. When our last test we got the amps readings 826,820 and 796 respectively in each phase. I know the power is 1.73x volt x current x power factor.what will be the amps and volts for calculating?The line voltage was showing 282 in each phase.

    The way my co wokers are calculating is 1.73 times total amps(2442) times 282Volts/1000 to get the KVA.Is that aright calculation?
    I hope some one can help me.
  10. Jul 22, 2012 #9
    Performing an Open circuit test and a Short circuit test can help you.
    You will be needing a voltmeter and an ammeter.
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