Portable generator voltage regulator

Discussion in 'General Electronics Chat' started by tobe5052, Mar 23, 2009.

  1. tobe5052

    Thread Starter New Member

    Mar 23, 2009
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    ANyone have any ideas on how to regulate the output voltage on a ortable generator with brushes? Could a simple circuit be made to monitor the output voltage (or exciter circuit) and rectify that and then automatically adjust the current to the armature to stabilize the output voltage of the generator? This has to be rather basic to build rather than go and buy the expensive avr modules that come with the generators.
     
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Need more information, such as generator information, speed, existing controllers that perform the same task, etc.

    There are too many types of generators/alternators to even make a guess at a suggestion.
     
  3. tobe5052

    Thread Starter New Member

    Mar 23, 2009
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    Let me state what my issue is. I have a portable generator (Echo EG-4300) that works perfectly except for one issue. From a cold start, the generator outputs a voltage that can be adjusted by a pot on the avr to design voltage (manual says 252v at no load and design rpm of 3600). As the generator warms up the output slowly increases by a tenth of a volt steadily over time. I can bring the voltage back to 252v by the pot but it will again increase over time. If left alone the voltage will eventually increase to 280 then to 290, and over. I finally bottom out the pot and lose any further adjustment trying to bring the voltage into range. The generator has brushes. How are the reference voltages measured in the circuit? It looks like there is a coil in the stator feeding the avr (rectified and then being fed to the brushes?).
    The question is why is this happening?, and what can be done to correct the voltage shift. Can there be something added externally that will help with the presumed temperature compensation needed?
    Or is there something else I'm missing.
    One other thing. I obtained a second generator unit figuring I could use the avr out of that one. Both units exhibit the exact same results. I hesitate buying a replacement avr for some excessive cost and have no better results than I'm having now.
    Any thoughts would be appreciated.
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    Does the voltage increase under load?
     
  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    The AVR more than likely uses a 40:1 voltage divider, or some form of opto-isolator to sense the output voltage. Once output voltage is known, the uC varies the field current using PWM rather than the potentiometer constant current.

    What is the value of the pot? What voltage/current levels does the potentiometer control? e.g. Varies between 8 and 20V, or 10 and 15V at 2 Amps, etc.
     
  6. tobe5052

    Thread Starter New Member

    Mar 23, 2009
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    beenthere,
    Voltage does increase whether under load or not. The 120v output increased enough so a pellet stove control board ceased to function due to high voltage (during an ice storm loss of power, ....real handy).

    thatoneguy,
    The original pot was, if I remember correctly, a 10k cheap carbon pot (approx 270° swing in adjustment). The manual says initial setting is around 5k. I needed a setting of about 3700 ohms to settle in on the 252v no load output. I found that pot to be toooooo sensitive to be able to adjust so I changed it out to a 5k multi turn pot that really made the adjustment easy. I'll have to take some readings this weekend on min and max voltages for the extreme settings of that pot. But as i stated before, I eventually get the pot to one end and the voltage still rises. Were you saying the pot gets the voltage in the right range to begin with and then the uc takes over from there with PWM? Would you have a generic circuit as to how this would be constructed? I'll check the manual and see if there is a diagram of the connections to the avr so you know all that might be happening.
    Thanks for the input to date.
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
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    Electronically speaking, there are a lot of ways to skin that cat. The pot could simply set a reference level, or be somehow used as a control input. Very hard to say without a schematic, and those are usually not available these days.
     
  8. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    My post was only a guess. There already is a circuit adjusting the field current, otherwise the pot would have burnt from current.

    The question is what the pot controls - an input to a microcontroller, the bias on a transistor, etc.

    The more information that is provided, the closer an answer may be guessed at, but without a complete schematic, a solid working solution is very difficult, only experimentation, with the risk of destroying the generator or yourself.

    --ETA: If this is the similar controller you are referring to, it couldn't be designed/built for less than they are selling it for: http://www.generac.com/PublicPDFs/050120000S.pdf. 1-100A capability is a wide swing.
     
    Last edited: Mar 25, 2009
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