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Gen set voltage problem

Discussion in 'Technical Discussion' started by G650driver, Apr 15, 2015.

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  1. G650driver, Apr 15, 2015
    #1
    G650driver

    G650driver New Member

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    . I'm having trouble with voltage fluctuations on my Onan 7.5 generator. The RPM's seam stable but I'm getting some 10 volt swings occasionally but more often it just flutters a couple of volts with accompanying light flickering etc. I suspect it has caused the failure of one refrigerator. A new voltage regulator ain't cheap so I was hoping for some other ideas. I've tried adjusting the dampener screw on the board. I seems to help some but I can't seem to cure it completely. Any tricks to this that might help?
  2. G650driver, Apr 15, 2015
    #2
    G650driver

    G650driver New Member

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    Ps, it's a 1976 Bertram 42.
  3. K1W1, Apr 16, 2015
    #3
    K1W1

    K1W1 Senior Member

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    Does the frequency fluctuate at the same time?
  4. G650driver, Apr 16, 2015
    #4
    G650driver

    G650driver New Member

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    Well, you got me on that one. How can I tell? I've got a volt meter and an amp meter. Are you talking 50 vs 60 hz? Greek to me. Sorry, but that's over my head. I did spend some time chasing some ground wires and found some coroded terminals on a battery. I cleaned that up and it seemed to help. Could a dirty battery terminal cause this?
  5. G650driver, Apr 16, 2015
    #5
    G650driver

    G650driver New Member

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    The frequency of the lights flashing?
  6. K1W1, Apr 16, 2015
    #6
    K1W1

    K1W1 Senior Member

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    I am guessing your Genset is 60hz. If the frequency fluctuates this might indicate a speed change. A voltage change at constant speed could be an issue with the exciter circuitry
  7. Pascal, Apr 16, 2015
    #7
    Pascal

    Pascal Senior Member

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    RPM directly affects frequency, not voltage so it's. Important to check frequency. Most quality multimeters can measure

    When does th voltage flucTuation happen? Is it when a load kicks in like a big air con compressor or random?
  8. K1W1, Apr 16, 2015
    #8
    K1W1

    K1W1 Senior Member

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    RPM has an effect on Voltage that is why when a heavy load is suddenly applied the voltage will drop till the engine catches up and when a sudden load drop will cause an increase in voltage till the engines governor catches it.
  9. G650driver, Apr 16, 2015
    #9
    G650driver

    G650driver New Member

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    Very random. Not when a load is applied. I'm embarrassed to say this but I might have found the problem. I was filling the batteries and found some corrosion. I sprayed some stuff and cleaned up the exterior a little and that caused a big improvement in the generator fluctuations. I suspect that if I do a thorough cleaning of the battery terminals the problem will go away. Could I be right?
  10. Capt Ralph, Apr 16, 2015
    #10
    Capt Ralph

    Capt Ralph Senior Member

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    If this is the old OhNo 7.5, 2 cylinder monster? I remember a big electro/mechanical run mechanism under the front of the motor. Bad electrical connects may cause a problem here. Since it's under both the OhNo water pumps.
    The electrical end of that beast can get ugly in a hurry and not many (if any) parts are still around. This beast has a crude exciter and no regulator. Also has brushes so don't spray WD40 or paint in the electrical end.

    If you are looking for a tech, look for an old (old) guy. This unit is older that most of the younger techs out there that won't have a clue.
  11. Pascal, Apr 17, 2015
    #11
    Pascal

    Pascal Senior Member

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    Yes, this is true but many people think that adjusting RPM will affect voltage when if fact it affects frequency.

    Which is why I said "directly" :)
  12. Capt Ralph, Apr 17, 2015
    #12
    Capt Ralph

    Capt Ralph Senior Member

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    The gen set has to turn 1800 rpm( for 60 Htz), It is up to the governor to maintain 1800 rpm. When you apply a heavy load, the governor offers more fuel to maintain that rpm. It does not speed the gen set up.
    When dealing with old / weak gen sets, sometimes folks turn up the speed a few rpm. This is NOT a correct fix but covers up the inevitable, your engine is weak and needs service if it can NOT carry the designed load.

    Bluntly said, do not crank up the engine speed to recover from lost power. There are other issues...

    Your in N Ga? Where is da boat?

    ,rc
  13. G650driver, Apr 18, 2015
    #13
    G650driver

    G650driver New Member

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    I agree with all of that. The engine is not having trouble carrying the load. It's a fluctuation problem and I think I've found the problem with corroded batts. I'm traveling now but I'm hopping I've found the problem.
  14. G650driver, May 6, 2015
    #14
    G650driver

    G650driver New Member

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    Thanks for all the help. The generator is working fine now. After discussing it with Onan, they diagnosed the problem correctly. A new circuit board. $450 and all is well. Easy to do myself. Thanks again. I'm sure I'll need more help in the future.
  15. G650driver, May 20, 2015
    #15
    G650driver

    G650driver New Member

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    The generator is fixed. Had to buy a new card for the voltage regulator. $450 from Onan. Easy fix. I'm glad I picked the correct part first because the next step up would have hurt. . Thank you all for the input.
  16. Capt Ralph, May 20, 2015
    #16
    Capt Ralph

    Capt Ralph Senior Member

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    So, it was not the old 7.5 beast but a latter model with a later model voltage regulator.

    Glad your problems were resolved.