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Generator Output Hunting?

Discussion in 'Generators' started by Ozzie, Oct 18, 2011.

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  1. Ozzie

    Ozzie New Member

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    Hello all,
    Was checking out a generator on a boat today and test ran it fully loaded. The volt meter was rhythmically fluctuating about 50v, from 100-150 on the meter. Rope lights, air con controls and power led's on the panel were dimming in sync. It looked like what a diesel sounds like hunting for fuel. The gen itself was not hunting.
    There were no load issues on shore power.
    Any ideas as to the cause?

    Thanks in advance,
    Ozzie
  2. Capt J

    Capt J Senior Member

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    What brand, make, output generator are we talking about? Gas or diesel? Are you sure that the engine rpm's were staying the same? Because it could be varying engine rpm's. If the engine rpms are the same, it can be the voltage regulator on the generator end going bad possibly.
  3. K1W1

    K1W1 Senior Member

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    Hi,

    I have been told on here I don't speak the preferred version of English, regardless of that I can read any version and the statement above takes some deciphering.


    Not really until you can provide a bit more info as requested by CaptJ in his post above.
  4. Ozzie

    Ozzie New Member

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    Hello,

    K1W1 I understand your dilemma as I too have difficulties with English as my first language.

    " The Volt meter gauge needle looked like what a diesel sounds like when it is hunting for fuel."
    Hopefully that helps, it's similar to the S.A.T. test questions: An elbow is to an arm, as a knee is to a ________.

    The genset is at work so I'll post the brand/model/output later.
    As i have never seen this happen before on any genset I was betting on a generic "yeah I've seen that before" response.

    CaptJ it definitely was not the gen varying in RPM; it is a diesel.

    And just so that we aren't flooded with responses, the answer "Leg", though correct, is not the answer that I need. :D

    Thanks for replies
    Ozzie
  5. K1W1

    K1W1 Senior Member

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    Hi,

    If it is just the gauge fluctuating wildly I would suggest that you use a good Test Meter on the Genset Cables and see what you get there.

    Your problems could be a faulty instrument in the panel, a loose wire, a AVR Fault, a dry joint ( not the kind wrapped in paper).

    If the lights and such are up and down then it is pretty certain your engine speed is varying as well unless all is fed through a UPS.

    With so many possible causes getting as much info as possible will no doubt help narrow those down.
  6. Marmot

    Marmot Senior Member

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    If the installion includes a frequency meter it is a no-brainer to determine if the rpm is fluctuating. If it is solid on 50 or 60Hz then you can exclude engine problems.

    IF the voltage is unstable with a load and with no load then it may just be simple adjustment of the stability pot on the AVR.

    And, as K1W1 pointed out, it could be loose or corroded connections on the AVR or on the excitor itself.

    Does the installation include a ground detector?

    It sounds like time for someone to sit down and read the manuals. RTFM should be the first step in troubleshooting.
  7. Kafue

    Kafue Senior Member

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    Okay, I'll stick my amateur nose in;
    Turn off the Aircon and see if it still happens.
    Then the fridges and freezers one by one.
    Could well be a compressor coming on and off for some reason.
    Just my 2c.
  8. Pascal

    Pascal Senior Member

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    generally speaking...

    the first thing to be sure is if the engine RPM is constant or not. if voltage is that irregular, i'm pretty sure you'd have noticed if there was an RPM issue caused by dirty filters, governor, etc...

    RPM directly controls frequency not voltage so chances are the problem is with the voltage regulator.

    how often does the cycling occur and does it occur with no load? reason i'm asking is that a bad AC compressor could put such a draw on starting that voltage will drop 20 or 30v to the point where the compressor control (if electronic) will turn it off then it may try again. it's a long shot but based on the lack of details, it's still something worst considering.

    Obviously, don't attempt to troubleshoot this with loads connected to the genny, this will damage equipment on the boat.
  9. Capt Fred

    Capt Fred Senior Member

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    I was working on a 5 KW gas Westerbek which was hunting under the load of a water heater, voltage and RPM were varying, I eliminated everything as the possible cause, fuel, RPM trip, over temp, oil pressure and finely disconnected the mechanical governor and the RPM and voltage stopped hunting. The client did not want to spend the $$$ on a new governor so the problem still exist.
  10. Marmot

    Marmot Senior Member

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    This is why RTFM applies. Some troubleshooting procedures require the system to be operated under load. Read The Freaking Manual and ignore 99 percent of what you read here because most of it has been nonsense.
  11. Capt J

    Capt J Senior Member

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    I had this happen on a generator and it was the voltage regulator, which appropriately fried itself 5 minutes later. The voltage dropped and spiked, with no load on it whatsoever. Run the generator with no load and see if it's still doing it. It could also be a loose electrical connection.
  12. Pascal

    Pascal Senior Member

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    yeah well i kind of worry when i read about voltage jumping up and down by 50v and someone leaving a bunch of devices affected by this!

    so first thing first... make sure votage AND frequency are ok with no load and then start putting loads on.
  13. Ozzie

    Ozzie New Member

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    Thanks for all the replies,
    Unfortunately I wasn't able to get the model info on the genset.
    We've got a fair number of boats here that we take on as owners decide they want to sell. And it can get busy.
    This was a new addition that I was doing a systems and general condition report on. It lives on shore power and won't be loading the genset until this issue is resolved.

    I had been planning on troubleshooting, but until I can get a work order and time I was hoping to get a mental jump on where the problem most likely existed.
    Having done the systems checks I know that all my other high load draws are working correctly. And again the RPM's were NOT varying, so it must be an electrical issue alone.

    As far as manuals go I managed to find volumes A-E, but not the F one.

    Thanks
  14. Marmot

    Marmot Senior Member

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    If you have A then look under AVR for stability pot.
  15. Globetrotter76

    Globetrotter76 New Member

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    Hi Ozzie

    I agree with Marmot, I had a similar problem onboard the vessel I work on. I was running two Generators on load and my alarm and monitoring system had a high Amps Alarm on one of the generators. I started the third generator loaded it up, dropped a few high loads like the AC plant while I did a troubleshoot on the generators, I let them run unloaded while I observed the Power Meters and noticed that the one generator had voltage of 209 which was correct the other generator ran at about 202v, I stopped the generator in question and since I had a spare AVR I changed it out and adjusted voltage on trimpot before loading up again and problem solved.

    I've also had problems with generators hunting and the frequency not staying constant, In that case I had a bad Electronic Governor Controller, after adjusting trim and stability trimpots it still did not want to stop hunting. I checked all the fuel side checks and actuator etc and ordered a new EGC, installed and solved that problem.

    Anyways good luck with the troubleshoot
  16. Capt Ralph

    Capt Ralph Senior Member

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    Hello Ozzie
    Fixed yet? Look forward to the outcome and how you found / resolved it.
    ,
  17. Ozzie

    Ozzie New Member

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    Update

    Hello and thanks again for the replies,

    So far the problem remains, but this time it's different. I was on the boat last week and tested the gen again. This time the voltage was stable, but only putting out 102VAC.

    Which is probably the exact issue that Globetrotter76 had. Is it normal for an AVR to cause 2 totally different situations such as wildly fluctuating voltage and then the next time just low voltage?

    KOHLER
    Model: 11CCFOZ
    Rewired to: 62.5hz 220VAC



    Again, at this point I am only observing and reporting the issues that I have noticed with the output of the gen, and I am only seeking the advice as to the cause from the knowledge bank here on YF.

    Thanks again,
    Ozzie
  18. Capt J

    Capt J Senior Member

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    You need to check rpm's and verify rpm's of the generator, it sure sounds like a fuel restriction to me. What were the hertz when it was putting out 102 vac? If both the voltage and hertz are low, the generator is simply not turning enough rpm's. Honestly, by the questions you're asking it would behoove you to hire a factory trained mechanic to fix this persons generator.
  19. Marmot

    Marmot Senior Member

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    That thing isn't "rewired" to a frequency, there are a couple of potentiometers that set the V/Hz cut in for the voltage regulator but 62.5 Hz isn't a wiring choice. If that is what it is running at under no load that is OK more or less.

    That little generator has a weird little control and regulator system that you need a flashlight to troubleshoot ... seriously, the flashlight is used to fool a phototransistor on the exciter, if you run with the cover off the end of the generator you can get all sorts of weird things going on. Yours is on right?

    Either get the service manual and be prepared to sit down and read it for an hour or so before thinking about opening up any covers. If you still feel you can handle it go for it, it ain't rocket science. If you don't want to fool with it, the Kohler shop has a tester and a good tech can troubleshoot it for you very quickly. Chances are it is just an adjustment on the AVR but the symptoms could indicate a couple of other issues which are easy to test but you can't do it without a manual.
  20. dennismc

    dennismc Senior Member

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    Generator

    Not to disagree with the Marmot, but i thought the CCO series had a PC board and adjustments were severely limited by end user ??