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Generator Duty Cycle

Discussion in 'Generators' started by John B, Apr 14, 2004.

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  1. John B

    John B Senior Member

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    This is a question I haven't been able to track down an answer on.

    My boat has two generators: Kohler 60hz 20kw.

    Often we will drop anchor some place nice and be at anchor for a few days at a time. 90-100% of the time I will have gen sets running for the air conditioning, refrigerators, TV, music, etc. Usually it is close to 100% of the time. Same is true while we are underway.

    I haven't been able to track down how long I can run a generator for continuously. Rightly or wrongly, I will run one for about twelve hours and then switch to the other for the next twelve hours. Manuals do not have anything on this, but do recommend a cool down cycle not under load before the generator is shut off.

    My question is, how long can a generator run for continuously before I should switch over to the second generator?

    Also, approximately how much fuel does a generator consume (GPH)? I can easily be away from shore power for the bulk of a week at a time and am largely in the dark as to fuel consumption attributable to the boat's generators.
  2. John B

    John B Senior Member

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    I found fuel consumption specs for these generators:

    Load GPH

    100% 1.49
    75% 1.24
    50% 0.83
    25% 0.57
  3. diesel

    diesel New Member

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    You can easily run your gensets until you run out of fuel. The engines are overpowered for their application. In some other applications, these engines turn faster than 3300rpm. You gensets are turning 1800rpm so even at full load they are relitavely unstressed. The cool down period under no load is strictly to cool down the armature, not the engine. If you ever have an overheating problem in either the generator or the engine, you have another problem other than continous use. These gensets will shut down before any serious damage has happened if an overheat or low oil pressure has occurred. What a lot of my customers do is run one genset until it needs its service(oil, impeller, etc..) and then switch to the other until its service. But what your doing is fine to.
  4. Capt. Joe

    Capt. Joe Guest

    Good input from diesel...run it until it needs servicing - it was designed to do just that.
    I can add however, that your most concerne should be in regards to approriate loading of a generator. Not a concerne of overloading, but under.
    Underloaded, you will mess-up the cylinder walls and produce premature loss of compression.
    That is why when you are specking out a genset, chosing larger than your AC requirements can be counter productive. Best is when you can have one small and one much larger genset, and use them according to load needs.
  5. JHA

    JHA Senior Member

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    ....Or install a load bank.
  6. John B

    John B Senior Member

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    Thanks to all for the answers on this.

    What is a load bank?
  7. diesel

    diesel New Member

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    It is a static or variable independent load usually made up of a series of carbon discs which load your genset to avoid the cylinder glazing as indicated above.
  8. CaptPKilbride

    CaptPKilbride Senior Member

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    Live in Maine, work in the Gulf of Mexico
    When I used to run a yacht with 2 generators, I generally liked to switch back and forth every 24 hours, for several reasons:

    1. When on charter, the heaviest current loads were at the end of the day, when the guests were all showering, hot water heaters were kicking in, and the chef was cooking up a storm... I usually had to run both generators together and split the load for a several hour period. So at the end of the heavy draw period, I would leave the new one running carrying the whole load, and shut down the one that had been running the previous 24 hours.

    2. 24 hours is about the longest I felt comfortable running an engine without being able to check the coolant and oil levels. And, I liked the idea of giving the genset a full once over before starting it for the 24 hour period to come.

    Patrick
  9. brianwill

    brianwill New Member

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    Ditto everything aaid above. Geberators have problems due to not being run enough and not having enough load on them when they are being run (about 80% of the rated load is a good load on the genny).
  10. JHA

    JHA Senior Member

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    I ran 6 cyl. Deutz gennys for 12 days at a time during a trans-pac. No real problem - just added oil as needed while it was running. Then switched to the opposing genset. I had a freshly maintained (read oil & filter change + maintenance, belts, pumps etc...) ready to go every 13th day. By the way - watch how you load your genset - I don't recommend dumping a full load on it all at once eg: A/C compressors. Let it warm up first then slowly switch the various systems' load over to it one at a time.
  11. Northern Lights

    Northern Lights New Member

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    continuous duty rating

    Most generators built for marine service are rated continuous duty. This rating is at full load. Some of the manufacturers of 3600 RPM machines publish two ratings. They publish a higher KW rating that when you read the small print discover that that rating is limited. This is stand-by rating. These rating should be clear in your technical manuals that came with your machines. If you do not have access to the manuals contact a dealer for the info.