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Old 18-01-2013, 15:51   #1
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Onan MDKC 4 kw Gen Frequency

Just completed the sea trial on a trawler with a Onan MDKC 4kw with 3715 hrs generator & the surveyor noted:
Under load the generator frequency was 58.1 hertz. As this is somewhat below 2% low it is advised the generator speed be adjusted to produce 60 hertz under load. The frequency, not under load, is 60 hertz.
Would this be a matter of adjusting the governor & if so can anyone offer advise of doing so? I am not familiar with these units but guess I now own one. Jim
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Old 19-01-2013, 09:45   #2
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Re: Onan MDKC 4 kw Gen Frequency

First off, your genset is pretty close but it should be closer.

Generator output frequency is a function of generator speed. I am not familiar with the MDKC but I do have a 15kW MDJF. On my unit, there is an adjustment screw under the platform that holds the water pump">raw water pump. This screw is unique. There are machine threads in the platform and very prominent Acme type threads with a spring that rides inside them. The spring controls the governor, as I recall.

To adjust, monitor the line frequency and adjust the no load frequency to about 62 Hz. Load the generator while monitoring the line frequency and observe its reduction as the genset loads up. This reduction is known as "droop". More modern gensets have a droop adjustment. Adjust the genset speed so that it produces 60Hz @ 80% of genset rated capacity and you should be ok. If you have a droop adjustment, you should be able to get spot on.
Charlie Johnson
JTB Marine Corporation
"The Devil is in the details and so is salvation."
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