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Old 05-15-2020, 06:18 AM   #1
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AC Panel Lights Flickering When Running Genset

Fired up the the boat and generator yesterday to go on short river cruise. As soon as I did I noticed all the lights on the AC panel flickering, the analog AC voltmeter was also dancing up and down.

I shut it down, and went on the cruise without. Will try to check closer when I have more time this weekend. It appears to be putting out power, as I checked a nearby phone charger, which was working.

Any ideas what might be causing this?
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Old 05-15-2020, 07:33 AM   #2
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I would start by safely checking to see if any of the ground or load lugs are loose.
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Old 05-15-2020, 07:53 AM   #3
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What generator is it? Some are more prone to governor instability that will cause rpm to go up and down, and that can cause volts to go up and down too.
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Old 05-15-2020, 09:32 AM   #4
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When the generator was running, how did it sound? How did it feel (vibration) etc? Does shutting off its main breaker or change any of your answers?

Depending upon your answers there, I have different guesses.

If it sounds normal and feels normal, even with the main ofg, I'd verify the RPMs with a phototach or the gauges and make sure they are steady then sort it from there if not, e.g. air in fuel? Etc.

What make and model is it?

If it is running steady, then I'd check the electrical connections.
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Old 05-15-2020, 07:36 PM   #5
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Kohler 9.5kw diesel. It seemed to be running steady.

I will investigate more closely this weekend
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Old 05-15-2020, 09:01 PM   #6
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What else changed?? Repair work, problems on the dock, etc.

First episode or Has this happened before?
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Old 05-16-2020, 07:07 AM   #7
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The only thing different, is that I asked my wife to unplug the power cord. She unplugged the cord from the power post, but did not unplug from boat when I fired up the generator.
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Old 05-16-2020, 09:58 AM   #8
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Unlikely she did anything which could cause the flickering. Do you have a generator isolator switch or breaker - prevents you from connecting generator back to shore power?? Mine has a mechanical interlock which will not let you close the shore power breaker and the generator breaker at the same time?? (just checking).



Sounds like a corroded ground/common connection somewhere in the generator feed. Good luck troubleshooting it.
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Old 05-16-2020, 10:39 AM   #9
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I had a three year old Westerbeke 5.5 generator with a Mitsubishi diesel engine that had issues similar to yours. Lights flickered, voltage fluctuations etc.

The first fix was a new governor spring repaired on warranty. The generator ran better but speed still hunted and lights flickered under load.

Gallery Marine in Seattle was the dealer and they were unable to find a solution. Westerbeke thought I was imagining the hunting generator speed and thought I was being a PITA. I complained enough that Don at Gallery gave me a new replacement generator and sent my old one to Westerbeke.

Westerbeke tore it down and found an out of round governor shaft that caused the hunting.
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Old 05-16-2020, 10:47 AM   #10
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Could also be a light source causing a synchronization to the sine wave.

An example would be looking at a fan running but the blade seems to not be moving.

Try turning off all lights then look at panel in the dark.
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Old 05-16-2020, 10:48 AM   #11
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Also could be brushes.
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Old 05-16-2020, 10:49 AM   #12
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Thanks for all the ideas. Heading to the boat shortly to check things out.

There is a slide lock to keep from pulling load from generator while on shore power, so I didn't think having cord plugged to boat would be an issue, but that was the only thing out of the ordinary.
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Old 05-16-2020, 11:04 AM   #13
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If you have a digital multimeter that can measure frequency, measure the frequency at the generators output under different loads.

If the frequency is steady, the problem is in the boat. If frequency modulates then the generator is the issue.

You can do the same test using the voltage function on the digital multimeter but I prefer looking at the frequency.
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Old 05-16-2020, 11:05 AM   #14
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Out of round gov shaft- boy that's a weird one!!!
The only real test is to put a scope on the genny's ouput and look at the wave form. (Cheap digital will do it - Best Buy maybe) I have an adapter for my PC Laptop that really comes in handy for quick checks like this. (The big, high speed scope stays in the shop - away from any water!!)

Like Cinnci - Bought an old SEARAY 270 from up there. Use to fly into Blue Ash all the time. Make mine a "two way" !!!
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Old 05-16-2020, 11:11 AM   #15
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Also could be brushes.

Most if not all modern generators are brushless.
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Old 05-17-2020, 10:24 AM   #16
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Many Kohlers (depending on vintage) and the popular Northern Lights 5-6kw use brushes.

But it is rare for the brushes to cause the issue OP described.

To the OP- What model or rough year make is the Kohler?
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Old 05-19-2020, 02:45 PM   #17
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The unit is a diesel Kohler 9EOZ, 1999 vintage.

I checked what I could over the weekend. Nothing fixed. I have contacted a mechanic to look at it, but he is backed up for several weeks...

I did notice that AC appliances are not operating correctly (flickering).
The genset will start via the remote panel switch, but will not shut down. I have to shut down the unit with the start/stop switch on the genset.
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