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Old 10-13-2017, 02:48 PM   #1
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Is a slight generator surging normal?

Hey guys. Last weekend we slept on the hook for the first time in our new to us Mainship 31. The PO never ran the generator and Iíve had issues with it because of it. All it needed was a fuel pump and new plugs. Now she starts up and runs great. We probably ran it for 12 hrs and it ran both ACís through the night and then one AC and one stove the next morning.

Anyway, the only thing is when an ac unit kicks on, it obviously loads the generator. It would bog under the load, then recover, but it sounded like the governor was overshooting then undershooting. It would cause the engine to surge a few times before calming down.

Before I start chasing things, I wanted to see if thatís normal or not.

Itís a gas Kohlr 7.5 genset.

Iím tbinking about running a tank of Lucas fuel injector through it. I want to do that for the mains anyway.

Since I know itís going to come up, I did a ton of research about running the generator while sleeping and I determined ours to be safe. Itís located outside the main cabin and we have two brand new battery powered Co2 detectors that I tested right before bed.

Thanks for any help.
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Old 10-13-2017, 03:10 PM   #2
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Steve91T, what you are describing is called "hunting" and is not abnormal. Some governors react to change quicker than others. So long as when the load is applied and the generator hunts a little before settling out, it is likely ok. If it hunts continuously then that would be a problem IMO and should be looked at.
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Old 10-13-2017, 03:18 PM   #3
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Yes, pretty normal as described. AC's put a large startup load when they kick in the compressor, and then a lesser load right after, thus causing the genset to "hunt".
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Old 10-13-2017, 04:23 PM   #4
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I just installed soft start kits on my a/c units and it made a HUGE difference on my generator. I would highly suggest to everyone that they have these installed because it actually gives you more power for other things and makes your generator and a/c units last longer. Go online and read about them!
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Old 10-13-2017, 08:48 PM   #5
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Gas generators that have seen little use often have carburetor issues. This will show up first as lagging when new loads come on, then hunting and finally inability to reach full capacity. The first test you should try is max capacity. If the generator can not reach max capacity and is lagging it sounds like a carburetor issue.

What you experienced is not normal even for gas generators.
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Old 10-14-2017, 06:29 AM   #6
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Surging aside, is it wise to run a below deck level gas generator all night?
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Old 10-14-2017, 07:58 AM   #7
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I run mine at night. But i only run the ac where we sleep. Carry spare impellers!!!!!!!
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Old 10-14-2017, 09:17 AM   #8
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Quote:
Originally Posted by tiltrider1 View Post
Gas generators that have seen little use often have carburetor issues. This will show up first as lagging when new loads come on, then hunting and finally inability to reach full capacity. The first test you should try is max capacity. If the generator can not reach max capacity and is lagging it sounds like a carburetor issue.

What you experienced is not normal even for gas generators.
First, he described it as a "slight" surging, and depending on the start up load of the AC, the phenomena is fairly normal and seen on diesel gensets as well. And I don't think Kohler has made a carburated generator, maybe ever.
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Old 10-14-2017, 12:25 PM   #9
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Quote:
Originally Posted by tiltrider1 View Post
Gas generators that have seen little use often have carburetor issues. This will show up first as lagging when new loads come on, then hunting and finally inability to reach full capacity. The first test you should try is max capacity. If the generator can not reach max capacity and is lagging it sounds like a carburetor issue.



What you experienced is not normal even for gas generators.


Agree. A classic controls stability problem. In a generator, the design goal is constant ac frequency, which in most gensets, means constant rpm. If the motor has reduced torque/hp, then the control loop can loose some ability to maintain frequency.
Did you know there are large countries that can not maintain frequency of ac mains due primarily to excess load for their gen capacity.
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Old 10-14-2017, 12:30 PM   #10
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Note that there will always be a transient condition at the point of rapidly changing loads. The engine will always slow (or rev up), the amount of which is dependent on rotary momentum (high is better) and inertia of any mechanical governor (low is better).
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Old 10-16-2017, 10:49 AM   #11
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Thanks guys for the help.

The generator is carbonated and I’ve verified the automatic choke is working properly.

I’d be willing to bet that the carb could use a cleaning since it saw such little use. Like I said, I want to run some Lucas fuel injector cleaner for the mains anyway, so I’ll make sure to run the gen with that stuff in the tank. That and more use will probably help the hunting.

I’m definitely going to start shopping for a soft start kits. That would probably make a huge difference.

Thanks guys!
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Old 10-16-2017, 11:29 AM   #12
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The generator being carbonated would explain the co2 detectors.
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Old 10-16-2017, 11:40 AM   #13
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The generator being carbonated would explain the co2 detectors.
good one! But, then that opens up a lot more questions
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