Generator Issue

Last Saturday at College Station, fired up the generator with a light load when shut the bus down. It started up right away, but soon began shaking and causing the lights to flicker. Since it was cooler than I had ever started the genset before, I assumed it might need to warm up a little. Shut it down and re-started several times with same result. It would run fairly smooth for a few seonds and then began shaking. Ended up shutting it down and leaving it alone until I returned home.

Sunday afternoon I started it up at the barn to check things out. It started shaking again, so I kicked off the load switch which caused it to smooth out. After it ran for a few minutes and came up to temperature, I switched the load back on and it ran fine. Ran it for 2 hrs while doing some other work around the coach with no problems.

Tonight I went out there to do some work on the coach. Pulled it out and fired up the genset. started shaking and causing voltage surges and flickering. Generator output voltage varied wildly on the Trace display 100 to 145 volts. This time it wouldn't smooth out when loaded even after it was warmed up. Never could get it to stop shaking when I flipped on the load switch.

Initially thought it might be a fuel problem, then thought it might be a temperature problem and now am wondering if it is a voltage regulator or something like that (Leon at Marathon suggested contacting Detroit/Kohler but guessed voltage regulator)? When unloaded, it still shakes a very small amount - once it is loaded it starts to vibrate after a few seconds and almost gets into a harmonic type of action.

Ideas? Tomorrow I am going to change out the fuel filter. I keep thinking it is sourced on the generator end, but with the slight amount of shaking, still wonder if it is in the motor and then gets magnified when loaded (not big loads here either 10-15amps)?

Kohler 20KW with 3200 hrs.

This is an overly simplistic guess and may have nothing to do with your problem.

Our generators like to be run, and to be run hard. Loading a generator with a couple of air conditioners doesn't even come close to loading it. Running at light loads eventually dirties up the injectors and cylinders.

The cure, if that is the problem is simple. Run the generator long and steady and keep adding load. If you can get it running smoothly as your loads are increased to a total of 60 or 70 amps it will clean itself up after several hours.

Any diesel engine that is idled or run at very light loading over time is going to stumble and may even shut down if all of a sudden it is loaded.

Gordon, before you do anything else, do this. Change out the fuel filter and the air filter. The air filter is more than likely the problem, but change them both. Your problem will go away.

Ted,
I checked the air filter last night and it was very clean. I am going to change the fuel filter today.

Jon,
I have put almost 200 hours on the generator since June and almost all at high A/C load dry camping in the heat. Last trip of that type was 4 days running non-stop in Alabama in Sept. In late Oct I pulled it out and turned on 2 A/C's and ran it for an hour to excercise it.

I am worried about the vibration as the electric load kicks in and voltage fluctuation. Just don't have any experience as to whether the voltage fluctuation will cause a problem for my inverters etc.

Maybe we are talking about two different things. The stalling or stumbling, meaning the generator is failing to maintain a steady RPM sounds like a motor problem.

That is a guess on my part because it seems like when you add load the motor cannot handle it, and lugs down and attempts to get back to its normal steady RPM. That of course affects the generator section output.

But I can also envision a generator section with a problem that causes it to intermittently put out power, with the load and voltage going up and down alternately loading and unloading the generator causing it to act like it has a problem.

If that were happening to me I would start with all loads off, make sure it runs smoothly and then start adding load. If necessary I would add load an AC and heater, one at a time until it either stumbles or runs smoothly. If it stumbles I would stop adding load until it smooths out and then continue adding load.

FWIW the Kohler engine I believe has had fuel pump problems. That needs to be verified because I got that from word of mouth.

It is not the 200 hours of running, but how heavily it was loaded. Unless you were steadily loading it with 60 to 70 or more amps it wasn't even beginning to have a load. It is a 20,000 watt generator and about 90 amps is only half a load. A couple of AC units is 26 amps. Our generators should run 30,000 hours or more with zero problems if we run them hard by making them work for hours on end with those heavy loads. If we do not run them continuously and often heavily loaded they are getting sooted up internally.

Your inverters as well as other devices are not benefitting from huge voltage swings. If during your testing and playing with the generator you want to minimize the potential for damage to electrical devices limit the loads to only those circuits that are less affected by voltage swings such as resistance heaters (toe space heaters, stove, electric BBQ grille, block heater, water heater, etc.) Leave items with complex electronics off such as the inverters, refrigerator, any TVs, etc.) If it runs smoothly with resistance type loads, then start adding things like ACs.

For the moment I will stick with the theory it needs to run hard. Not to be overlooked however is clean fuel filters or air filter. But what steers me away from those is in your first post you loaded it and ran it for two hours. If it was fuel starvation adding that load would have caused it to quit. If it is an air filter situation you would have seen black smoke out the exhaust.

Ok, thanks Jon. I wouldn't call it a stumble as much as it is a harmonic low frequency vibration. Ruummmppp Rummmpppp Rummmmppp (how is that??)

Almost unnoticeable when the generator load switch is kicked out but becomes amplified after the switch is on. Immediately goes away once the load switch is kicked off or returns down to that very low level.

RPM control or governor? Does that mean it runs OK but the RPM varies?

Doesn't feel like RPM control as much as it does load causing the fluctuation.

The more I think about it the more I wonder if it is on the generator end - voltage reg. My Kohler manual shows an adjustment to the voltage range along with a fine tune knob on the voltage regulator. Wonder if that would be worth pursuing if the fuel filter doesn't help. Really getting out of my league there.

There is no down side to playing if you feel it is load related on the generator side. Just shut down everything other than resistance loads. Then load it with the HW heater, engine block heater, stove, cooking grill etc. Those loads have no sensitive electronics and are relatively unaffected by voltage swings.

Will try that Jon. Thanks