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Topic: Generator surges under load

Posted By: OSCBRADLEY on 12/10/11 09:42am

Hi All,
On my recent trip to Florida I started up the Onan and while it ran fine with just powering the TV and lights, it continually surged from high to real low power when I used the microwave or cabin heat. I stopped at a rest area and adjusted the throttle to where the RPM's seemed normal and the surging stopped, however, as soon as the microwave was off or the heat kicked off the generator would race and I would have to go outside and adjust again. Eventually I just turned it off in fear of hurting something electrical. Has anyone experienced this and if so what was your repair solution? Thanks.


2016 Winnebago Minnie Winnie 25B


Posted By: Son of Norway on 12/10/11 10:00am

What type of Onan do you have and how many hours are on it? I always start with checking fuel and the carburator. How often have you been using it and do you use a fuel preservative? I've seen some others on these forums recommend Sea Foam. I would check these things first before moving on to sensitivity adjustment.

Miles


Miles and Darcey
1989 Holiday Rambler Crown Imperial
Denver, CO



Posted By: MountainAir05 on 12/10/11 01:05pm

You never want to mess with the adjustments for speed as it changes the output of the generator. You need the meters on hand to do much of this. This is only a general statement. It a little different per model. But since you have already change the setting, then

If you need to adj the governor what is the correct procedure?

* On the speed/frequency issue: first, take a close look at the genset when it is running with no load - the idle stop screw should NOT be touching, i.e. pressing the throttle lever back against the idle stop should lower the speed to 55 hz, and there should be visible space between the screw and the lever. Adjust this as necessary. * Next, with the genset stopped, unclip the governor linkage rod from the throttle lever and check that the rod goes in the hole on the throttle lever with the throttle lever just short of being wide open throttle. Adjust the rod length if necessary by loosening the locknut on the other end of the rod (where it threads into the ball and socket joint), turning the rod into - or out of - the joint as needed, then re-tighten the locknut and clip the rod back into the throttle lever. * Looking at the governor mechanism, you'll see an arm extending outwards, pivoting on a shaft coming up vertically out of the engine, with the ball and socket joint on the end closest to you. About 2/3 of the way down the arm, you'll see a spring extending to the right, with the left end hooked to a link that's threaded on a screw mounted in the arm and the right end hooked to a threaded rod that goes thru a stationary bracket, with a nut on the other side of the bracket. This nut is the speed adjustment nut - by controlling the tension on the governor spring, it controls the speed of the genset. * The screw mounted in the governor arm is the sensitivity adjustment screw - by moving the point where the governor spring is attached to the arm, it changes the governor sensitivity. With no load, adjust the speed adjustment nut for 62-63 hz. Apply full load - the speed should be at least 58 hz. Spec calls for 2-4hz drop from no load to full load, but in my experience, trying for anything less than 3hz makes the gen unstable at some load levels (whoop whoop whoop as it accelerates/decelerates but never settles on a stable speed). If your drop from no load to full load is more than 4hz, adjust the sensitivity screw counterclockwise by 1-2 turns, re-adjust the speed nut, then test drop under full load again. Continue until no-load to full-load drop is under 4hz. Do note that this presumes carburetor mixture screws are correctly adjusted first:
* With the genset fully warmed up, apply a full 4kw load. Turn the main adjustment inward until frequency drops slightly. Turn main adjustment outward until frequency drops slightly. Locate the point where frequency is highest (approx midway). From this point, turn the adjustment out another /4 turn. Remove the load. Allow genset to stabilize for 30sec-1min, then turn the idle adjustment screw in _slowly_ until frequency drops and engine begins to run rough or starts hunting. Back out the idle adjustment screw as required for smoothest running/highest frequency without hunting (may take 1/8 - 1/4 turn out from highest frequency to keep set from hunting on sudden load removal). Test with various loads, and transitions between various loads, to ensure stable operation under all conditions


Posted By: 4*phun*2 on 12/11/11 06:23am

Fuel filter? Air filter? Old gas?


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Posted By: OSCBRADLEY on 12/11/11 06:44am

550 hours on the genset, new air filter, very recent oil change but I believe the fuel filter is original. I thought about the gas like everyone has mentioned but it's my understanding that the generator draws directly from the motorhomes gas tank which received 4 fresh tanks during the trip. I didn't know I wasn't supposed to mess with the throttle linkage so looks like I may have to call in a certified Onan mech to fix my repairs....some things never change haha...


Posted By: ryanallie1 on 12/11/11 08:23am

Hi All.

The Fuel Filters are pretty cheap, and should be changed often. On our Generac 5.5G Generator, our owners manual says to change the Fuel Filter every 100 hours. I think at 550 hours, you are way over do. You should also run and exercize your Generator once a month for best performance. Or run your Generator dry to provent Gas problems. It will also help to keep your fuel system clean and not let it gum up. For long periods of storage, you should dump a bottle of "Sta-Bil" in your Motorhomes Gas Tank. "Sea Foam" to the rescue. Sea Foam does a great job of cleaning up your Generators fuel system. I don't have an Onan, but a Generac 5.5G Generator in our Motorhome. I use St-Bil in our Motorhomes Gas Tank. I also keep Sta-Bil in our Gas Can for our Honda's. Every now and then, I will run some "Sea Foam" though all of our Generators. The Honda's are about 8 years old now, and we have never had any problems what so ever. Take good care of your Gennerator, and your Generator will take good care of you. Good Luck. Happy Travelss. Dan & Jill


1998-34 ft Rexhall, Rexair SL. 460 EFI. F-53. 7.3 MPG. TST TPMS. HWH Levelers. 5.5G Gen. Convection/Microwave Water Purifier/Water Softner. 2 A/C's. Alarm Systems. Honda EU2000i's W/Kit. Steer-Safe. CR-V W/SMI System. FMCA #F414397 Nam-Vet, 66-67-68&70-71



Posted By: missscarlet9 on 12/11/11 08:52am

I have had the same experience with Onan generators. The solution was simple and may or may not apply to your situation.

My problem was dirt on the linkage of the governor. I used to travel on a lot of dusty back roads back in the day of back woods camping. I found that the dust effected the free movement of the governor linkage causing the surging you describe. A very thorough cleaning and lube with silicone spray lubricant was all it took to fix the problem.


Livin' the dream!



Posted By: John339 on 12/11/11 09:28am

I agree with ryanallie1 about the Sea Foam.
Inexpensive and will clean out the carbon and gunk in the gen set.
Recommended by Onan.
I put some in a spray bottle and took off the air filter.
While running spray into the air filter until the gen set stops.
Let it sit for an hour or so and start it up.
Stay away from the exhaust pipe because a lot of junk will shoot out.
Don't ask how I know.


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Posted By: roam1 on 12/12/11 07:34am

Florida is "sea level"
Where is your "altitude" adjustment at ?(if you have one)
should be at zero


Posted By: OSCBRADLEY on 12/13/11 12:29pm

Altitude was set at zero...I'm a little confused about running the generator "dry", in my thinking I cant do that can I since the gen draws its gas from the motorhomes fuel tank? I do run the generator under load for at least 1/2 hour every month. I will change out the fuel filter and clean linkage as suggested.


Posted By: khahuna on 12/14/11 01:06pm

My Onan (propane 6.3) was doing the same thing ... changed plugs, oil and air filters and oil. Turned out to be the slip rings needed cleaning.


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Posted By: ryanallie1 on 12/15/11 06:38am

OSCBRADLEY wrote:

Altitude was set at zero...I'm a little confused about running the generator "dry", in my thinking I cant do that can I since the gen draws its gas from the motorhomes fuel tank? I do run the generator under load for at least 1/2 hour every month. I will change out the fuel filter and clean linkage as suggested.


Hi All.

You can add an inline shut off valve, on your Generators fuel line. Its a very simple Mod to do. Good Luck. Happy Travels. Dan & Jill


Posted By: donandmax on 12/15/11 02:59pm

John339 wrote:

I agree with ryanallie1 about the Sea Foam.
Inexpensive and will clean out the carbon and gunk in the gen set.
Recommended by Onan.
I put some in a spray bottle and took off the air filter.
While running spray into the air filter until the gen set stops.
Let it sit for an hour or so and start it up.
Stay away from the exhaust pipe because a lot of junk will shoot out.
Don't ask how I know.

At my local NAPA store Sea Foam is not cheap it would have cost me close to $30.00 to treat 75 gals. of gas. I used Stabil instead and it was half as cheap. Sea Foam is a great product though just a little pricey IMHO


If it aint broke fix it till it is


Posted By: Mikeeg on 12/17/11 09:06am

The Alt. Adjuster is probable the problem slowly turn it up and Mine smoothed right out. You are at sea level but just a small adjustment up should make a difference.


Posted By: roam1 on 12/17/11 04:22pm

Mikeeg wrote:

The Alt. Adjuster is probable the problem slowly turn it up and Mine smoothed right out. You are at sea level but just a small adjustment up should make a difference.

I agree, that's worth a try
a lean engine usually surges, the higher altitude requires a leaner mixture, and vise versa for lower altitude, but those altitude adjustments are not exact, tweek it a bit both ways and see how she does


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