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Topic: Onan Generator Frequency Adjustment?

Posted By: bmppbounder on 02/14/05 11:36am

the output frequency of my '02 onan marquis gold 5500 generator has increased slowly over the past 1 1/2 year. for the first year of its life, it had 61 hz unloaded and very nearly 60 hz under about 3 Kw load. now, it has about 63 Hz unloaded and the frequency drops to 61 Hz as load is increased to 3 Kw. all frequencies are consistant, with no surges or cyclic changes. voltage remains at about 120-121 V under all conditions. my frequency meter is properly calibrated.

it starts aok and it has always had monthly 3-4 Kw, approximately hour long load runs. it has about 150 hours total run time.

is there a frequency adjustment to reduce output to 60 Hz?

36 ft. Bounder
ford V-10
two 750 kawasaki vulcans in bed of toyota tacoma toad

Posted By: TimHayden on 02/14/05 12:18pm

As long as this is not an inverter type (and I don't think that it is) the frequency is a function of the speed of the engine. For 60 HZ, the speed is either 3600 rpm or 1800 rpm - depends on the electrical poles in the generator. The speed you have is not important - you will have to adjust the governor to slow the engine speed down a bit - therefore lowering the frequency.

Posted By: travelclan on 02/14/05 12:59pm

My onan book calls for 63hz no load, which will end up being 60 hz under full load. Your data looks fine. I would worry more about being less than 60 hz ,a little over is no problem. More is better than less. Frequency on my unit is controlled by engine rpm.

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Posted By: itsasecret on 02/14/05 01:39pm

It broke in and is now running correctly. You will never adjust that to exactly 60 HZ.

2004 Mandalay 40B , four slides, 350 Cummins/Freightliner.

Posted By: skills4lou on 02/17/05 08:50pm

What kind of frequency meter do you use to test this, and how much did you pay for it? I want to be able to check mine, but as far as I know my multimeter will only test for volts. Thanks!

EDIT: I guess today the search function is working for me. Found my answer. Looks like I'll be looking for a Kill a Watt soon.

* This post was edited 02/17/05 09:42pm by skills4lou *

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Posted By: hndymn on 12/30/05 09:40am

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
1/4 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: kg5388 on 12/09/06 09:19am

please allways post the MODEL number and make sure on an onan you post the last letter of it as that is the spec letter of the genset

you realy need a load bank to set the governor for the full load settings

Before you adjust anything order a manual from onan or cause there are settings that if you adjust and get it wrong you will spend forever trying to correct it and just keep making it worse until you finally take it to the shop and spend a couple of hundred bucks when you can buy a $20.00 manual.
we tell the new guys at the shop if you feel the need to adjust this governor setting here or that governor setting there DON'T come get me because it can be a pain in the butt to fix

Posted By: 1146 on 12/31/05 09:01am

The new Onan RV GenSet line have changed from the old twin cylinder opposed engine coupled directly to the generator, to a new V-twin that belt drives the generator. The old 1800 = 60hz doesn't apply anymore.
The Gold is carbureted with mechanical governor control while the Platinum is fuel-injected and uses an electronic governor control.
Even though they are both voltage regulated, the frequency is still a function of generator/engine speed.
What you want is 60hz at full rated load - in this case, 5.5kw. At no-load you don't what to go above 63hz as a lot of your electrical appliances are frequency sensitive.
Make sure that the carb idle screw is not touching the throttle arm, than look at the governor arm coming out of the engine block, there is a governor spring and adjustment screw attached to it. By turning the screw in the direction that slackens to spring, you will reduce the no-load speed/freq. but make sure that the full-load frequency doesn't drop below 60hz.

Wayne & Phyllis Manning
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2005 Jeep Grand Cherokee 4x4

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Posted By: Tomj200 on 12/30/05 08:01pm

If I recall, the correct Hz speed is 60 +/- 5% which is 57 Hz to 63 Hz. Yours seems fine to me.

Posted By: MELM on 12/30/05 06:47pm

I learned another way to measure the gen frequency from posts a long time ago.

If you have an old AC powered clock with a second hand, it is dependent on the frequency. With the gen running, compare the second hand to your watch. If the clock does 61 seconds while the watch does 60 seconds, the gen frequency is 61 Hertz.

Some microwave ovens also use the AC power for their clocks. Ours has a "countdown timer" function, and I use it to check the gen. If it counts 60 seconds while my watch does 59, then the gen is 61 Hz.

Actually, I use 2 or 3 minutes to minimize the error in reading both...


Posted By: Generator Jim on 12/09/06 08:12am


IF your unit has an electronic governor, there is no setting other than the idle stop.

IF you have the two cylinder opposed piston engine, the first thing to check is the idle stop screw. It is at the top of the carb and the screw bears on the throttle lever cam. To set it, pull and hold the governor rod to slow the engine and turn the screw to get a reading of 100 volts or 55 Hertz. Putting some thread locker on the screw before adjusting will help hold it in the future.

IF a mechanical governor, there is a spring under the black cover that can be adjusted near the carburetor by a Phillips screwdriver. Loosen the spring to slow the unit down and tighten the spring to speed it up. The factory setting is 62.5 at no load and 58+ at full load. I would set the unit at 60 Hertz with the load you normally have on the unit.

IF you have the vertical 2 cylinder V engine, the settings are almost the same except they are on the front of the engine.

Listing the model number of your unit would have helped to get you more precise procedures.


Jim & Jane Latour
08 Chevy 3500HD, crew cab, dually, Duramax/Allison
Crossroads Cruiser CR305SK14, Onan 3.6KY
Retired AF CMS (E9) Power Generation and Onan RV genset Level III tech
Grand Strand Sams

Posted By: Mooseeye on 12/09/06 07:53am

In answer to the question about what kind of meter to use to read / adjust the genset frequency, ExTech makes several models that measure frequency, and most for under $100. I have an ExTech mini RangeMaster that I carry in my motorhome at all times.

Gary "Mooseeye" Burkett
'94 Winnebago Suncruiser


2013 Fleetwood Bounder 35K

Posted By: mr. ed on 12/30/05 04:54pm

skills4lou wrote:

What kind of frequency meter do you use to test this, and how much did you pay for it? I want to be able to check mine, but as far as I know my multimeter will only test for volts. Thanks!

EDIT: I guess today the search function is working for me. Found my answer. Looks like I'll be looking for a Kill a Watt soon.

You can also purchase an inexpensive Radio Shack Digital meter that not only reads frequency but also volts, amps and resistance. It will probably cost around $30 or so. If your frequency is just slightly off (by a few Hz) it won't make much difference except that any timing circuit (such as in the microwave oven) may run slighly off kilter. Shouldn't be enough to worry about, though (you may also note a little "waviness" on a TV picture, but again, it's not too intrusive or of any real importance).

Mr. Ed (fulltiming since 1987)
Life is fragile. Handle with prayer.

2007 Hitchhiker II LS Model 29.5 LKTG (sold)
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