How do you set RPMs on Onan 2800QG

[rowiebowie]

My '2012 Onan 2800QG generator is only producing as low as 53hz/107 volts when using it to run my new Coleman Mach 8 Plus 15K ac. With no load on the generator, the reading is 57-59hz/119 volts as displayed on my Progressive Industries EMS PT-30X. I plugged it into a coach outlet just to use it as a power monitor. Power Systems monitor shows a/c only has a 12amp draw. I stopped the a/c after about 5 mins. to avoid possible damage.

I did several forum searches, and apologize if this topic is out there, but I couldn't find it.

Nothing in the Onan manual addresses how to adjust the engine speed. From what I can find online, the Hz are a result of engine speed which in my generator's case should be 3600 rpm. All I've seen on my engine's carburetor is an altitude adjustment from 0-10000 ft. I keep it dialed to zero since I live at 18 above sea level. The engine runs smoothly with only a rare stumble.

My questions are:

1) Is the way I'm using the Progressive Industries EMS showing a true representation of power from the generator?

2) Will 53hz/107 volts hurt my new a/c?

3) What kind of adjustment does my Onan 2800QG have that will allow me to adjust the rpm?

Ps. - I recall on shore power our microwave heated water for coffee nearly as fast as our home microwave. But when we ran it on generator, it took at least 1&1/2 times as long to heat water. Is this another indication of poor generator power?
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[r carl]

https://www.manualslib.com/manual/83...page=30#manual

[rowiebowie]

Originally Posted by r carl

https://www.manualslib.com/manual/83...page=30#manual

Thanks. I have definitely bookmarked your service manual reference. I did initially run the new a/c on the generator for about 40 minutes (before I thought to check output using my EMS. I hope I caused no damage.

Good to know it is as simple adjustment as a screw adjustment to the governor. I have a hrs. meter/rpm indicator I can attach to the spark plug wire for future reference, but it will be a pain to have to get underneath the van to check it.

Am I the only one to test the generator output? It seems with all the generator questions out there, I should have found something during a forum search.


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[r carl]

I have one of these plugged into a receptacle on the wall of my camper so I can look at a glance and know the voltage in my camper.

[rowiebowie]

My Progressive Industries EMS was showing enough volts, just the Hz were dropping well below 60Hz. They seemed to drop off worse than the voltage.


After I adjust the Onan, I'll post my results. It may not be a week or so as we aren't planning on our next trip for at least a month, and it's soooo hot right now.


Thanks again.

[Burfield]

I have a Koehler generator and it automatically adjusts the RPM Based on load. Surprised if the Onan does not have this feature. Do not normally want to mess with the throttle screw, over speed will damage the generator. Sound like your governor is not linked to the load demand. Think I would call Onan.

[rowiebowie]

Originally Posted by r carl

https://www.manualslib.com/manual/83...page=30#manual

Originally Posted by Burfield

I have a Koehler generator and it automatically adjusts the RPM Based on load. Surprised if the Onan does not have this feature. Do not normally want to mess with the throttle screw, over speed will damage the generator. Sound like your governor is not linked to the load demand. Think I would call Onan.

Well, now I'm back to square one. The Service Manual link provided in Post #2 is dated 1991, so may not apply to my '2012. It shows a governor screw adjustment for speed.

But thanks to r carl's manualslib.com link, I did find a Service Manual for a '2009 (like mine) and it shows a different sort of mechanical governor that turns from a gear inside the motor (see attached).

I just want to get my genny running at a safe output (volts & Hz) to run my a/c without damaging it. I'm not qualified to get too far into the mechanicals of the generator, so is it time to seek a qualified Onan service center?

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[rowiebowie]

Ok, I had more time to go through the online service manual for my model. In the troubleshooting section I finally found the process for low output and it basically says the following:

1> Make sure the carburetor is properly adjusted (it describes the process).

2> It describes adjusting the governor shaft adjustment (which looks like the mechanical governor in the earlier manual reference provided by r carl).

Getting to carb is not easy, but doable through the access panel. It may be another matter to get to the governor shaft, if it comes to that.

Why didn't I test the generator output back in the early Spring when it was cool? Arhhhhh!


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[Burfield]

You can manually rev up the rpm and see if that brings it up to specs. Look for the carb and find the fuel/air supply lever while its running and move it
If that brings up the amp output you’ll at least know it’s working, and not bad brushes or rotators

[rowiebowie]

Originally Posted by Burfield

You can manually rev up the rpm and see if that brings it up to specs. Look for the carb and find the fuel/air supply lever while its running and move it
If that brings up the amp output you’ll at least know it’s working, and not bad brushes or rotators

Yes, that is what I intend to do. It is the easiest and least obtrusive thing I can try. If I need to adjust the governor shaft or if bushes are corroded, I can always tackle that after the carburetor adjustment or speed screw adjustment.

The carburetor was replaced last Fall just before I bought it. Probably gummed up from old gas and the lack of regular "exercise" since it was 6 years old and only 48 hours on the generator. I could likely be it was not fine-tuned for adjustment after that. The service manual describes the process.

Does it sound right to you that where the manual dicusses the throttle stop screw it says with the generator warmed up and with no load, you "Adjust the stop screw to to obtain a frequency of 44 to 46 Hz on 60 Hz gensets." Since that is not normal Hz range, does that mean the governor speeds up the generator to 60 Hz under load as needed? I ask because earlier in service manual in the section on governor linkage and speed adjustment screw it states "With the unit operating at no-load, adjust the speed adjustment screw on the governor linkage to obtain 62.5 +/- 0.5 Hz, at between 120 and 126 volts on 60 Hz units."

The latter sounds correct and contradictory to the former, unless the governor is expected to kick up the "idle" speed when it senses the need.


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[Burfield]

Sounds right since the no load idle is basically a stand by mode. The stop screw is not the same as the speed adjustment. Your right that the governor should kick the RPM up to meet the demand, how it’s linked on the older units I don’t know. The 2015 model I have is solid state and not user adjustable.
The caution is not to set the idle speed too high under no load conditions.
Had a 1970 AS and it came with an Onan built into a side compartment. It’s a good generator

[rowiebowie]

Thanks to all who posted advice.

I went back and carefully re-read the Service Manual and successfully tackled the job yesterday. My generator had the old "Throttle Stop Screw, Governor Speed Screw, & Governor Sensitivity Screw" setup.

Summary:

My genny had the carburetor replaced just prior to my purchase last October, and I believe they were lax in setting proper speed adjustment as (unknown to me) it was operating at low rpms and output was only 117 volts/ 54 Hz at rest and dropped to 106 volts / 53 Hz under load.

The adjustment procedure in the Service Manual was pretty straight forward, but took a quite a while as I adjusted in fairly small increments, added load, tested output, and repeated many multiple times. Ultimately, I had to adjust the Governor Sensitivity Screw 4-5 full turns (in 1/2 turn increments) since after making the other adjustments, the governor began to "hunt" excessively.

In the end, I was within Volts/Hz tolerance under no-load (126 volts/ 63 Hz) and under A/C load (117 volts/ 60 Hz). The governor now runs smoothly under load.

Final Point:

Prior to mine, I never read a post on generator output. Sure there are many posts on running issues, ability to start a/c's, noise, etc. But my generator was running acceptably (or so I thought). It started my a/c, ran smoothly, and gave no indication it was putting out marginal or potentially damaging power.

I only tested it as an after-thought to installing my new a/c when checking to make sure I was getting adequate current through my 20A household plug. I found the low output using my Progressive Industries EMS-PT30X plugged into the galley outlet.

How many more generators out there get serviced and never adjusted to proper output levels? Probably more than we think and worth testing, in my opinion.


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[r carl]

Originally Posted by Burfield

I have a Koehler generator and it automatically adjusts the RPM Based on load. Surprised if the Onan does not have this feature. Do not normally want to mess with the throttle screw, over speed will damage the generator. Sound like your governor is not linked to the load demand. Think I would call Onan.

I think just inverter generators do that.

[Burfield]

Great you were able to adjust all that. As far as I know the new ones have limited user adjustments. Have to buy new electronics. Sometimes old school is more friendly to repair.

[rowiebowie]

Originally Posted by Burfield

Great you were able to adjust all that. As far as I know the new ones have limited user adjustments. Have to buy new electronics. Sometimes old school is more friendly to repair.

The main reason I tackled the job this week is 5 days of intermittent rain and full clouds keeping temps in the high 70's (instead of 90's). Still, plenty warm when reaching deep into a hot generator case to the governor adjustment screws.

Glad I got it done when I did. After 13 inches of rain in the past five days, mosquitoes are coming out and temperatures return to the sunny 90's tomorrow.

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