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Old 07-22-2018, 03:06 PM   #1
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Generator not revving up for more power.

At first I thought my AC stopped working, but now I think it is the generator.

it no longer "revs" when idle (as it used to) and it does not idle UP when under load. It still supplies power (120v) but it seems like not enough to run the AC compressors.

I ran the microwave on some water for 3 minutes and the water was only slightly warm. So my guess it was not running at full voltage. The fan on the AC also does not increase when I go from LOW to HIGH. I also tested a portable heater and got the same thing... Fan speed does not increase when set to HIGH.

So my WILD guess is that this function of the generator is electrical and not mechanical? Maybe I need to replace the circuit board?

The generator does "react" when I put it under load... there is a slight change in sound, but it does not rev up.

does "circuit board" sound correct to you all?
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Old 07-22-2018, 07:19 PM   #2
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A bit of a wild guess here, but I think maybe your generator is designed to provide a constant speed in order to hold the frequency to 60 cycles per second.
That is usually 3600 RPM.

Now when your generator loads up and has to provide more power to it's limit, the circuitry in the electronics changes, and as it asks for more power to supply the load, what you think is faster speed is actually just more power up to the limit, then it will kick off.

The circuitry in the electronics changes voltages and currents inside the generator winding, and the fuel input to the generator senses that and it works harder to stay right on frequency, but sounds louder, and stays at the same RPM.
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Old 07-23-2018, 01:14 AM   #3
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It used to work fine and it DID rev WAY up. And it was obvious that it changed RPM. But since this problem, it stopped changing the RPM.
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Old 07-23-2018, 07:49 AM   #4
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My understanding is that LP gensets will vary RPM as needed, however the diesel gensets run a constant speed. I can still hear the when a heavier load is on the diesel.


Perhaps you need to get it to a shop that knows how to fix it right the first time. Perhaps he problem could be the control unit, poor mixing of LP, not enouigh LP pressure or something wrong with the coil of the gen. It's possible the problem could be mechanical or electrical.


For me that seems like a job for someone who knows these systems.
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Old 07-23-2018, 10:10 AM   #5
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It is a regular gas generator. Not LP or diesel. It for sure is supposed to rev up. I am just trying to confirm that this is regulated by the control board and not a mechanical thing. Somebody must have had a similar problem.
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Old 07-23-2018, 11:20 AM   #6
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According to the 2000 Adventurer brochure a 5000 or 6500 watt Onan Emerald generator was offered. That sound right? Do you have the 5000 or the 6500?

A search of the model number would surely find more information for it. I found this for an Emerald Plus 6500:

http://campkahler.com/files/onan/emerald6500.pdf

It says it runs at 1800 RPM. Not sure if that is the right model family though (flyer is for the "NHE" series).
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Old 07-23-2018, 11:59 AM   #7
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It is the 5000. Like I said, it was working but now it is only throwing minimal power. If I manually rev it up, I get more power. Enough to get the fans to blow on High.
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Old 07-23-2018, 01:36 PM   #8
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I pulled the voltage regulator out of it. I don't see any noticeable damage, but I assume it HAS to be this part that is broken. It is like $400 to replace it, so I hope I am right!
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Old 07-24-2018, 11:47 AM   #9
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Here is what my regulator looks like : https://photos.app.goo.gl/r2qnCRHRGbdDWXor8
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Old 07-28-2018, 05:50 PM   #10
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If your generator changes speed, then the most likely problem is with either the carburetor (fuel supply) or the governor. The generator is designed to run at a single speed in order to provide a constant 60 hertz frequency. As load is added, then the governor will open the throttle plate on the carburetor to maintain frequency. As load increases, the voltage "droops" and the voltage regulator will provide more exciter amperage to keep the Volts/Hertz ratio at the desired setting. Once the exciter is at its upper range, then voltage will drop, even while frequency is maintained.

Unless you checked voltage as load was added, you're just shooting in the dark. If you have the funds to Easter-egg a problem to its final solution, then I guess you're no worse off in the long run.

The single-speed generator will have a fixed speed, depending on the number of poles in the generator.
F=N X P/120 (F= frequency, N=speed, P = number of poles)
N = F X 120/P
So, a four-pole generator will run at 1,800 RPM

A two-pole generator will run at 3,600 RPM.
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Old 07-28-2018, 05:58 PM   #11
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“As load is added, then the governor will open the throttle plate on the carburetor to maintain frequency. “

I think this could be misconstrued as revving, depending on the listeners relative experience. It might be better to consider his predicament as no governor engagement when load is added. Now, what could cause that?
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Old 07-28-2018, 06:21 PM   #12
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Tommymsw;

I have owned 4 Onan gasoline generators and now a Onan Quiet Diesel Generator. My experience tells me that in principal all 5 have operated the same. I feel VI Romers is correct that the generators are controlled by a governor to produce 120V at 60 Cycles at a certain RPM. When the generator is asked to produce more power the regulator provides more fuel to keep the RPM steady. What sounds like the generator speeding up is the generator laboring harder to keep the voltage & frequency stable.

When the generator is asked to produce more than the generator is sized to produce. the breaker or breakers will trip on the generator to protect it from overload. When the load is decreased the governor will decrease the fuel supply to keep the generator from over revving and producing more than the 120V & 60 cycles it is supposed to produce. That sounds like the generator is reducing speed but it should still be running at the preset RPMS.

I have A/C Voltmeter plugged in to an outlet near my control panel that I monitor all the time when I walk past it. It helps me to monitor the generator voltage when it is running and also to monitor the campground pedestal for proper voltage when plugged into campground power. Believe it or not I have never found a voltage problem with any of my Onan generators but have found many lower voltage problems in campgrounds especially older ones. To me it sounds like you have a governor problem.

JMHO so take it for what it is worth to you. The regulator or governor could have the same function I am not sure on that.

Don
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Old 07-28-2018, 08:53 PM   #13
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Tommy what year make model do you have. There are inverter/generators on the market that do not rely on generator rpm for proper power supply. I think more information would help.
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Old 07-29-2018, 12:03 PM   #14
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27Winnie

Tommy: I had an issue with my Onan 4000 generator. I determined my diagnostic abilities were not sufficient to find the "exact" problem. You may want to do a search online for the nearest Cummins Onan repair facility. Onan is owned by Cummins. In the Seattle area they have a shop with two bays - one to repair Cummins diesel engines; another where two technicians work exclusively on Onan generators. In about 20 minutes the tech diagnosed my generator issues and repaired it. Cost about $90 for one hour work.
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Old 07-29-2018, 12:41 PM   #15
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I have an Onan Emerald 5000 generator model 5BGEFA26100P.

It used to work fine and I know what it did and sounded like when it was working. It would throttle up, you could watch the throttle move to give more gas. It would rev up and get louder. Also when there was ZERO load on it (before I turn the circuit breaker on), the engine would "rev" up and down, like when you rev a motorcycle. Up and down, up and down, over and over until I turned on the "on switch" to tell it to supply power.

One day it just stopped doing that. Now it just starts and runs at a constant speed. When I put load on it, the generator does make a sound change but not like it used to... it used to idle up. Now it sounds as though it is being pulled upon and struggles.

also, when I turn on the A/C, not only does the compressor not start, but there is little to no change in fan speed between LOW and HIGH. If I manually throttle up the generator, I can get the fan to run on high.

i took the voltage regulator out and tested it.

"With the meter on “Diode Check”, test between
connector terminal pairs 5-9,7-9,lO-9,ll-9,12-9,
10-5, 5-11, 5-12 and 5-3 (Figure 8-13). It is important
that the positive lead of the meter be connected to the first terminal of each pair. Replace the voltage
regulator if any reading indicates “short” or “open“,
except for pair 10-5, which should indicate “open”.
“Short” is indicated by zero or a number very nearly zero.
Meters of different make indicate “open” differently."

At each spot I get a (1) reading. I get (0) when I touch the probes together. From the 10-5 spot I still get (1). Even if I reverse the probes here I get (1). I am not 100% sure, but I think I am supposed to get a (0) from that spot?
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Old 07-29-2018, 01:48 PM   #16
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From my experience providing repair service on RV's, DryCreek is correct, something has gone wrong with the governor. You should be able to find a manual online, but the mechanical device reacts to engine load, opening the throttle to keep RPM. And there is adjustments.
You can check its operator by idling the gen with no load and look at the carb and where the throttle is sitting, should be on the idle stop screw or just off. When you apply a load, you should see the throttle open away from the stop.
If it doesn't, check that the governor rod can move manually opening the throttle.
If it does move and the RPMs are dropping, yes, you have engine problems, fuel or spark. New plugs and a fuel filter are a cheap test.
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Old 07-29-2018, 11:15 PM   #17
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Two things. First the rev up and down, that's carb problem most likely. SeaFoam should help that. Mix an ounce in a gallon of gas and feed it into the fuel line, in short order that should help. (2) There is a spring on the governor rod (end farthest from the carb) and probably under a cover. If the spring is dislodged or broken it will keep the throttle from working.
Hope this helps.
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Old 07-30-2018, 07:37 PM   #18
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The carburetor was just taken apart and cleaned and seafoam run through it. I fell like it would not have gunked up in a month while it has been running off and on the entire time.

i can manually pull the throttle open and closed again no problem. Spring seems fine. It HAS to be whatever the mechanism that pulls the throttle back. Engine runs fine, throttle seems to operate fine. It is just that the engine is no longer pulling the throttle back on it's own.

as far as the reving up and down, i thought that was a problem and I tried to fix it, until a professional looked at it and said "That is what it is supposed to do when it is not generating power".
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Old 07-30-2018, 11:21 PM   #19
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There is a shaft coming up from the generator engine hooked to the mechanism that pulls the throttle.They are hooked together at a 90 degree angle with a plastic clip. That was where my generator problem was. It's under a cover and on mine I had to pull the generator to get at it.
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Old 07-31-2018, 02:23 PM   #20
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It is entirely possible that you have a "two speed throttle" mechanism on your generator. When the electrical current load is reduced, the unit has an electric solenoid that either energizes or de-energizes for a slower engine speed to save fuel and cut noise. Then, the instant an electrical load is sensed, that solenoid pulls the throttle to make the engine go to full regulated speed, being controlled by the engine governor according to the load, and produce the proper current and Hz.

Having sold and serviced diesel and natural gas generators for several years, you may get someone to check for that solenoid on the throttle mechanism. Just a thought.

Best of luck, GT.
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