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Old 09-05-2014, 04:15 PM   #1
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Voltage surge

I started my Onan 6500 and a few minutes later turned on the front air conditioner on my 1988 345 motorhome. The selector switch was set to the Front Air Conditioner. I no sooner pushed the start then the air conditioner started and immediately stopped. I decided to check the AC voltage and saw that it was reading 157v. I turned of the generator and restarted it after a minute and got readings back in the Green fluctuating between 120-130v.

I have no idea what caused the surge. I feel sure it caused the air conditioner to quit. I then checked my other appliances and found that they were all not working. I don't know where to check for a master circuit breaker or fuse to restore my appliances.

I also am concerned that whatever caused the inverter to output such a high voltage might happen again. For now, the generator/inverter circuit is staying between 120v and 130v.

Any help, would be greatly appreciated.
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Old 09-05-2014, 04:25 PM   #2
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Engine RPM determines the voltage.
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Old 09-05-2014, 06:08 PM   #3
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r carl

I'm not sure I understand. I thought that the inverter regulate the AC voltage.
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Old 09-05-2014, 07:19 PM   #4
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Bay watcher, you are correct. In an inverter generator the output voltage and frequency is determined by the regulator circuits in the inverter. In the old conventional generators engine speed determined the frequency. That's why they had to run at high rpms. The generator part (probably an alternator and rectifier just like in your car) of an inverter generator puts out DC. The inverter converts that DC to AC and regulates the output voltage. The frequency is fixed by a timing circuit.

If all your appliances are off, check for a tripped breaker on your generator or a master breaker on your AC panel.

Al
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Old 09-05-2014, 07:56 PM   #5
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The Onan 6500 is not an inverter generator. It's voltage is controlled by the engine speed. Most likely something caused the governor to misbehave and overspeed, causing both the voltage and the frequency to go way out of specifications. This, as you have found, will cause damage on various pieces of equipment.

When plugged into grid power, will your AC and other things work?
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Old 09-05-2014, 08:22 PM   #6
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Oops. I keyed off the OPs using inverter. My mistake. Could easily have been an overspeed problem then.

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Old 09-05-2014, 11:39 PM   #7
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Thanks for replies

Hello idroba & Al.

From your comments, I believe that the generator is very likely the culprit. I've heard the engine speed change before, but this is the first time I've experienced an outage.

I'm seeing from your comments that my airstream doesn't have an inverter. So I downloaded a pdf for my generator rom the Cummins/Onan website. I see that the governor controls the consistency of the generator's output. It seems that is where my problem originated.

I don't know much about adjusting the governor, but if I need to I can read the manual and hopefully fumble my way through it.

It also appears from reading the manual that I might not have run the generator long enough to establish a stable voltage supply. I haven't used the generator often enough to realize that it takes some time for the engine to settle into a stable output.

I guess those are some of the growing pains for newbies.

I very much appreciate you taking the time to help me through this problem.

I hope that one day I'll be able to return the favor.
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Old 09-06-2014, 12:32 AM   #8
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I would not adjust the governor to start, but would take it apart as much as you can or dare while not adjusting the settings it now has. Then carefully lube it. It is 26 years old now, and not surprising that it might need some attention. Only if it seems to be moving smoothly but not running at the right speed should you get into the true adjustment of the governor mode. The "right speed" will be in the specs as a voltage output number, most likely. That will also give you the right frequency.

Also, as you mentioned, give the thing some time to settle down (warm up) before you put a load on it. The old onan's were a good generator, but not as nice as today's little inverter generators which do all their adjustments with electronics.

The Onan's used carbs, with mechanical governors to control the system. Good for the time, and pretty reliable, but a bit fussy.
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Old 09-11-2014, 07:50 AM   #9
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I found with my little Onan in the B190 that it helped to "step up" the load as much as possible. So, I would turn on the A/C in fan mode first, let that settle down for a minute or so, then switch to cooling mode.
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