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Old 04-01-2018, 01:42 PM   #1
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Generator issue, low voltage?

Hi folks, Happy Easter!

2015 28DS with stock 30AMP with an Onan RV QG 4000 that is well maintained and exercised to guide specs and 179 hours.

Ran A/C for a bit on gen and A/C shut off. Gen starts, looks and sounds fine. Measuring a low 72.5VAC at the 'gen outlet'. (see attached)

A/C and 120VAC work as it should on shore.

Any thoughts before I dig into this?

And why does this gen not shut off anyway when not generating the correct VAC???
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Old 04-01-2018, 01:51 PM   #2
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Generally speaking generator output is a direct proportion to motor RPM. So start there. Possibly a regulator is bad, or you have a dead windings. Other than RPM your pretty much stuck sending it in for repair.
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Old 04-01-2018, 04:24 PM   #3
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the onan generators are supposed to run at a constant 2400 rpm and they have internal regulators to monitor / adjust voltage to meet demands. but yes, I thought they were supposed to shut off for certain conditions, such as low voltage. so it sure looks like something is wrong internally. i'd place a call to onan support to see if they can diagnose the issue. be prepared for them to tell you to take it to an onan repair facility. I took mine there and was quite impressed. there are independent service organizations and mobile services that support onan generators. hopefully it is a control board that can be replaced and not a mechanical issue.
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Old 04-01-2018, 06:52 PM   #4
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Thanks for your reples!

Engine is definitely runnning as it should. And tonight after everything cooled off I started it and measured 121.5VAC at the outlet where I would plug in 30AMP plug. Intermittent problem perhaps indeed voltage regulator. (onan part# 305-0851) should be under two yr warranty...

Will follow up
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Old 04-01-2018, 07:04 PM   #5
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just speculation. could the problem be in the wiring from the generator to the receptacle you are testing at. perhaps the generator is working just fine and there is a loose or burnt cable.
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Old 04-01-2018, 07:17 PM   #6
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just speculation. could the problem be in the wiring from the generator to the receptacle you are testing at. perhaps the generator is working just fine and there is a loose or burnt cable.
Mmm that would either give 0 or 120... not a constant 72V. Now that it is working again that'll be tough to test I guess. But to make sure tomorrow I will load the gen with the A/C till it craps out and measure the voltage at the gen as well as the receptacle.

Service/parts manual reads: (3. & 4. are more likely with less than 200hrs...)
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Old 04-02-2018, 07:41 AM   #7
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Mmm that would either give 0 or 120... not a constant 72V. Now that it is working again that'll be tough to test I guess. But to make sure tomorrow I will load the gen with the A/C till it craps out and measure the voltage at the gen as well as the receptacle.



Service/parts manual reads: (3. & 4. are more likely with less than 200hrs...)


These generators have a problem with defective brushes. That was the problem with mine.
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Old 04-02-2018, 10:15 AM   #8
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Double checked the AC line from gen to receptacle & reconnected all connections.
Tested it again. Started right away and runs great. Warmed up and added the AC (~1500W) and ran just fine. Added the microwave (~1600W) and continued to run fine. Let' see how it holds up...

Will install Hardwired Electrical Management Systems from Progressive this week to protect the RV against it's own generator. You should do this as soon as you purchase an RV BTW
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Old 04-03-2018, 08:05 AM   #9
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Thanks for your reples!

Engine is definitely runnning as it should. And tonight after everything cooled off I started it and measured 121.5VAC at the outlet where I would plug in 30AMP plug. Intermittent problem perhaps indeed voltage regulator. (onan part# 305-0851) should be under two yr warranty...

Will follow up
I believe you have a 3 year warranty on the generator. Our generator just lost its intake valve keeper and the had to find the pieces and fix that. All under warranty on our 2015 unit. Whew...

When they where in there, they had to drop the generator to shake out the pieces I think and they found some of the AC wiring connections were overheated. Guessing poor wiring nuts or something (they didn't show me pics how its wired). Might be something to check, pull the cover off that junction box on the side of the generator. I believe there is an undervoltage fault code, #13 that it would post if that was the case.
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Old 04-03-2018, 08:17 AM   #10
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to kansasfr3: what do you mean your generator lost its intake keeper? what type of generator? i'm wondering if your problem was similar to mine. we have an onan 5500 lp generator. the valve guide in the cylinder head worked loose and moved up where it interfered with the rocker arm. onan replaced the entire cylinder head assy under warranty. but what was more interesting is what the onan tech told me. he said they see this a couple of times a year. they cannot prove anything but they think it might be heat related, if the head gets hot it expands and lets the pressed in valve guide work loose. he said to open the compartment to ensure adequate ventilation.
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