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Old 06-27-2013, 04:01 PM   #1
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Generator noise

A comment in another thread prompts me to ask about generator noise. My generator seems to be very noisy. Onan claims it is the quietest in its category, but it seems quite loud ---quite a bit louder than the quiet diesel I had previously.. The muffler and connections all are tight, but I would hate to run this thing in a crowded campsite even if quiet hours are not in effect. Am I expecting too much, or do others also find their generator to be noisy?
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Old 06-27-2013, 05:12 PM   #2
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A comment in another thread prompts me to ask about generator noise. My generator seems to be very noisy. Onan claims it is the quietest in its category, but it seems quite loud ---quite a bit louder than the quiet diesel I had previously.. The muffler and connections all are tight, but I would hate to run this thing in a crowded campsite even if quiet hours are not in effect. Am I expecting too much, or do others also find their generator to be noisy?
Loud from inside, or loud from outside? My generator sounds louder from inside the RV than it does from outside, due to the fact that the generator is tucked up underneath and all the sound that doesn't get out the sides goes up through the floor.

From outside, my generator is about the same decibels as the 3.0-liter diesel engine when the engine's idling, and quieter than the rooftop air conditioner.
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Old 06-27-2013, 05:32 PM   #3
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Billshop,
1. What steps have you taken to try to objectively quantify/evaluate the noise produced by your generator?
2. What kind of RV was the quiet diesel generator you're describing installed in.
3. Are there differences in how the generator is installed between the two RVs?

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Old 06-27-2013, 07:13 PM   #4
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From outside I find the generator to be way louder than the Sprinter's engine or A/C unit. Inside the A/C unit is louder than the generator. I think that's just the way it is. (Hence the Honda EU3000iS I mentioned in what I believe was the other thread you referenced.) I started a thread a while back about making the Onan quieter. http://www.airforums.com/forums/f240...ter-94379.html
I never followed through with the muffler experiment I mentioned there, but if you venture in that direction I'd love to "hear" your results. Good luck!
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Old 06-27-2013, 08:13 PM   #5
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russ240,
Your linked thread has some interesting information and is worth the read for anyone.

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Old 06-28-2013, 03:30 AM   #6
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From outside I find the generator to be way louder than the Sprinter's engine or A/C unit. Inside the A/C unit is louder than the generator. I think that's just the way it is.
Odd that we have exactly opposite perceptions. But then again, all sound-producing equipment has a "peak" frequency. The generator, air conditioner, and engine all have different peak frequencies, and it's possible that your hearing is more sensitive at the generator's peak frequency than my hearing is. I do have some work-related hearing loss, but not enough to qualify as a disability. My hearing is more sensitive at the air conditioner's peak frequency.

Because of hearing sensitivity, we could both listen to exactly the same unit and have different perceptions of the noise level.
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Old 06-28-2013, 05:17 AM   #7
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I can hear my generator across the parking lot. .It certainly is louder than the engine and/or the air conditioner when outside. When inside, the air conditioner is louder. The diesel generator I mentioned as comparison was a 10kw on a 43foot class A, and I certainly don't expect the smaller Onan to be as quiet as that. But nevertheless it seems it should not be that much nosier.
The noise seems to be more of a rattle than normal exhaust .

I think my next step would be to ask an Onan dealer to determine if my noisy generator is within the specs that Onan states. Thanks for the info. It was helpful to get the different views, and the link to prior discussions was most helpful..... Thanks all
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Old 06-28-2013, 05:19 AM   #8
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BTW... I have a significant hearing loss, so even normal conversations are difficult for me to hear.
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Old 06-28-2013, 05:42 AM   #9
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The noise seems to be more of a rattle than normal exhaust.
Unless something is loose, it shouldn't rattle at all. Last time you checked the oil, did you get the enclosure door shut tight? If the enclosure door is open, the generator will sound louder, and the door will rattle.
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Old 06-28-2013, 06:13 AM   #10
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Quote:
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I can hear my generator across the parking lot. .It certainly is louder than the engine and/or the air conditioner when outside. When inside, the air conditioner is louder. The diesel generator I mentioned as comparison was a 10kw on a 43foot class A, and I certainly don't expect the smaller Onan to be as quiet as that. But nevertheless it seems it should not be that much nosier.
The noise seems to be more of a rattle than normal exhaust .

I think my next step would be to ask an Onan dealer to determine if my noisy generator is within the specs that Onan states. Thanks for the info. It was helpful to get the different views, and the link to prior discussions was most helpful..... Thanks all
My generator has been very noisy since new (Apr 2013) as well. My wife says it shakes the house when I run it while parked in the driveway. A month ago (May 2013), the exhaust pipe fell (shook) off the generator while parked in a parking lot, and the generator was just as loud without the pipe/muffler as with it on! I had the oil level checked while I had the AS back at the dealer and it was ok. So I'm thinking that the generator just needs a good muffler.
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Old 06-28-2013, 10:16 AM   #11
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The heat shield on my generator's exhaust lost a couple of bolts and the vibration noise it created was very loud.

I agree w/ Protagonist's perception re: A/C being louder inside than the generator but may be 70 yr old ears coupled w/ tinnitus. Outside tho, I'd say it's a little louder than the 3.0L diesel @ idle.
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Old 06-28-2013, 10:18 AM   #12
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I have the same problem. Had the experience this morning with other RVs are around with either quiet built in gennys and the portable quiet Hondas and Yamahas. I had it on for 2 minutes to charge the inadequate batteries (longer story) and had to turn it off and start the engine because I was embarrassed from the noise. They put a straight pipe on the thing. I am going first thing next week to a custom muffler shop and finally take care of this. I'll let you know how it goes.
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Old 06-28-2013, 01:50 PM   #13
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[QUOTE="Ripple;1319338"They put a straight pipe on the thing. I am going first thing next week to a custom muffler shop and finally take care of this. I'll let you know how it goes.[/QUOTE]

So I just went to a muffler shop, and they told me that as far as generators go that can run AC, it is on the quiet side and that it's not going to be any quieter by adding a muffler. I'm not too sure if this is entirely correct so I'm looking forward to what other shops tell you.
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Old 06-28-2013, 02:38 PM   #14
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What generator is installed on the Interstates? Does anyone have a drawing of the installation of the generator?

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Old 06-28-2013, 03:21 PM   #15
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What generator is installed on the Interstates? Does anyone have a drawing of the installation of the generator?

Steve
Onan 2.5kW propane generator. Don't recall the exact model number. It's mounted underneath, between the spare tire and rear axle, but I don't have drawings. And I can't get far enough under the unit to get clear pictures.
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Old 06-28-2013, 05:31 PM   #16
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Protagonist,
I did some looking (pulled up the 2013 AS Interstate Owner's Manual and Parts Diagram) and the generator is a Cummins Onan 2.5HGJBB (see attached .pdf). Unless there is something loose on the generator that is causing a rattling sound, or an exhaust leak/muffler defect or something of the sort I'd say that this generator is simply going to be moderately noisy as perceived in comparison to a diesel/gas/propane generator in a larger motor home with lots more sound isolation. Let's face it, it's a single cylinder, air cooled generator with some sound dealing material in the cabinet/enclosure and the enclosure has some acoustical considerations in its design. However, there's no way that you can have a small lawn mower type engine with a fair sized muffler running and installed in a van and not have a fair amount of noise and some low frequency vibration that may be perceived as noise. Both noise and vibration contribute to some level of fatigue and exasperation, even if it's subliminal.

I spent most of my working career as an aviation electronics engineer for a general aviation manufacturer. I also have a good bit of experience flying these airplanes and instructing in them along with working as a design team member in acoustical improvements and it's darn difficult to take noisy machinery in a small enclosed vehicle and make it quiet. The more you can separate the noise from the listener in distance and by using acoustical absorption, detuning, etc. the less noise the listener will here or perceive.

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Attached Files
File Type: pdf Cummins_Onan_Generators.pdf (1.44 MB, 92 views)
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Old 06-28-2013, 05:45 PM   #17
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Billshop,
Something else to consider is to judiciously add some sound adsorptive material like Dynamat to see if you can damp some of that noise. You don't want to compromise cooling. Also, a longer, larger diameter exhaust pipe with a greater wall thickness might help as long as you do it in such a way as to avoid carbon monoxide problems.

Also, consider that any modification you make to your Interstate might void the AS or Onan warranties.

Steve
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Old 06-28-2013, 07:05 PM   #18
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Also, a longer, larger diameter exhaust pipe with a greater wall thickness might help as long as you do it in such a way as to avoid carbon monoxide problems.
It's already got a longer exhaust pipe than the Onan standard pipe, since it has to extend beyond the walls of the enclosure to the driver's side of the Interstate behind the rear wheels. Would there be any particular problem with replacing part of that longer pipe with a muffler?
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Old 06-28-2013, 10:29 PM   #19
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It's already got a longer exhaust pipe than the Onan standard pipe, since it has to extend beyond the walls of the enclosure to the driver's side of the Interstate behind the rear wheels. Would there be any particular problem with replacing part of that longer pipe with a muffler?
Protagonist,
I am a little concerned that you might have too much back pressure in the exhaust with two mufflers inline. Also, there might be a warranty voiding problem.

I'd wonder if there is a resonator that could be installed inline that wouldn't increase back pressure or at least very much. Mufflers tend to attenuate (reduce/absorb) a fairly wide spectrum of sound. Resonators are tuned to a certain resonate frequency and only cancel that frequency (and maybe a couple of harmonic frequencies an octave or two above the fundamental/resonate frequency). Many SUVs have resonators following the primary muffler where the pickup of the same basic vehicle will have the muffler only. I did a little bit of searching before submitting this post. Take a look at this.

Also, a more personal question. I've always suspected that it's better to be a protagonist rather than an antagonist, but I'm not sure. Do you have an opinion on this?

Steve
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Old 06-29-2013, 03:03 AM   #20
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Also, a more personal question. I've always suspected that it's better to be a protagonist rather than an antagonist, but I'm not sure. Do you have an opinion on this?
I have opinions on everything. Ask anyone; they'll confirm it.

But the username Protagonist has nothing to do with my personality. Before I bought my Airstream, my original plan was to buy a live-aboard boat when I retire, and travel America's Great Loop. Right up until foot surgery left me with ankles that don't bend the way they should, and I abandoned the idea of living aboard something that never stops moving even when you park it.

I was strongly advised to select a boat name with at least a modicum of dignity, and to avoid a pun in the name at all costs, because trying to explain the joke on the radio when talking to the Coast Guard gets old really quick. And, live-aboard boaters are known more by their boat names than their own names.

Protagonist was the only halfway decent boat name I could come up with that wasn't being used by ANYONE, so I'd never be mistaken for anyone else.

When I switched from full-time boating to part-time RVing as my retirement plan, I decided that I'd keep the name and use it on the Forums, because while it's a good name for a boat, it's too pretentious as a name for a dinky little class B motorhome.

And now, back to Onan generators in Interstates…
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