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Old 06-28-2013, 04:21 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, 06:31 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.

Steve
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Old 06-28-2013, 06:45 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, 08:05 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, 11:29 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, 04:03 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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Old 06-29-2013, 07:44 AM   #21
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Protagonist,
Thanks for telling me about the username. I am always curious about the choice of names and words as I am a kind of wordy person (some might say that I blab too much). But I am always curious about word choice, derivation, etymology, how words morph over time...all that geeky stuff.

I also once met a man who named his airplane Panacea. When I asked him about his choice of names, he responded that I was one of the first persons to ask about the details of the name selection over several years of ownership. He also owned a boat with the same name and he felt no conflict because one vessel was nautical while the other was aeronautical in nature!

All my best,

Steve
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Old 06-29-2013, 08:39 AM   #22
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As some of you know, I have an Onan Microquiet 4000 genset "inboard" of my 2002 ASCL 31' (mounted under the curb side twin bed in the storage compartment). The exhaust note is VERY minimal, like rapidly puffing air, and is not annoying even within a couple of feet.

The engine mechanical and intake/cooling air noise is another matter though. It is heavily muted (normal conversation is no problem) when the curb side storage door is closed due to the door's insulation and the very convoluted air draw from under the frame; but when the storage door is open it roars and is not pleasant anywhere at curb side. Inside, the twin bed mattress and the 3/4" plywood containment enclosure along with the bed under storage compartment enclosure mutes 95% of the noise.

When the genset is running I'm only cognizant of it if I'm consciously thinking about it.
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Old 06-29-2013, 11:44 AM   #23
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For noise reduction we have attached larger flex stainless exhaust, at least 1/2 diameter larger and ran over 10 feet. No problem with back pressure. Next, we wrapped in Evil As-bestos for noise and heat reduction.

Now you could use the high temp options for wrap.

Use muffler hangers for support.

If you want full support, sleeve with pipe and paint...it use aluminum pipe
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Old 06-29-2013, 12:00 PM   #24
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For noise reduction we have attached larger flex stainless exhaust, at least 1/2 diameter larger and ran over 10 feet. No problem with back pressure. Next, we wrapped in Evil As-bestos for noise and heat reduction.

Now you could use the high temp options for wrap.

Use muffler hangers for support.

If you want full support, sleeve with pipe and paint...it use aluminum pipe
Generator noise is caused by the hot exhaust expanding, as it's released.

Cooling the exhaust gas, will quiet the system.

Attach an extension to the exhaust pipe, and you will be amazed how many DB you can reduce the noise by.

Use an adequate size pipe or flexible tubing of 10 feet or more. It should be the same size or a little larger than the exhaust pipe.

Some do it so well that the only noise you really hear is from the generator guts.

Andy
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Old 06-29-2013, 02:29 PM   #25
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An onan resonator is available. My local AS dealer has one on the shelf. JD Sanders RV. Also there is the Venturi? Which is attached to the exhaust and goes up along side the vehicle to exit the fumes and some noise away from ground level. Genturi? This s used after stopping for the day. Jim
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Old 06-29-2013, 06:19 PM   #26
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Generator noise is caused by the hot exhaust expanding, as it's released.

Cooling the exhaust gas, will quiet the system.

Attach an extension to the exhaust pipe, and you will be amazed how many DB you can reduce the noise by.

Use an adequate size pipe or flexible tubing of 10 feet or more. It should be the same size or a little larger than the exhaust pipe.

Some do it so well that the only noise you really hear is from the generator guts.

Andy
Hello Andy,
Can your shop weld in the resonator noted above for me? I'm also interested in solar panel replacement and addition. Your shop is not too far from me, in fact, you're right down the street from where I bought my Interstate (Southwest Coaches). Thanks in advance.
David
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Old 08-05-2017, 04:28 PM   #27
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I modified the generator's mounts and did a little insulating today and was able to get a 4.5 decibel reduction inside the van and maintain the reduced vibration level I had previously accomplished. Pretty good outcome. Here are the details. Wife and I sat int he back today with the gen running and had a normal conversation.

The iPhone Apps are not that reliable for decibel readings, but the delta should be relatively close.
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Old 08-05-2017, 08:28 PM   #28
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Thanks for posting the details - this mod is now on my ToDo list.
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