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Old 07-09-2020, 12:32 AM   #1
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THOR #12189
External Generator Noise

Has anyone implemented a muffler on an Onan 4kw gas generator?
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Old 07-09-2020, 12:53 AM   #2
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Get a Genturi...
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Old 07-09-2020, 06:44 AM   #3
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Originally Posted by The_Breeze View Post
Has anyone implemented a muffler on an Onan 4kw gas generator?
Are you wanting to quiet it down some? or get the exhaust out from under the slide?
If it's the later, the Genturi Bod mentioned will do the job.
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Old 07-09-2020, 03:44 PM   #4
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I did a muffler experiment. I used a beautifully designed polaris muffler.

The experiment is in my signature thread somewhere.
Leaving the onan muffler in place, an additional muffler had no affect. No affect straight on, less than 2 decibel at a 45 angle.
The muffler onan uses is actually very good at muffling.
The loud sound isn't from the exhaust it's from the miserable cast metal fan they use on the flywheel.

After some extensive-ish research I found a flywheel for 80 bucks I can buy, mill off the archaic miserable fan and then install an electric fan(I mean, if the damn generator is working the fan will be working, if the generator isn't, the fan won't).
Or
I've found Styrofoam board used as sound baffles will drop a bunch of staccato and mid range decibels off the fan. It leaves the bass. The noise is still there it just assaults less like a vacuum cleaner and more like a drumming.

But while building the baffle system, which is pretty easy:

I have since become convinced I can add a second alternator and run my v10 instead of the generator. It's quieter and my v10 uses just at/over three fifths of a gallon an hour, about what the onan uses.

So, for the investment in a second alternator(I already have a Biggish inverter and it stacks to go from 3k to 6k easily) I can sell the onan to recoup the alternator cost and wind up with a rather big storage area in the back, and a quiet smooth running v10 generating all of my elctric

I'm convinced generators are added to motorhomes because they're expected.
Since the advent of pure sine wave inverters a generator is kinda like a snapping turtle as a pet.
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Old 07-09-2020, 04:07 PM   #5
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External Generator Noise

I find the generator in my Magnitude SV34 not to be very noisy at all. It’s located more toward the front along with the exhaust exit so the noise is minimal in the bedroom. Not sure if the diesel version uses a different exhaust and cooling system than the gas versions.

If you are traveling in hot temps and humidity, I think a generator is a must to be able to run A/C. We have had a week of low to mid-90’s in PA so A/C is a must.

If you camp in places that don’t require A/C, then the generator becomes more of a luxury than a necessity. Given all the places we go, I want the generator.

If you want or need A/C when there isn’t shore power available, I think the generator is a must. By the time you add an Inverter large enough to run A/C, the batteries required and solar (or even an extra alternator) there is no net loss in weight.... and probably a weight gain.... if wanting to ditch a generator. And while the cost may be a wash if you sell the generator, the work involved would not be worth it in my opinion.
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Old 07-09-2020, 04:28 PM   #6
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I find the generator in my Magnitude SV34 not to be very noisy at all. Itís located more toward the front along with the exhaust exit so the noise is minimal in the bedroom.

If you are traveling in hot temps and humidity, I think a generator is a must to be able to run A/C. We have had a week of low to mid-90ís in PA so A/C is a must.

If you camp in places that donít require A/C, then the generator becomes more of a luxury than a necessity. Given all the places we go, I want the generator.

If you want or need A/C when there isnít shore power available, I think the generator is a must. By the time you add an Inverter large enough to run A/C, the batteries required and solar (or even an extra alternator) there is no net loss in weight.... and probably a weight gain.... if wanting to ditch a generator. And while the cost may be a wash if you sell the generator, the work involved would not be worth it in my opinion.
I agree with Judge, I have the XG32 Omni and the diesel generator is quiet. I did not find the generator in my previuos 31L all that noisy.
If you need to run the A/C you will want that generator.
Adding an extra alternator, inverters and batteries just to get rid of the generator just does not make weight and financial since.
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Old 07-09-2020, 04:43 PM   #7
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Originally Posted by ducksface View Post
Since the advent of pure sine wave inverters a generator is kinda like a snapping turtle as a pet.
I've had snapping turtles as pets: they don't bark, and they don't leave crap in the yard!
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Old 07-09-2020, 04:45 PM   #8
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I'm staying in a NF. I got a neighbor the other day so I walked down toward their site to see how loud the generator might be. There really wasn't anything I could do about it except look for ways to quiet it down. Hence , the question. Maybe the wind was blowing in just the right direction. I've done it before and either could hardly hear it or didn't hear it at all.

I'll look deeper into the Genturi Bob mentions and backed by KW. It's required at some events where space can be tight.

Thanks for the ideas. I like Duck's insulation idea to quiet things down inside too.
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Old 07-09-2020, 04:48 PM   #9
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I've had snapping turtles as pets: they don't bark, and they don't leave crap in the yard!
And they keep unwanted neighbors at bay
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Old 07-09-2020, 05:18 PM   #10
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I can run my ac for an hour right now with the v10 running and the generator off.
I need more battery as reserve and more alternator to do it for very long. One alternator upgrade the first time the engine bay needs accessed for taking off pulleys type of work, add the same batteries many here already have so no added weight there.... So it's a 67 pound inverter I already have.....
It must be a thing because Thor offers exactly this on some new models as an option.

Weight doesn't begin to be a factor with us.
I'm not one of the:
'I put our mattress in our towed vehicle because we weighed everything loose and luckily the mattress was exactly 30lbs and we were under 30lbs on tow weight and over by 30 lbs on rv weight. It's a hassle every night, but boy it's worth the peace of mind.'
Guys.

It's about one less perturbance. Generator posts are probably in the top five of hate and discontent posts on this forum. I have no generator issues.

My post was an alternative. I try to offer one anytime I offer a standard cure.
That's all it is. An alternative for the flockless.

My rv is a kit. I'll make it mine and not compromise due to the norm.

I appreciate counter points and often change my mind because of them.
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Old 07-09-2020, 05:28 PM   #11
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Originally Posted by The_Breeze View Post
And they keep unwanted neighbors at bay
Only when they get growed-up enough!
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Old 07-09-2020, 06:21 PM   #12
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The baffles go on the outside of the vehicle and really quiet the noise on the outside caused by the generator. Just get a couple of pieces of cardboard to experiment. You'll be surprised how much the ground will muffle the sound if you use the cardboard to find the sound origination and deflect it.
Its a fun experiment and just takes minutes.
Then you build the baffle you design out of Styrofoam that folds and either permamount it or make it fold up and you set it on the ground.
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Old 07-09-2020, 06:39 PM   #13
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Or...
You could just turn up the outside stereo, and drown it out in the first place!
Does anyone else like Inuit rap music?

Question: What is an Inuit's favorite Fleetwood Mac song?




Answer: "Tusk"!
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Old 07-09-2020, 07:19 PM   #14
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I've got a couple comments
I agree with duckface...almost.... generators are close to becoming old school. As Judge and other pointed out it's hard to run the ac off a battery. Fitrv.com did it in a little class B...put a huge lithium battery in place of the genny, and an oversized alternator to charge it. They can run the AC for some limited time on battery...like an hour if I recall.

I was tent camping once a long time ago at sun n fun. Across the road from where I was set up was a generator area. There was a guy diagonal across just a short ways that had some huge construction genny that would run all day. Well, there was a sign on the roadside made form two sheets of plywood hinged at the top, to stand like a sandwich board or a triangle pup tent. i moved the sign a few feet so it would be between that genny and my tent.... it was some distance away from the genny...maybe 20-40 feet I'd guess...and much further between it and me.... wow, what a difference it made!
I'd add this...a soft surface on the ground under the genny probably makes a difference too...grass better than pavement...etc...

I bought an onan exhaust resonator. Turns out it's just a straight through pipe with a perforated inner tube. Installed in the pipe after the genny's muffler. using a phone app dB meter I didn't find that it reduced the overall at all. i don't recall the numbers.... but what it did do was to "tune" the sound. It sounds just a wee bit less harsh. Not enough to justify the cost and effort really. Only the dB numbers before an after really aren't all that high even 20ft away....it's just that it's a harsh sound...so the resonator helped just a tiny bit.

Sometime after that, I found a muffler in Tractor Supply, that was roughly the same size and shape as the resonator, but it was a true muffler. I'll bet it would be better.

Attached photo shows the resonator.... also, the genturi that others mentioned probably does more to reduce the sound pressure....not a lot, but something. You can see part of my genturi attachment in the photo.
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Old 07-15-2020, 07:29 PM   #15
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I don’t get why their ”engineers” think it OK to have the generator exhaust under the slide. CO seeps in when wind is low.

I plan to get a genturi for that reason alone.

I’m very generator frugal. Don’t need much AC in Idaho and rarely camp where there is AC power. Got along 45 years with a 2kw Yamaha I’d run a few hours every few days. Never used AC on a half dozen of my RVs.

Now have an Onan 5500 and am using it a little more.
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Old 07-16-2020, 12:13 PM   #16
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Quote:
Originally Posted by The_Breeze View Post
Has anyone implemented a muffler on an Onan 4kw gas generator?
I’ve always understood you have to be careful if modifying the exhaust of an engine, ie restrict the air flow increases back pressure which could mess with the engine performance. Not sure how serious this could be, anyone care to expand on this?
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Old 07-16-2020, 12:22 PM   #17
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That's a good question.
I'm not sure if it applies to a stationary motor running at a fixed rpm level...

... unless the change affects that rpm level: which affects the power being generated...
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Old 07-16-2020, 05:15 PM   #18
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Originally Posted by Wilber View Post
Iíve always understood you have to be careful if modifying the exhaust of an engine, ie restrict the air flow increases back pressure which could mess with the engine performance. Not sure how serious this could be, anyone care to expand on this?
You are correct. Adding back-pressure restricts flow and will impact performance as well as fuel economy. The governor on the engine will generally make up for the loss in power by increasing the throttle to maintain the proper RPM while under load.
One other ďbadĒ thing about increasing back pressure is that it will cause the engine to run hotter - not just due to increased throttle settings, but because the engine gets part of its cooling through moving the heat out and away...
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Old 07-16-2020, 08:30 PM   #19
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You would think with the technology we have now they could improve the current generator lineup to be 10% (or more) quieter for little or no cost from the factory.

A little redesign the the Genny covers or shrouds, electic fan? Air vents design, Muffler? Some sound absorbing insulation?
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Old 07-16-2020, 08:39 PM   #20
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True...
But how much are you willing to pay for it?
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