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Old 02-03-2007, 08:48 PM   #1
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Instructions for quieting a Generator

Guys,

I just came across a site that has instructions on how to quiet your generator. It includes all of the stuff that you need to quiet down a Coleman generator (probably the loudest of them all), with a 10 HP B+S motor.

http://www.alpharubicon.com/altenergy/gensetquiet.htm

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Old 02-08-2007, 07:54 PM   #2
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Thats good stuff. I was think myself about getting a muffler for a motorcycle or a atv and adapt it to fit when I do get a generator.
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Old 02-09-2007, 02:45 PM   #3
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The guy, that wrote the article, said it quieted his Coleman (I think) generator, quieter than a Honda. Now, that's really something to brag about.

I'm also going to try it as soon as I get a gennie (I think I can pick up a used gennie for a very reasonable price).

Good luck on yours. If you get to convert yours before I do, let us know how well it works.
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Old 02-28-2007, 09:12 AM   #4
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I don't know if I said this anywhere on Skoolie.net, but I used a car muffler on a noisy genset maybe 7 years ago.
Basically added a $20 muffler similar to what this guy did. The car muffler is so large and has such a low internal resistance (relative to the genset exhaust pressure/volume) that it just absorbs the noise.
I too used flex exhaust tubing to allow the genset to move and not stress the muffler connection.

The muffler can be permanently mounted to the frame, maybe using a heat shield between the gennie and muffler, and a cage to protect the muffler from damage, and the folks from the hot muffler.

BTW, you can wrap the muffler, exhaust tubing etc. with a high-temp insulation, and that may have the benefit of increasing the efficiency of the genset....don't know for sure, but they do that a LOT with high-performance car exhausts, and it does help THEM.
The insulation would help absorb even more ambient noise from the genset mechanicals.
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Old 02-28-2007, 08:03 PM   #5
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Ryan, what kind of genset did you do this with and did it make a drastic difference in noise?

-Richard
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Old 03-01-2007, 10:15 AM   #6
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It helped a LOT with noise.....the idea was to set up a friend's house for possible Y2K problems (no problem, obviously), and the quieter, the better. If no one knows the unit was there, they're not likely to steal it.

It was an ancient but rarely run Sears Craftsman gennie, when my buddy got it used it had probably been run only once; the paint on the muffler was barely blistered!
I used a generic small car muffler he bought at Meineke, and a few exhaust ells/flex pipe/fittings. I hammered out a flange on a stub of exhaust pipe, pop-riveted that to the gennie muffler, and went from there.
The enclosure we made from 3/4 sheet ply, lined with rigid insulation, cut a few holes for ventilation, with a small fan screwed on there to keep stuff cool. The fan plugged directly into the gennie: if the gennie ran, the fan ran.
The relatively immense capacity of the car muffler easily absorbed the small engine exhaust noise. With the muffler designed to control 500+ CFM of exhaust, it barely slowed the 150(?) CFM of the gennie running flat out....no back pressure increase to speak of.

From about 15 feet away you could hear the mechanicals running (without the enclosure), from 40 feet you hardly heard a thing, IF you were listening for it....otherwise it was QUIET.

Y'now, they do something like this for Burning Man, I've seen it in photos. Build an enclosure, it absorbs some noise, reflects the remaining noise upwards.
Some also dig a hole and plant it below ground level so any noise not absorbed by the ground is radiated upward.
I remember seeing at a hobby show, a guy cut a 55 gallon drum in half crossways; he lined it with fibreglas, and rewelded the base back on it. Then he plumbed the exhaust from a model airplane engine into the drum. Used indoors, you heard the prop whistling, and the engine sucking in air through the intake, and the mechanical rattle of the ignition as it fired....that was about it.

BTW, I was watching TANK OVERHAUL on cable last night (DVR), and the M18 tank destroyer they worked on had a neat feature: the rear engine compartment hatch folded down, and when down, it acted like tracks to pull the engine (on rollers) out for changes or repairs. Doing something like this on a bus would make installation and maintenance a breeze. The compartment cover can also be the access tracks/ramp.
Mounting the gennie on a heavy plate, and having that plate on heavy rubber isolators will keep it quiet (absorb some mechanicals normally transmitted through the base of the gennie) as well. Some years ago I found out you can buy noise isolators tailored to specific frequencies, so if you know what freqs the gennie is putting out, you can absorb that completely.

I've written about noise and gennies somewhere else, can't remember where. Basically, noise is absorbed by changing it's frequency, or deflecting it away.
Heavy objects absorb the noise because it's natural frequency is too LOW to have a resonant reaction to the offending noise.
Other materials absorb the noise (insulation, for example) because it's energy gets lost in the random frequencies that the insulation is made of.

Some mufflers use a noise-cancelling principle, where they make the noise reflect back on itself; one interesting effect of this is in tuned exhausts like on 2-stroke engines. The noise is also used to extract the exhaust pulses, making the effective exhaust pressures (and horsepower losses) lower, even increasing extraction, WHILE STILL KILLING THE NOISE....horsepower GAINS are the point here.

Another trick is like most auto mufflers use: make as many 90 degree bends as possible, and pass the exhaust pulses through holes; it makes the pulses tend to cancel each other out. Those bends absorb energy.
This type of exhaust robs horsepower though, unless you use a REALLY big muffler to keep flow levels up. That's why back in the day I used an International Harvester truck muffler in my '68 Mustang: it fit the same, but the huge intake/exhaust pipes cut back pressures while still absorbing noise. Kinda like a Stealth Bomber......

Hope this answers the questions, and any more you may have.

Ryan
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Old 03-01-2007, 07:13 PM   #7
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The head mechanic at the bus garage where I work suggested to tie the exhaust into the bus' muffler. He said he saw a setup like this once and it was really quiet.
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Old 03-02-2007, 09:08 AM   #8
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the geni in that article is the exact unit that i have and don't use because it's too noisy.
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Old 03-03-2007, 02:59 AM   #9
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Hey guys,

I'm sorry I haven't go on recently. I'm not ignoring ya'll, I'm busy looking forr another job (too many hours in the present one)

Anyways, here I go:

Ryan, I really didn't want to take away from your post (I do remember seeing it and liked it), I just saw the article and thought it was neat. The biggest thing I liked about the article was the pics of the gennie and the mods. They also gave part numbers for the mod.

BTW, I wouldn't have even noticed the article if it wasn't for you making me aware of the idea (I really don't have too much of an imagination, or so says my ex)

Rick, the idea sounds great, using your bus muffler, but trying to connect to it would probably be a pain for me. I don't weld much and I would have to get a shop to do it for me. Could you imagine what I'd get from the techs there? Remember, I'm in Houston and they have even less of an imagination than I got
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Old 03-03-2007, 03:03 AM   #10
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Hey Jason,

I was wondering if you ever tried putting a muffler to your gennie? The reason I ask is because if the unit is still noisy, it probably wouldn't be worth modifying.
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Old 03-03-2007, 09:05 AM   #11
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Lets explore the idea of the gennie being tied to the bus muffler.

Would it actually work with out causing damage to a diesel or gas bus engine? Meaning when the exhaust is piped into the exhaust tubing in front of the muffler, theoretically it would have to fill the entire exhaust pipe before going through the bus muffller, wouldnt it?

And if it does, what effect would it have on the bus engine's valving, exhaust manifold, etc? If any.

That would be an easy way to connect a large muffler to the gennie. Especially on mine, where it would be a straight shot after one 90* bend.
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Old 03-03-2007, 09:14 PM   #12
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I think that might work ok. You'd rarely, if ever, have both running at the same time. I would fear a little that the exhaust pulses from the big diesel might overpower the gas engine if they were both running at the same time, but I really don't know. That also might be an awful lot of backpressure for that little engine even when you weren't running the diesel engine. Buses have a lot of pipe! It might work better to tie in behind the muffler. I know you lose the muffling properties a little, but a long, big pipe would probably do wonders. It would also move the exhaust note out the back, far away from the passenger compartment. My only question is this....if it would work so well, why don't the manufacturers of stick and staple RV's do it?
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Old 03-03-2007, 09:37 PM   #13
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I suspect that some of the generator exhaust would come out the bus engine's air
intake. Piston engines have a phenomenon called valve overlap, where both the
intake valve and the exhaust valve are slightly open at the same time. It may not
happen every time the bus engine stops, but once is enough when it comes to
carbon monoxide finding its way inside.
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Old 03-03-2007, 09:39 PM   #14
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Yeah, I have no clue if tying it in would work. The mechanic who saw that install said that it was on a RE bus and the gennie was in the engine compartment (must have been a small one).
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Old 03-04-2007, 03:04 AM   #15
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But for those of us with a conventional, I think the threat of carbon monoxide coming in through the intake is far less than through an open window above the gennie's "normal" exhaust.
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Old 03-04-2007, 10:37 AM   #16
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No doubt. I just wanted to brag about my Internal Combustion Engine knowledge.
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Old 03-04-2007, 09:13 PM   #17
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here's my suggestion:

use your tax return, beg, borrow, steal the $$$ so you can afford to buy a honda eu series geni.

the eu2000 will run 15 hours at 1/4 load on a single gallon of fuel

it's incredibly quiet

and lightweight. Under 50 pounds

pure sin wave so you can run sensitive equipment

plus you can hook 2 of them together and double the output

if you don't have a geni yet, then you should definately buy the honda. you can get an el cheapo gas guzzling noisy geny for $500, or a honda for under $1K. The fuel you save alone makes the geni worth the investment.

I know I know...it takes all the fun out of trying to quiet a noisy geni. I can appreciate the project.

I don't care what muffler you put on your briggs motor, you cannot quiet the exhaust enough to come anywhere near the quiet eu series.

i did the math....

After about 500 hours you would be saving money with the honda verses the cheap geni.

475 hours the honda would burn about 32 gallons of gasoline @ $2.50 that equals

~$80 in fuel

475 hours for the briggs motor @ 0.5 gph (that's what mine uses) it would burn about 237 gallons of fuel equal to about

$593 in fuel.

total price to buy the honda and fuel = $1080

total price for the briggs motor and fuel = $1093

Certianly all things are not equal. the briggs geni does 220 volts, and 6K watts. The honda only has 110 volts and 2K watts. The equation also assumes the honda is only running about 1/4 load. I find it makes not much difference how much load i put on the briggs motor, it still gets about 2 hours per gallon of fuel. I did use my honda for most of 2 weeks straight i the middle of the desert running my jacuzzi, a small fridge, lots of lights, ect and averaged about 15 hours per gallon.

ok, i'll step off my soap box now....afterall, the original post didn't ask about quiet genie's...it was directed toward how to make a noisy geni quiet.
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Old 03-04-2007, 11:44 PM   #18
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Other Honda powered gennies, while slightly louder and slightly more thirsty, are good options as well. My bus has been powered for an entire weekend by an EN series. We ended up powering all the other campers around us with it because it was so quiet and 1 gennie running at full load is still cheaper than two running at half load in terms of fuel consumption. I think the 2500 watt EN can be had for about $700 though I haven't priced them recently.
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Old 03-05-2007, 12:06 AM   #19
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Gawd, I love my Honda EUs. One EU3000is for stationary/semi-stationary use and
one EU1000i for very portable use.

Expensive -- and worth it.
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Old 03-05-2007, 05:03 AM   #20
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if you are adventerous i've read about connecting eu's of different sizes ie: a 1000 watt and a 3000 watt geni together to make 4000 watts. The guy who made the post has connected multiple geni's of various sizes all at one time. Even cooler is that you don't need the fancy $150 honda connector to connect the geni's....an extention cord with a double male works just fine.
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