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Old 06-20-2018, 09:00 AM   #1
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Internally Mounted Generators- Sound Deadening?

I'm in the process of mounting an on board generator underneath the bus.

I scavenged an OTR truck apu, which provided me with a yanmar diesel engine w/ alternator and a sincro 5.2kva generator head. I combined all of that with a variety of other parts and now have a 4kw diesel generator. It's liquid cooled, belt driven, and has a 12v/40amp alternator. Perfect for my uses. Not overly loud either when muffled and the air cleaner installed.

Those of you that have mounted a genny under your bus, what have you used for sound deadening/heat blocking. I was looking at dynamat, but I'm not sure if I'm willing to spend that kinds $$ on something that I think is marginal. Anyone use anything cheaper/suggestions on it? It's going to be enclosed on the 3 interior sides with the radiator and fans facing the exterior. I'm keeping the bottom open to supply fresh air.

I was thinking of using some sort of mineral wool insulation and heat reflective mat between the genny and the floor. And then heat reflective mat on the sides.

Let me know what you've used and you're opinions on it.
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Old 06-20-2018, 11:16 AM   #2
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Quote:
Originally Posted by Booyah45828 View Post
I'm in the process of mounting an on board generator underneath the bus.

I scavenged an OTR truck apu, which provided me with a yanmar diesel engine w/ alternator and a sincro 5.2kva generator head. I combined all of that with a variety of other parts and now have a 4kw diesel generator. It's liquid cooled, belt driven, and has a 12v/40amp alternator. Perfect for my uses. Not overly loud either when muffled and the air cleaner installed.

Those of you that have mounted a genny under your bus, what have you used for sound deadening/heat blocking. I was looking at dynamat, but I'm not sure if I'm willing to spend that kinds $$ on something that I think is marginal. Anyone use anything cheaper/suggestions on it? It's going to be enclosed on the 3 interior sides with the radiator and fans facing the exterior. I'm keeping the bottom open to supply fresh air.

I was thinking of using some sort of mineral wool insulation and heat reflective mat between the genny and the floor. And then heat reflective mat on the sides.

Let me know what you've used and you're opinions on it.
I have some foam floor tiles that I am planning to use around the generator between it and the chassis. The vents will be on a side away from the chassis and or the bottom. Someone else said they used some kind of isolator in addition to similar garage floor foam tiles. Perhaps a search will reveal the explanation?
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Old 06-20-2018, 01:18 PM   #3
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insulation and sound attenuation

imagine a box around your gen set. that box has thousands of 1/8 holes in it.
Now place fiberglass insulation around the box..no paper just fiberglass. Now put a second box around the outside of this. the holes allow sound pressure into the fiber area that calms the noise down.

use rock wool, instead of fiberglass -- does not absorb water or any fluids really and is non flamable. If that gen set goes off for some reason this will help contain fire. watch air pathways The fan air flow may be used to air cool other parts of the system. Try to see how this was originally installed so as to evaluate air flow.

use as system that isolates gen set from bus by rubber mounts. These are usually best under compression... other words weight of the gen set sits on mounts, not hang from them. The looser you can float the parts the less vibration will transmit.

most engines, the air intake makes more noise than the exhaust. Same for piston type air compressors.

hope this helps

william
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Old 06-20-2018, 04:16 PM   #4
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Quote:
Originally Posted by 2martins View Post
I have some foam floor tiles that I am planning to use around the generator between it and the chassis. The vents will be on a side away from the chassis and or the bottom. Someone else said they used some kind of isolator in addition to similar garage floor foam tiles. Perhaps a search will reveal the explanation?
How thick are the panels, and what kind of density do you think they are?

Here are some other posts that I found, I was just hoping for a more in depth, this is what I've tried and it does/doesn't work thread.

http://www.skoolie.net/forums/f10/in...ator-1681.html

http://www.skoolie.net/forums/f13/ge...ing-22189.html

http://www.skoolie.net/forums/f13/in...area-5978.html
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Old 06-20-2018, 04:28 PM   #5
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Quote:
Originally Posted by magnakansas View Post
imagine a box around your gen set. that box has thousands of 1/8 holes in it.
Now place fiberglass insulation around the box..no paper just fiberglass. Now put a second box around the outside of this. the holes allow sound pressure into the fiber area that calms the noise down.

use rock wool, instead of fiberglass -- does not absorb water or any fluids really and is non flamable. If that gen set goes off for some reason this will help contain fire. watch air pathways The fan air flow may be used to air cool other parts of the system. Try to see how this was originally installed so as to evaluate air flow.

use as system that isolates gen set from bus by rubber mounts. These are usually best under compression... other words weight of the gen set sits on mounts, not hang from them. The looser you can float the parts the less vibration will transmit.

most engines, the air intake makes more noise than the exhaust. Same for piston type air compressors.

hope this helps

william
I was going to place rockwool aka mineral wool in between the "floor supports" underneath, then add a sheet of aluminum across the supports/wool, then heat mat over that.

Do you think I'd be better to drill holes into the aluminum to allow the sound to enter/disappate into the insulation? Would you still apply heat mat then with the holes drilled into it?

Genny will have 2 12" fans pulling air from in the compartment through the radiator, and vented to the exterior. The bottom will be open/grated so that is where the supply air will come from. The original APU had a similar setup, but it vented the hot air towards the driveshaft. That works in a semi because the space around the driveshaft is open at the top. In a bus however, I felt that this method would trap heat and any fumes underneath the floor between the skirting.

For vibrations, I've scavenged the mounts off the old apu, I also have shock absorber mounts that I've scavenged as well that I plan on using. Vibrations shouldn't be an issue.

I'll second the intake making more noise. During test running, I didn't install the air filter or muffler. After installing the intake it's noticeably quieter, I'll install the muffler when the whole works is mounted.
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Old 06-22-2018, 09:23 PM   #6
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Quote:
Originally Posted by Booyah45828 View Post
How thick are the panels, and what kind of density do you think they are?

Here are some other posts that I found, I was just hoping for a more in depth, this is what I've tried and it does/doesn't work thread.

http://www.skoolie.net/forums/f10/in...ator-1681.html

http://www.skoolie.net/forums/f13/ge...ing-22189.html

http://www.skoolie.net/forums/f13/in...area-5978.html
Mine are less than 1/2" thick and about 24" square. They lock together.
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Old 06-23-2018, 08:47 AM   #7
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holding the mineral wool ... helmholtz resonator

consider using harware cloth to hold the wool in place, that will leave about as much of the wool open for sound deadening as you can get.
Think about lining the sides of the box with the wool also...
I think it is good you are following guide lines of original cooling path.

that intake noise, look into something called a helmholtz resonator. also and this idea is out there man... I wonder if a set of noise canceling headphones could be hacked and connected to small amplifier speaker and with the speaker mounted in the gen set box, and use the sound waves of the electronics to kill some of the noise of the gen set.

william
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Old 06-23-2018, 05:44 PM   #8
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Yes on rock wool, that's what Blue Bird uses instead of fiberglass.
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