Quiet Generator Box Build

[OneLapper]

Todd,

I'm really enjoying this project of yours!  At my job I get to see all different types of generators installs.  Without doubt, the quietest are sets that are in a sound enclosure within another box. 

Remote mounting the mufflers and the intake filter, as well as the radiator really help, too. 

Keep up the great work! 

[86102A3]

Todd,
Thanks for sharing your build. I plan to also build my own enclosure as well.  What brand, size etc is your generator?
Also I thought I was reading my own ideas in your post about having a PLC on board, with the Cmore HMI, that is exactly what I am planning as well. I have been looking at the less expensive Click series PLC just to get me started. I am an industrial electrician and mostly deal with the field end of installs, so I will be on a bit of a learning curve for the programming end. Hopefully you can post some of your work on the PLC install, would like to see what you have planned.

Jeff

[Darkspeed]

Thanks Mark! Sounds like a cool job!

Thanks Jeff, it is a 8kw 1800rpm Quicksilver marine diesel.

I have never used the Click series before but I am sure it would work, I think it just has fewer features (most you may not need) and is memory address location based vs tag name based programming.

If you do some creative thinking the PLC can replace a lot of expensive systems in a bus.

I have a girl I hire to do voice over work who has an obscenely sexy voice and she records all of the touch screen alerts/messages as .wav files then I load them into the Cmore.

I have had companies refuse to let anyone else do plc work because the guys who operate the machines have developed an attachment to their touch screen lol.

[digesterman]

Count me in on that too Jeff,  reading this thread with great interest

[Darkspeed]

Making some modifications for adding a thermostatic remote oil cooler to give it every fighting chance to not overheat in a sealed box.

Thinking about doing inline cooling with the Dayton blower:   Baffle In > Blower > Enclosure Radiator > Oil Cooler > Engine Radiator > Baffle Out

The Dayton needs a minimum of 1" water static pressure or it will spin too fast and go into overload - it is designed that way

Tested the stainless exhaust on the intake side and it made a significant improvement.

When the better decibel meter ( A Weight ) shows up I will get some good numbers.

Going to try to drag everything below human hearing (20hz) and the left over I will convert to heat.

Mostly using decoupling layers and lead sheet as the damper materials ( like dynamat ) loose almost all of their damping ability at a heat higher than a car interior.

The best damper for higher heat is fiberglass resin mixed with small gauge lead shot and painted on to the metal panel - as long as you are below the melting point of the lead  

[Darkspeed]

I spent a lot of time watching the youtube videos , googling how-to's, talking to "car audio experts" just to get a feel for what the rv/bus/mobile home community does for generator sound control of the enclosure.... and I cant find anyone doing it to the known best practices. - with the possible exception of custom prevost -

The boat/marine folks seem to be doing it right but there is a disconnect to the on the road guys.. ( THAT I HAVE FOUND - NOT ALL IM SURE )

A lot of the on the road guys are making three mistakes  ( not judging or point fingers it is just an unqualified generalization )

#1 connecting the barrier layer directly to the enclosure  = screwing the lead or MLV to the plywood or to the aluminum bay = no decoupling layer

#2 relying solely on higher frequency absorption = foam / fiberglass / foil pads, panels = not absorbing anything below 8-4khz

#3 using dampening material full coverage as only solution = dynamat the whole box = no sound blocking only frequency reduction.

#4 big holes for venting the box - not really an error just the alternative to box cooling = inadvertently turning the box into a port tuned speaker.

We should be aiming for good isolation in the 80hz-500hz range for an 1800 rpm 3 cylinder

1800 rpm = 30 cycles per second ( 30hz ) and 3 cylinders (3 x 30 = 90hz) so we should see problems at those frequencies, plus the resonant cavity size of the cylinder, resonant length of the valve train components, etc... Most of this is going to be low frequency hot spots.

If we can drag all of the low frequency noise below 20hz we will no longer hear it.

Butyl dampening material is not going to be usable because it looses almost all of its properties at these temperatures.

MLV blocking material is not going to be usable because it looses almost all of its properties at these temperatures.

2 decoupled layers of 1/64 lead sheet is much more effective than one layer of 1/32 lead sheet.

-30dB layer @125hz (when attached to enclosure)= 1/8 EPDM decoupler layer > 1/64 lead sheet > 1/8 EPDM decoupler layer > 1/64 lead sheet > 1/8 EPDM decoupler layer.

This should reflect anything in the high range and give about 30dB reduction in the 125hz range, and up to -70dB in the 2khz+ range.

Internal box ( generator box )  -30dB layer on the outside of the enclosure
Outer box ( the bay ) -30dB layer on the inside of the enclosure
0.5 air gap between boxes ( a good -10B )
Generator on pneumatic isolators
Inner box on low durometer isolators.
Inside of inner box would have ceramic batting in corners to turn high frequency waves into heat.

If the generator was say 100dB @ 1 foot then the box should attenuate 70dB @ 1 foot minus anything transferred through the cooling hoses as longitudinal waves, for a total 30dB @ 1foot.

So in a perfect world you could have a 8kw Diesel running at full tilt and not hear it ( at 30 dB ) standing beside it, because a library is 40 dB.

This would take 155# of lead sheet and 15# of EPDM/Neoprene foam sheet.

The EPDM/Neoprene foam allows each sheet of lead to vibrate independently and a lead sheet has a very low resonant frequency so it will convert the frequency of the sound waves down as it passes through it as well as converting a lot of the sound wave into heat, essentially using up the sound pressure before it can get to your ears / body.

The sound from the exhaust can be absorbed, canceled to a degree with a good non flow through exhaust and the  remainder directed in an acceptable direction, preferably straight up ( unless parked under trees where it would be reflected back down to you )

The noise from the cooling fan , radiator , etc can easily be absorbed because they will be a much higher frequency range. A filter on the cooling fan inlet and exhaust will also help this.

[oltrunt]

Exactly!  Too much fun and you are right on!  I wish I had taken the time to go the extra effort on sound proofing--but I got lazy and in a hurry.  But then I'm old and I was afraid I wouldn't get the bus done before I was to frail to use it.  Keep up the effort and the fine posts.  I got as far as the double box, lead and bitumen, and dense rubber but i still have air noises your remote cooling scheme would have solved.  I've only achieved 58 db with my little 3K gas genny.  I should add that fiberglass and foam rubber seem only capable of lowering high frequency sound and your camping neighbors probably have already lost the ability to hear that anyway.  Also, plywood is best used as a sounding board--not a sound deadening material.  Jack

[Darkspeed]

Thanks Jack! 58dB is still pretty good!

[Darkspeed]

The good dB meter came in today and I got some good base line numbers

@ full speed 1800rpm
@ Injection Pump : 100dB
@ open exhaust : 107dB
@ muffler out : 94dB
@ crank case : 102dB
@ 1 meter distance 86dB

@ half speed - around 900rpm
@ Injection Pump : 94dB
@ open exhaust : 101dB
@ muffler out : 91dB
@ crank case : 97dB
@ 1 meter distance 82dB

My generator is a fixed speed unit - full throttle 1800rpm

The rpm setting affects cycles per second so 1800rpm is in the 240v / 60hz range.

Running it at half speed was significantly quiter but it would give me around 100v / 30hz which ac systems would be unhappy with.

But..... it gave me an idea.. allow me to digress into madness..

If I did a full bridge diode bank on each leg of my AC output to rectify it to a half wave DC, and combined that into a buffer capacitor, I would end up with around 80VDC / 40A which could happily feed a MPPT battery charger like a wind generator or solar would use.

So I could have two modes for my generator:

Mode A = 1800rpm AC 240V/120V @ 8kw
Mode B = 900rpm battery charging @ around 3kw - may be closer to 2.5kw - would need to test.

I would just need a contactor to switch loads and a solenoid to push the throttle from 1/2 to full throttle.

The result would be a quitter more fuel efficient way to recharge the house batteries when direct AC loads were not needed.

I wonder if there is any issue running this diesel at near idle for extended periods of time... the lower the rpm the more vibration.

BTW, totally impressed that muffler took 13dB out of the exhaust.

As a side note some of the new inverter chargers will accept some fairly funky ac inputs like the Victron Quatro for example:

Input frequency range 45 - 65 Hz
Input voltage range 180 - 265 VAC

and the Magnum:

Input frequency range 50- 70/ 40-60 Hz
Input voltage range 60 - 140/120-280 VAC

If the Magnum would actually accept 120v @ 40hz I could skip the rectifiers and capacitor for low rpm battery charging.

[eagle19952]

   well after reading this i have come to the conclusion that you exceed every requirement to be in the top 2% of nuts... 

good nuts but still nuts 

[Darkspeed]

Haha thanks...

[Scott & Heather]

No really.....Todd, you're a certified busnut...


You are spot on. I've done years of research on soundproofing and most people have no clue how complex it is. Carpet and foam the walls and you have a home recording studio....they think....sigh.

There is a special caulk out there that you can use between layers too. Super effective for acoustic projects. You can layer two sheets of drywall using the caulk between them and it does an excellent job of creating an acoustic barrier. Another weapon in the arsenal.

[TomC]

If you use a belt driven squirrel cage blower, you don't have to worry about overspeeding. I have a 2spd 1/2hp totally enclosed fan cooled GE motor. Granted, you can get a thumping sound from the belt at times, but the slower speed of the belt driven fan is much quieter than direct drive squirrel cage. Good Luck, TomC

[OneLapper]

Can't what to see the results of this project!