Sunday, October 29, 2017

Generator Noise

I took some time a while back to see what could be done to help quiet the generator.   Most of the noise on mine is mechanical noise from the unit itself.  Remember that I have a Fuse 23A so the generator is mounted underneath, centered at roughly the head of the beds.

I even asked Onan about what could be done. They were up front and said not much since the QG2500 is just noisy.   They said that the best that could be done was to put it in a soundproof box.  That won't happen on the Fuse since there is not an easy way to do it and keep airflow.

QG2500 - copyright Onan

But I did take a look.   Tried a couple of things and found some areas I need to give some more thought to.   I tried to find places where there was metal on metal contact.  I also looked for places where sound could reflect and reverberate.

When I went underneath and looked around I saw a couple of things that were interesting:
  • The generator is in its container with some soundproofing inside, but mounted to the motorhome without any isolation pads that I could see.
  • The cooling appears to be from the front panel and blows through and straight down coming out near where the exhaust comes out.  A huge amount of noise comes with this.  I am pretty sure the noise is bouncing back up.  
    QG2500 Air flow
  • Above the generator is a metal plate.   There is a 6-8 inch air gap between the top of the generator and this plate.
  • To the passenger side is a metal panel.  This appears to be the rear of the storage compartment.  There is an I beam above this space.
  • To the rear (or the generators front) is the black tank
  • There is no undercoating apparent.
  • Where the exhaust comes through the generator mount is very tight.  On my unit the exhaust and exhaust clamp touches the mount.   This is an issue.
    Exhaust routing
So I took some time and tried to attenuate the sound.   I was concerned about affecting air flow, so I was rather careful.  I tried a couple of things:
  • I applied some 80 mil Dynamat (actually Noico Sound deadening mat) to some of the surfaces around the generator.
    • I put some on the metal pan above the generator.   This appears to be part of the subfloor so doing anything here could quiet sounds getting into the living space.  
      Dynamat above Generator
    • I put some on the metal that makes the back of the lower passenger storage compartment. from the generator.  It was a large flat surface and had some vibration.  In this case there was still vibration afterward.  This area is just not stiff enough not to move.  Some foam is needed behind the metal inside the storage compartment.    
    • I put some on the black tank surfaces facing the generator.  
    • I put some on the surface of the I beam, but not in the open area. 
    • I used around 4 sq. ft of the material.  It did seem to make a difference.  Not a difference in how loud, but it made the noise more lower note.
  • I took a good look at the exhaust system.  
    • I followed the heat shield to make sure it was not making contact anywhere (it was not).
    • I looked at the area where the exhaust passed through the generator mount.   This is a huge area for improvement.  The exhaust pipe touches the mount and the pipe clamp touches the generator mount at this point.
    • I put a little exhaust wrap (HM&FC Titanium Exhaust Wrap) in that area to try and get rid of any metal on metal contact.  This helped somewhat.   I need to think about doing some more here.   The exhaust is resting on the mount and I could not get anything under the exhaust pipe.   
Metat on metal contact

So what were the results?   It helped a little but not significantly.   But I do have a couple of more things to look at:

    • Any way to isolate the exhaust from the generator mount.  
    • Move the exhaust clamp next to the generator mount out slightly away from the mount.  Maybe 1/16 -1/8 inch.
    • Foam as opposed to Dynamat in the I-beam void
    • Foam on the back of the lower storage area.  This backs up to the generator space.  The panel still sounds like it reverberates noise from the generator since it is not very stiff. 

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