So, you just got your hands on a inverter generator that is advertised to be “conversation loud” at 25 feet? Yeah, I’m not that impressed either. Why is it that my car and truck are both quieter, and have considerably larger engines?

Mechanical Noise

Generators have a few noisemakers that aren’t well insulated.

  • Usually single piston design = unbalanced mass (think of a Harley motorcycle shaking vs a car)
  • Noise of combustion from the cylinder
  • Noise of camshaft, cam chain
  • Inverter coil cooling fan (a big one)

So, why not just route the exhaust outside and close the generator up, like in a insulated room, like I did with my RV?

It worked well, in my mind

There’s a few problems with my really simple solution. First, the generator transferred all the vibration to my RV’s floor/frame, making the whole floor shake, and some cabinets rattle. Second, the exhaust was still “unacceptably” loud to me, each exhaust pulse echoed around the bottom of my RV like a bass cannon. Lastly, and the most important, I almost set my generator on fire due to the ambient heat of the engine, heat given off from the exhaust and the inverter cooling fan.

The thing is, it ran perfectly at first under little load. The second I cranked up a peak load the engine worked much harder, throwing off a ton more heat. The compartment became so smoky (in thanks to painting my exhaust and it burning, always use a high temp paint for exhausts) that thankfully, the engine died and I went out to inspect it before it melted.

The solution is to build a generator quiet box to enclose the generator inside. Just like your car’s engine bay (ever notice you usually have a sound panel on your hood?)

Exhaust

Small generators are space compact. The mufflers are fantastic for the size, yet still inadequate (or so I think). So, stick a car exhaust on it, right?

No so fast. Car exhausts are engineered to silence a much larger flow of exhaust gasses than what our little single piston generator can put out. This means that the internal baffling isn’t designed to quiet the (slow, in this case) exhaust pulses.

Let’s take a look at how motorcycle exhausts work.

How knuckleheads make Harleys annoyingly loud. NEVER screw with fiberglass without a particulate mask on, like these schmucks!

The solution

So, we have two sources of noise. We know that we can quiet the exhaust by packing a muffler with fiberglass. We know that we can quiet the mechanical noise with an enclosure.

Here’s an example with my Champion 3500w inverter.

Muffler


38mm Motorcycle Scooter Exhaust Muffler Pipe W/Movable Silencer

With this external muffler pipe & “38mm” (1.5″) muffler exhaust, I can reroute and quiet my generator’s exhaust. The “silencer” (baffle) is removable from the muffler, which I can repack with fiberglass.

Lastly, I need to keep the hot piping cool, so I don’t set my box (or me) on fire. Then I can easily mount it wherever, like a generator quiet box?

Exhaust Wrap

Box

120mm 110CFM fan duct with dryer vent weather resistant duct I designed & 3D Printed

Generators need to stay cool! Ventilation should be somewhere around 65 CFM per kw.

I picked up 2x 110CFM 120V 120mm fans that I’ll be mounting in the box, along with exhausts.


AC Infinity AXIAL 1238, Muffin Fan, 115V 120V AC 120mm x 38mm High Speed

I have some latches, hinges, etc coming as well, along with a 12 Gallon marine fuel tank (but that’ll be for another post).

The plan is to build a quiet box and enclose it with egg crate foam! Slap in the required CFM fans for cooling, mount the muffler on the outside of the box to keep it compact. Extend runtime massively with a 12 Gallon external fuel tank.

Now I just need to patiently await my parts to come, and I’ll be posting up how it all turns out! If I’m right, you should barely be able to tell that the generator is on, all while staying cool.

Subscribe to my blog for updates! I have a ton of cool stuff coming!

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