Silencing a Cheap Noisey Generator

Pulled from a post on a forum, and cleaned up for usage here.

Your generator can give away your state of preparedness to lots of people at just the wrong time. When they want power, and you announce that you have it, there can be conflict. To keep it and your other supplies from being “borrowed”, you need to keep it quiet enough so that only the closest people can hear it. If you can do better than that, great!

Most gensets sold are gasoline versions. The cheapest units, such as Champion, have Chinese engines that ring like bells. The engine blocks, cooling fins and generator housings all vibrate and create noise across the spectrum. There is no way to physically amend the design to attenuate this as you might address exhaust noise with mufflers. Even the thin metal used in exhaust and the mufflers create noise with each exhaust pulse.

The only way to silence a generator of the standard el-cheapo variety is to enclose it. A nice block house with baffled air supplies is great, but how many preppers can build one? What if the generator needs to be portable?

I’ve seen a couple answers to the problem, but they create new issues. Here are some thoughts on putting that thing into solitary confinement, yet still leave it arguably “portable”. There are some modifications to consider. Got tools?

Fuel Tank Concerns

Most of them have a gas tank mounted to the frame above the unit. The fuel is at risk of overheating and boiling off as fumes if left attached that way, and then enclosed. Gasoline fumes in a semi-enclosed hot box are bad news. Best to remove it and mount it above whatever silencing structure you build. Fuel tanks are made of stamped steel, welded along the mid line. They are mounted with bolts, and sometimes with rubber spacers. If you chose to relocate the tank, chose a method that allows you to safely move it, and a quick and secure way to reattach it.

The tank gravity feeds the engine, so it must be elevated. If the enclosure has a separate secondary void above the main one, the tank can be positioned there, which makes refilling it a bit more speedy in an emergency. Generators should be filled while the engine is OFF, and even better yet – when COOL. Any refilling while hot and running needs a method for redirecting spilled fuel to a safe catchment. That is a rigger’s nightmare, subject to dangerous mistakes. The best overall method to allow refueling while running is to locate the tank above and away from the engine, with no way for spilled fuel to get near the engine. Keep in mind that too distant a location requires a long fuel line, which may flow at a reduced rate, starving the engine under load.

Controlling Temperatures Within the Enclosure

In any case, the smaller the enclosure, the faster it will heat up. Even with forced air, temperatures can exceed 120 degrees in an enclosure roughly triple the size of the generator and in a warm environment. Air movement in and out is critical to controlling temps and preventing heat-related failures and shortened life. El-cheapos are not long-lived to begin with. Don’t make it worse. You will want cooling air exchanged in a volume that keeps the heated waste air below 120 degrees, if possible. Always run an exhaust fan. You may also want an inlet fan. Two fans won’t pull a lot of current. You have power right there, drive decent fans with it.

Cooling air coming in and exiting needs to go through a minimum of two openings each, offset so that the air must turn 90 degrees twice in its travel into and out of the box. This baffle helps to control noise. The more turns, the better, so long as over all volume moved remains adequate for cooling.

Use regular thermometers to monitor your temps. Inlet isn’t important. Place one inside the enclosure near the ceiling. If you are leaving the fuel tank in place, position a thermometer near the tank, but not touching it, at a position on the same side as the hottest part of the generator. That will almost always be by the exhaust manifold. Try a few positions. The other thermometer needs to be at the exhaust port of the enclosure.

Some enclosures might be simple collections a panels arranged to block direct “line-of-sight” access to the genset. This will cut down noise from obnoxious to “hey, there’s a generator somewhere over there”. If that’s all you wish to do, the rest of this is unimportant.

Some materials you might consider for controlling heat and noise. Ain’t cheap, but it is available.
CSI 25070 Heat Shield Insulation: 4 ft x 6 ft

Thermo-Tec 14130 24″ X 48″ One Sided Thermo Guard Flame Retardant

Engine Air 

Combustion air for the engine is sourced either from the cooling air coming into the enclosure, or via separate dedicated ductwork. If it is sourced from cooling air, it can be forced in by fan, or left to be drawn in indiscriminately by the cooling exhaust fan. Dedicated ductwork routes the air directly from the outside to the carburetor’s air filter box. These ducts should be flexible so they will handle vibration and movement. They can be insulated or non-insulated.

Insulated ducts prevent the heated air within the enclosure from pre-heating the intake air. In very cold climates, pre-heating is desirable for warm-up, and maybe even for operation. Under normal conditions, cool outside air is a must, and insulation helps with this. However it is supplied, the longer the air flow path, the larger the diameter of ductwork is required. Duct material needs to be of a type that will not collapse under the strain of vacuum surges as the generator pulls more air during load increases. Generally, the larger the duct, the easier it is for straight section to collapse when flexible material is used. Pre-filters at the outside of the box will decrease pressure within the intake duct. If the ductwork can handle this, the pre-filter will serve as a means to silence the noises created by the engine’s intake.

If the engine is left to use air at random as it is pulled into the enclosure by the exhaust fan, it will be much warmer than outside air. Cold air intakes help an engine run cooler. Keep these facts in mind when designing for your climate.

Enclosure Materials

The enclosure box, if built to be semi-portable, tends to be constructed using lightweight materials in combinations /layers. Rigid construction with hard surfaces tends to act like a sounding board via vibrations. Deadening the impact of noise on the inside of the box is the key. It is also a concern for fire if the material is close to the generator surfaces and subject to great heat. Some people have successfully used fire-resistant carpeting. They test it using torches. Others have used under-hood automotive insulation in layers. Any fireproof material can serve as a protection layer between sound deadening materials and the outer casing. Whatever you decide to use, subject it to great heat (torch) before building the box. Include a way to test for operating temperatures if you are unsure. Lightweight particle board or even MDF can serve as an outer shell. You can find engine heat shields and deadening material on the net, but it isn’t cheap. It is available at some junk yards, but it won’t be the cleanest stuff you’ve worked with. As cars run down the road, all manner of grit and grime splash up into the engine compartment and coat the material. It is hard to clean without a vacuum, and power heads will tear it up.

Engine Exhaust 

If you route the engine exhaust up and away from the box, insulate it. Keeping exhaust hot also keeps gas velocity high. The insulation also prevents vibration within the exhaust tubing from creating noise outside the box. The end of the pipe may be constructed to widen out quite a ways, diffusing the hot air into the cooler air, and minimizing noise-creating exhaust pulses with each cycle of the engine.

Engine exhaust should pass through the box via double-walled rigid-piping, and be turned down on the outside to prevent rain or sprinkler water from running into the engine. Any bend helps cut down noise. Extra mufflers might lower the sound, but may also increase back pressure in the exhaust, causing increased heat buildup in the engine. To further reduce noise and protect against overtemp, wrap exhaust duct insulation around the pipe.

If in doubt, when you build one of these TEST FOR HEAT. Controlling heat and preventing fires is the biggest problem when silencing an outside generator.

Alternate Enclosure

The above design could conceivably be built for portability. It could go on road trips or bug outs. For noise control of a portable generator in a semi portable setting, you might want to consider burying the thing. A pit large enough to contain the whole unit can be covered with a thick sound-proofing panel. Most of the noise would be absorbed by the earth. Methods for feeding air to it, and removing exhaust would be variations on what is described above. With a ramp cut into one end wall, the genset can be removed at will for servicing and other activities.

You could also build a 3-walled cinder block enclosure. The fourth wall would be a thick sound proof door, and the roof a similar version of that. Leave yourself a minimum of three feet of space around all sides of the generator for servicing. Go for five feet if you have the room or, if you must go with a small room, set the generator on lockable slides so that you can push it against a far wall as needed. It seems we all want more space than we originally plan, so think big.

Safety

  • Here are some “nevers” for you. Someone will have an answer for all of these, but I don’t. Death is irreversible.
  • Never run a generator in an enclosed space. CO will kill you. Fire will kill you. Your pissed-off cohabitants will kill you.
  • Never run a generator near an open door, window or any opening near a habitation. CO will kill you
  • Never store fuel inside a building. Fire and /or explosion will kill you.
  • Never store fuel right next to a generator. They can catch fire, and ignite the fuel. Explosion and fire will kill you.
  • Never refuel a generator while it is running, unless designed to do so.
  • Never run a generator dry while under load. The lean fuel condition at the end, combined with the EMF clamp will kill the generator, or harm it.
  • Never start a generator with a load connected unless it is specifically designed to do so. Even then, it will live longer if you connect the load after it has warmed up.
  • Never work on a hot generator unless some crazy unique situation absolutely requires it. Burns in a austere scenario can become infected and, (you got it), can kill you.

Be safe. Remember to test your generator regularly and refresh the fuel in the tank, unless you store it dry (recommended).

 

 

 

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