Quiet Power Generators 101
At the most basic level a portable generator is a piece of equipment that utilizes a fuel source in order to produce mechanical energy that is then converted into electrical energy. While there are many ways to classify power generators the broadest and most important is into one of two categories; Conventional or Inverter.
What’s the Difference Between an Inverter Generator and a Conventional Generator?
In short inverter generators are able to run at variable speeds relative to the applied load (how much juice you are currently using). They are typically smaller, quieter, more fuel-efficient and produce a ‘cleaner’/more refined AC than conventional generators. Conventional generators, however, have a longer run time and are able to produce greater outputs (more watts). Below is a more detailed breakdown of the differences between these two and how these differences affect their applications.
Conventional portable generators use a fuel source such as gasoline, diesel or propane in order to drive pistons within a combustion engine. Through the process of electromagnetic induction an alternator converts this mechanical energy into electrical energy. A conventional generator requires the engine to run at a constant speed of 3600rpm in order to produce a consistent frequency output of 120v AC at 60 Hertz.
Inverter generators function a bit differently. As with conventional generators they also utilize a fuel source in order to produce mechanical energy. The process by which this mechanical energy is then converted to electrical energy is where the difference arises. An inverter generator produces an electromagnetic field by passing ceramic magnets around a central stator. This produces AC that is then directed through a Rectifying Bridge Diode. The RBD effectively converts the AC energy into DC. This DC is then used to power an inverter which, true to its name, ‘inverts’ the DC back into AC that we can then use to power our electronics. This complex process of converting the electricity from AC to DC and then inverting it back into AC has the effect of producing a much ‘cleaner’ or higher quality power source. Since the generating portion of an inverter is much smaller than its conventional counterpart, inverters are typically much smaller and quieter than conventional units.
This is a major factor to consider when purchasing a generator- after all the last thing you want to do before your RV trip is throw out your back. Unfortunately with greater wattage comes greater weight. The trick is to purchase a unit that has enough ‘uumph’ to get the job done without too much overkill. Inverters are typically going to have the upper hand when it comes to portability. The ‘generating’ portion of an inverter is much smaller than their conventional counterparts thus the overall size of the unit is diminished. The Briggs and Stratton 30545 is built with a very convenient dual handle system which enables you to share the load when lifting is necessary. It also features luggage style wheels and a telescopic handle which makes transportation that much easier.
Not only does a fuel efficient, quiet power generator keep the environment happy it keeps your wallet happy as well. Conventional generators rely on a mechanical governor to keep the engine running at a constant 3600rmp regardless of the load applied. Inverters, by contrast, are able to operate at variable speeds thus they are much more fuel-efficient. For instance the Westinghouse WH2400i is able to run for 11 hours at 1/4 load on a single tank of fuel. While conventional generators are typically built with larger fuel tanks thus allowing longer running times, inverter generators, which are built for greater portability, often possess smaller fuel tanks. This, however, is offset by their ability to run at variable rpms thus enabling better fuel-efficiency.
Not all generators are created equal and the same is true of AC power. While both conventional generators and inverter generators produce AC power, an inverter produces a much superior sine wave. Why does this matter? Well in order to safely run/charge sensitive electronics such as laptops, smartphones and televisions a clean power source is necessary to ensure the microprocessors within these devices will not be damaged. A sine wave’s purity is measured by its Total Harmonic Distortion. Sensitive electronics require a THD roughly ≤ 5%. Conventional generators, however, typically produce THD’s around the 9% range. This is fine for most power tools, space heaters and light sources. Inverter generators on the other hand ‘clean’ the power by converting the AC into DC and then inverting it back into AC. Inverters therefore produce THD’s around the 3% range thus making them compatible with our beloved microprocessors.
Unfortunately, inverters with their smaller engines typically come at the expense of larger power outputs. That said most larger inverters such as Champion 75537i would be able to handle a typical 13,500 BTU air conditioner. While Honda has managed to produce inverters such as the 7000W Super Light Weight Inverter these units are very expensive and blow the budget of your average RV enthusiast. Luckily, for those who require larger power supplies, such as those who use generators to power 15 000 BTU AC units, there is a solution- paralleling. Paralleling consists of connecting two inverters together and running them simultaneously in order to double your power output. Most inverters these days allow for parallel operation and are built with special ports for this function. The connection cable is generally sold separately and will run you around $70. There are two major benefits of paralleling two inverters together as opposed to purchasing a single larger unit. The first is portability. Two smaller units are much easier to move than a single, heavy unit. The second is noise control. Running two smaller inverters will enable to to double your power output without doubling your noise pollution. This is not true of larger single units.
If great power comes with great responsibility then it also comes with great noise. Or at least it used to. With the advent of inverter generators came a new era in portable power. Simply put inverter power generators are quiet power generators. This is not to say that they are silent. They are, however, acoustically superior to their conventional brethren. For many, noise pollution (in conjunction with price) is perhaps the most important factor when purchasing a power generator. There’s nothing like an overly-loud generator when it comes to making “friends” in the RV park. In the domain of noise inverters invariably win. Their smaller engines and sound attenuating chambers simply emit less noise. The WEN 56310i for example only produces 57dBs under 1/4 load.
Sound and Decibels (dB)
We measure how loud something is using decibels. While a detailed exposition of decibels is quite honestly beyond me it is fortunately beyond what you need to know when making an informed decision on generators. There are, however, a few important bits of information that are important to understand in relation to generators.
1) The decibel system is logarithmic not linear. This is import as you may be comparing a generator with a dB rating of 53 to a generator of 59 dB. While this 6 point dB difference may not seem much, prima facie, we would actually perceive the latter generator as being TWICE as loud.
(A small caveat: some websites will state that an increase of 3 on the decibel scale corresponds to a doubling of volume. This is not entirely accurate but would require a long-winded explanation of amplitude ratios and sound pressure- all of which is superfluous to buying a generator.)
The important notion here is that small differences in dB ratings make a big difference.
2) dB ratings should be taken from a measurement of 23ft. This is not to say they actually are. Some companies do not list the distance at which a measurement is taken and we are left to assume they are following best practices. In addition it is worth noting that some manufactures will give a dB reading at ½ load whereas some will use ¼ load measurements.
3) A generator placed twice as far away will appear 1/4th as loud. While it goes without saying that the further you can place your generator away the better off you’ll be, it is interesting to note that sound is diminished exponentially as you move further away from it. Twice as far away will result in 1/4th the noise. Three times as far away will result in 1/9th the noise and so on.
Fun fact: the smallest audible sound that can be heard by a healthy human ear receives a decibel rating of 0 and corresponds to 10-12w/m2 (watts per meter squared). The point at which sound becomes painful is around the 120 dB range and is ONE TRILLION times (1,000,000,000,000) as loud as a dB rating of 0.