PORTABLE INVERTER GENERATOR:

COMPARISON, REVIEW AND A SELECTION GUIDE

In conventional electric gensets, the output is a raw voltage induced in a coil by a rotating magnetic field. Unlike grid-supplied electricity, this voltage is not a pure sine wave and may contain significant level of higher frequency harmonics. While total harmonic distortion (THD) of less than 5-6% is generally considered acceptable, some portable gensets produce THD>15%.

If you connect your load via a UPS power supply, it may not even recognize power produced by such a genset as normal power and may switch to battery mode. In addition to this, cheap portable gensets may not have an automatic voltage regulator (AVR), can't react to rapidly changing loads and will produce power surges or sags. They may even destroy an appliance sensitive to voltage fluctuations, such as a refrigerator's compressor. The cleanest power of all sources is produced by sine wave inverters, which are best for sensitive electronics. That is why many genset manufacturers introduced the inverter technology into their models.

INVERTER TECHNOLOGY

By definition, inverter generator is a device that includes an internal-combustion engine, an alternator and an electronic DC-AC converter integrated into a single appliance. Technivally speaking, inverters are DC-AC converters- they require DC input. That's why the voltage from an engine driven alternator first has to be rectified. Normally, a genset with inverter technology uses an alternator that produces a 3-phase voltage. This voltage is rectified and converted to DC, which is then converted to a clean sine wave AC. The conversion is normally done by a microprocessor controlled solid-state power converter circuit operating in a PWM mode. A 3-phase system is used because a 3-phase rectifier has much lower ripple factor that a single phase rectifier. Accordingly, such system needs much smaller filter capacitor (if any) to lower AC component to an acceptable level. Besides generating high quality power output, inverter generators are more fuel-efficient and quite. Note that the frequency of the voltage induced by a rotating magnetic is directly related to the frequency of the rotation. Therefore, in conventional portable gensets the engines have to run at a constant speed. For the US market it is 3600 RPM for 2 poles or 1800 RPM for 4 poles to produce 60 hertz. As the result, even when the motor is idle, its fuel consumption is as much as half of the consumption at rated load. In contrary, in inverter generators the engine can run at lower RPMs because the induced voltage is rectified anyway. In addition, the engine does not have to run at full speed constantly. It automatically adjusts depending on the electrical demand. All this makes it more fuel efficient and much quieter. Most consumer grade inverter generator models available on the market are low power portable. Their light weight and low noise make them a popular choice for camping applications. Note that just like all engine-driven devices, inverter generators produce harmful carbon monoxide exhaust and should be used only outdoor.

PRICE COMPARISON

There are a number of manufacturers of portable inverter generators for home, camping and commercial use, such as Honda, Yamaha, Honeywell, Generac, Briggs and Stratton, Kipor, Eastern Tools and Equipment, and other. Inverter generators typically cost 2 to 5 times more than traditional gensets. You can find a cheap gasoline genset for sale for less than $100/kW, but a generator with inverter technology typically sells for $250/kW and up. Honda and Yamaha models have top ratings based on the user reviews, but they also are priced at the high end of the market price range. These two brands cost typically $500/kW and up. Domestic manufacturers are generally less expensive, but based on the customer reviews at Amazon they may be more noisy, may have lower reliability and lower ratings.

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