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More Advanced Technical Discussion of the Power Inverter, by Bruce Bernhart

In part 1, we discussed square wave inverters and how they compare with true sine wave power converters.

The problem with wave form only comes into play when specialized pieces of equipment need to be powered. Here are a few devices which could have problems when they are connected to an inverter producing a modified-sine wave signal: oxygen concentrators, fax machines, laser printers, high voltage cordless tool chargers, equipment with variable speed motors, electric shavers, and garage door openers.

A power converter typically has four terminals. Consult the instructions provided with the device, and wire it accordingly. The four terminals will be printed or embossed with their function, and the usual lay-out of color-coded wires to terminals is to connect the coach battery feed terminal to a red or black wire; connect the coach battery negative terminal to a white wire; connect the shore power hot terminal to a blue or black wire; connect the shore power neutral terminal to a white wire.

There are a few other applications- high-end audio video units, plasma displays, gaming systems, and certain scientific testing equipment -- for which true-sine wave is not usually required. Even so, these applications can usually benefit from the improved clarity of the electrical signal produced by a true-sine wave power inverter. Users of these particular items have usually spent a lot of money to achieve optimal results from their equipment, and it would be a shame to have a cheaper modified-sine wave signal cause inaccurate readings on a piece of scientific equipment. It would be equally disheartening to have small distortion lines appear on a $3000 plasma TV because the user saved $250.00 by buying a modified-sine wave power inverter.

It is also important to understand that there is no way to upgrade or clean a modified-sine wave signal. If your item does not work on a modified-sine wave inverter, you will need to purchase a new true-sine wave power inverter. Users on a tight budget might want to consider only enough true-sine wave power to run required equipment and purchase a less expensive modified-sine wave inverter to run the rest of the load. The Xantrex XS400 ($375-$400), a true-sine wave power inverter, is often used to power only the audio video loads in RV applications. The rest of the RV's electrical loads are often powered by a larger modified-sine wave power inverter.

Many people are surprised at the overall improvement in signal quality when using inverters on audio/video applications. They notice that there are fewer distortions and few if any interference lines. While true-sine wave inverters are not recommended for everyone, customers with no budgetary concerns should choose a true-sine wave product. They can then rest assured that their inverter will be able to handle anything they plug into it. Many stores do not carry true-sine wave power inverters because the price is often significantly higher than their modified-sine cousins -- usually two to five times more. Generally, expect to pay $200 to $3,000 for pure-sine wave inverters depending upon how many output watts are needed.

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