Inverters


Inverters are electronic devices that change battery voltage (normally 12 volt DC but it can be any low voltage direct current) into regular household current (110 volt AC) for operating tools, appliances and other common electrical equipment. Inverters are of three basic types: sine wave, modified sine wave and square wave. This distinction refers to the quality of the electrical output of the inverter and the types of electrical devices the inverter can successfully operate. Electricity that you can receive from your local electrical utility company is sine wave and is the best form of electricity. Good sine wave inverters are starting to show up on the market now but are fairly expensive. If you are operating sensitive electronic equipment such as televisions, radios or computers and want top quality performance, sine wave inverters are the way to go. If you can tolerate the possibility of minor distortions there are several excellent modified sine wave inverters on the market. The prices on modified sine wave inverters are very competitive. Consequently, they are presently the best choice for the majority of applications. Square wave inverters are still available and are inexpensive but they will not operate certain types of equipment, such as induction motors, and will create noticeable distortion and interference. The prices on modified sine wave inverters are now low enough that square wave inverters are becoming a thing of the past.
WHICH INVERTER IS BEST FOR ME?
If your requirements are very specialized, sophisticated or sensitive (such as computers, laser printers, test equipment, radio equipment, audio recording equipment or motors with SCR speed controls), sine wave inverters are the best choice. If your requirements are simple and you are willing to put up with limitations and potential distortion, square wave inverters are a very inexpensive way to get started. For most applications the modified sine wave inverter is the best choice. It has eliminated most of the limitations of the square wave inverter, it can provide you with a variety of options to enhance the performance of your electrical system and the prices are very competitive.

Review the options available for the inverter. Many inverters are available with features such as corrosion resistance, overvoltage protection, overheating protection, low voltage protection, battery charging capability, 240 volt capability, voltage and amperage monitoring, and automatic load sensing. If what you need is portable power for occasional use on shop truck, these options may not be beneficial, but if your inverter is to be part of a home power or marine system they can be invaluable. The qualified technicians at SOLAR ALASKA can discuss the various styles and options with you in more detail and assist you in the selection of the best type of inverter for your needs.


HOW DO I SELECT THE PROPER SIZE?

Inverters are normally sized by output wattage capability. Understanding a couple of simple concepts will enable you to select the proper size for your needs. First, the inverter will normally have two ratings with respect to output capacity. The first is the wattage that it can sustain on a prolonged basis. This is normally the published rating. For most inverters it is the wattage that the inverter will support on a continuos basis, but not always, so check the specifications to verify. (The Trace 812 inverter, for instance, is rated at 800 watts but this is the wattage it will sustain for 1/2 hour. Its continuos rating is 675 watts.) The second wattage rating is that which the inverter can support on a short term basis for momentary surges in demand and is called the surge capacity. All electrical devices require more electrical current to start than to run. For some devices, such as fans or computers, this additional starting wattage is minimal. For other equipment, such as water pumps and refrigerators, the starting wattage requirements can be three times the operating wattage requirements. Check the surge capacity rating to ensure that the inverter will operate and start your electrical devices.

The second concept to consider is the conversion efficiency of the inverter. This refers to the amount of electrical loss that is incurred in converting the electricity and can be extremely important if battery power is expensive or difficult to replace. The amount of loss is influenced by the quality and type of inverter and by the percentage of the inverter capacity being utilized. All inverters have an optimal efficiency range and most good inverters will have a conversion efficiency of 95% or better in their optimal range. It is important that the inverter be sized so that it is normally operating in its optimal efficiency range. A 95% efficiency means that 5% of the power is being lost in the conversion process.

In comparing the output capability of the inverter to your electrical requirements, remember that, at 110 volts AC, one amp equals 110 watts. If you have a skilsaw that uses 7 amps to operate and 15 amps to start you will need 770 watts and 1650 watts of inverter power respectively. The qualified technicians at SOLAR ALASKA can assist you in assessing your electrical load requirements and properly sizing your inverter.


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