Pure sine wave inverters can...
Pure sine wave inverters can deliver power as clean as your utility company, so there is less risk of interference patterns and humming noises. They cost more but are a better choice for running sensitive equipment, such as laptop computers, oxygen generators, and microprocessor-controlled laser printers. This is a 300-watt unit made by Samlex.
Inverters are rated in both continuous watts and surge power. Surge power is the output an inverter can supply for a minute or two in order to start up certain tools, pumps, and air conditioners.
As for continuous wattage, it is always wise to get an inverter capable of delivering more wattage than you expect to need at one time, with a capacity 15-20 percent greater than your largest load. A light-duty inverter that plugs into the vehicle's cigarette lighter socket might deliver 180 watts of continuous power, good enough to power a laptop (50-75 watts) and a small inkjet printer (75 watts). However, a workstation with a PC, a monitor (400 watts), and a printer might consume 475 watts, requiring at least a 500-watt inverter. It might take as much as 1,100 watts to run a vacuum cleaner, 2,000 watts to run a microwave oven, or 1,500 watts to heat up a toaster. A 1hp air compressor might need 2,000 watts to run and require a startup surge of 5,000 watts.
Many appliances will have a label on the bottom showing their wattage draw, but if not, tables showing average current draws for various appliances are on the Internet, and most manufacturers list current draw specs on their websites. (If the draw is given in amps, multiply by 120 to get watts.)
As a rule, startup voltage is generally about twice the continuous load for any given appliance, but there are notable exceptions. Induction motors, such as air conditioners and refrigerators, may require steep startup surge voltages, sometimes three to seven times the continuous operating voltage, so the peak-surge capacity of an inverter is critical when powering that type of appliance.
A strong performer for larger...
A strong performer for larger loads that demand a clean, pure source of AC power, the Go Power! GP-SW1500 can run appliances and sensitive electronic equipment like TVs, stereos, and computers.
It doesn't take much shopping to notice that prices vary widely. One reason is the quality of the electricity an inverter is capable of delivering. Inverters known as pure sine wave or true sine wave cost more but deliver electrical output with very low harmonic distortion, much like the electricity we get from the utility company at home. Pure sine wave inverters reduce the audible humming ordinary inverters (called modified sine wave) can cause in appliances like fans, fluorescent lights, answering machines, and audio amplifiers.
Modified sine wave inverters, also known as square wave inverters, are much cheaper but can create visual interference patterns in plasma and LCD TVs and game consoles. Some devices, such as laser printers, certain laptop computers, fluorescent lights with ballasts, or anything with microprocessor control (digital clocks, variable-speed tools) may not work with modified sine wave inverters.
However, modified sine wave inverters are about five times cheaper and work fine to run lights, coffee pots, microwaves, vacuums, and other devices that are not controlled by microprocessors. For example, we saw prices for 400-watt modified sine inverters as low as $29, while a 300-watt Samlex pure sine inverter was priced around $160. The difference may be steep, but the benefits of a pure sine wave inverter justify the higher price, where one is truly needed.
A workable strategy would be to use a larger-output modified sine wave inverter for most appliances and keep a smaller, true sine wave inverter on hand for sensitive appliances like laptops and medical equipment.
Other desirable features worth paying are cooling fans, low battery alarms, battery discharge protection features, and visible LED display ladders that track input voltage and output wattage.