Question: I'm thinking about buying a 110 volt converter to plug in to my lighter. It seems like such a neat deal to be able to plug in my laptop, cell phone charger and a few other things I haven't even thought of yet. What should I look for when buying one of these? How many things can be plugged in at the same time?

Answer: Power inverters change your car's 12 volt direct current into 120 volt alternating current, similar to what's used in your home. I used the word similar because the more common, lower priced inverters produce what's called a modified sine wave. Instead of a smooth and curving alternation of current, it looks like something you'd create on an Etch-a-Sketch. This works well for most devices and personal electronics power supplies, but can cause issues with some electronic devices, medical equipment, and inductive loads (electric motors, microwaves). Pure sine wave inverters are available that work well with all devices, but they cost about 3-4 times that of the modified sine units. To be safe, check with a device's manufacturer about modified sine wave compatibility.

Power inverters come in all sizes, from tiny to large enough to run your home. Units capable of supplying 300 watts or less can be plugged into your lighter socket, although loads above 200 watts may overheat the socket or blow the lighter fuse. Larger inverters need to be clipped or connected directly to the battery (always with an appropriate fuse) and mounted as close to it as possible. Large diameter wire (6 gauge - almost pencil diameter) or larger will likely be needed if the inverter is to be mounted inside the vehicle or in the trunk.

What size inverter? You'll need to total up the wattage of the devices you plan to power and consider the huge start-up load of some motor powered devices. Based on the items you mentioned, a 750 watt inverter, about the size of a cigar box, might be a good choice. These run about $75 for modified sine wave or about $275 for pure sine wave and will require a direct battery hookup. It's important to remember the larger the inverter and the loads it powers, the quicker you'll drain your battery if used with the engine not running.

If you're not sure about the wattage of certain household powered devices, a neat gadget called a Killawatt, made by P3 International, can be used to measure them. This tool is fun to use and could save you a lot of money by learning and managing your household energy usage as well as knowing what can be plugged into your inverter. They're widely available on the Web for around $25. While there, consider a look at Donrowe.com's very informative inverter FAQ page.