Dear Tom and Ray:

Say I have an electric car (one that runs on nothing but electricity) that can be charged by plugging into any outlet. But for cross-country trips or long trips outside my car's range, I carry a 120-volt Honda generator and a gas can in the trunk with me. Could I just pull over when I need to and charge up the car? Would that work? How much charging from a gas generator would it take to charge an electric car?

-- John

TOM: John, you've just invented the plug-in hybrid! Again!

RAY: This is exactly the idea behind parallel plug-in hybrids, like the Chevy Volt. They run on electricity until the electricity runs out. Then they use a gasoline engine to "generate" more electricity to recharge the batteries or move the wheels.

TOM: So your idea is not far-fetched. However, its execution is. If you do this yourself rather than let General Motors do it, you lose both convenience and efficiency.

RAY: In the Volt, you don't have to think about it. When the batteries run down, the engine automatically starts up, and you can just keep right on driving -- for hundreds of miles -- on gasoline power.

TOM: With your plan, you'd have to find a place to stop and run the generator while the car is parked. And you'd have to always carry a loaded gasoline can in your trunk, which is not recommended.

RAY: Plus, your plan isn't practical right now. The charge time at 120 volts, for an all-electric Nissan Leaf, for example (which goes about 85 miles on a charge), is about 20 hours.

TOM: That means on a cross-country trip, you'd drive for about an hour and a half, then have to stay overnight and run your generator to charge up your car. The hotel bills alone will kill you! That is, if your fellow guests don't revolt against the noise from the generator.

RAY: You could get a bigger, higher-wattage generator, and cut your recharge time down a bit using a 220-volt outlet. But then you might have to tow that generator behind your car, and that would cut your range to about 50 miles per charge. So there's no great homemade solution for long-distance electric driving here.

TOM: In time, there will be faster charging systems. And quicker-charging batteries. Or even battery swaps, where you leave your old one at a "filling station" to be recharged for the next guy, and take a fully charged one with you.

RAY: But for now, your idea is on the impractical side, John. But keep thinking!