Could your car be used as a source of electricity in an emergency?

Dear Car Talk

Dear Car Talk | May 01, 2003

Dear Tom and Ray:

Here's a burning question that I have wanted to ask: Can a car be used as an emergency source of electricity for a short period? Here's the deal: You can purchase "converters" that turn 12-volt power into 110-volt AC boxes. If a person were to hook up a heavy-duty one (40-60 amps) directly to a car battery, assuming the gas tank was full, how long would the car run at idle to support a 40-amp load? Would it damage the car to use it like this? Is this a practical source of emergency power? -- Dennis

RAY: Well, if you are willing to modify your amperage demands a bit, I think we can work with you.

TOM: Right. You'd have to be willing to give up the vibrating chair massager and the floodlit statue of Michelangelo's "David," at least until the regular power came back on.

RAY: The devices you speak of are called "inverters." And, like you say, they convert 12-volt DC power into AC power you can use to run lights, tools and appliances. The heavy-duty ones tend to provide 16, 20 and sometimes 25 AC amps of continuous power. The most we'd recommend for use with a car, even with a heavy-duty (100 amps DC) alternator, is about 16 amps.

TOM: That's enough to run, say, a refrigerator/freezer (5 amps), a 19-inch color TV (1.5 amps), a couple of light bulbs (1 amp) and the microwave (8 amps). Basically, everything modern man needs to survive.

RAY: And you'd have to keep the car running continuously so the alternator would keep the battery charged. If you didn't, the car battery's voltage would drop, and the inverter would automatically shut off. Possibly in the middle of "Baywatch."

TOM: How long would the car run? It'd run all day. Without a heavy load on the alternator, an idling car can run for more than a day -- depending on the car and the size of the gas tank. While powering an inverter, it won't run that long, but it should be more than enough if you're using the inverter for short-term emergency power (i.e., a few hours when the power goes out), Dennis.

RAY: To find out more, there's a lot of useful information at a Web site called Now if you'll excuse me, I have to go start my car, hook up my inverter and fire up my electric heated wave pool.

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