Q: In order to power a few 120-volt items while driving, we are using an inverter plugged into our vehicle's cigarette lighter socket. When the car's running, is the socket and other electronics (lights, radio) powered by the alternator, having little effect on battery life? Or are all the electronics powered directly by the battery, with the alternator simply working to keep the battery charged?
I'd rather not ruin my battery.
I read that deep-cycle batteries can be run down to about a 50 percent charge, while normal batteries shouldn't be allowed to dip below 90 percent.
What do you think?
_James
A: Before I answer, let me provide a little additional information to all my other readers.
Earlier this summer, while driving home from Alaska, I met James and Bel at a petrol station (their term) in Watson Lake, a town in Canada's Yukon territory. We've stayed in touch by email ever since.
They were driving the most interesting vehicle: a Mitsubishi Delica, a right-hand, four-wheel-drive microvan, which they had packed full of road trip supplies. The duo, from Vancouver, British Columbia, had driven north to Prudhoe Bay, Alaska, and were heading south _ way south _ to the lower tip of Argentina. Their incredible trip, including some spectacular photos of it, can be followed at www.theoverlanders.tumblr.com.
But back to James' question.
A vehicle's battery is intended to start the engine, provide accessory power _ to a point _ when the engine isn't running, and serve as backup if the alternator can't meet all the needs while the engine is engaged.
When you're driving, the alternator ought to create all the energy the vehicle needs up to the point of its production limit, which in James' case is 65 amps. The sum of an engine's electrical consumption (management, fuel, ignition systems) and the vehicle's headlights and radio should be about 20-25 amps, leaving a nice reserve before the battery would be called upon to help out.
James' cigarette lighter-powered inverter (likely 150 watts) might pull as much as 10-15 additional amps of current from the alternator when at full output, resulting in a total pull still within the alternator's comfort zone.
Larger inverters are sold, but using one might result in popped fuses or smoldering sockets. Hardwiring directly to the battery with short, thick cables is the solution. Before doing that, check the labels on your accessories to determine their wattage.
It's best to employ an inverter only with the engine running and, yes, to not discharge a battery below certain charge points. Drawing 10 or 15 amps from a typical battery when the engine's off would drain it to the point of a no-start condition in about three or hour hours.
James' Delica is equipped with two batteries. By using a battery selector device, he could, when parked, isolate the batteries, using one for minimal inverter use and the other solely for starting. He could, when then hitting the road again, re-engage both, allowing them to charge.
While stationary, using a 100-watt solar panel (they measure about 27 inches by 40 inches and cost about $120 online) could, under optimum conditions, provide 6-7 amps of charging current for the battery. Eight hours of bright sun could compensate for about four hours of inverter use. A charge controller would be needed if you want to use the panel on a continual basis or if you want to use multiple panels.
