Inverters handy to have on a boat

Think you can’t catch fish in Sabine in the springtime? Think again. Follow this guide to all the specks, reds, and flounder you can handle.

When work or play calls for AC power on your boat or tow vehicle, an inverter is usually the simplest and least-expensive way to provide it. Just plug the inverter into a cigarette lighter or accessory power socket and then plug your AC tools or toys into the inverter.

Portable AC power can also come from a small gasoline generator, but an inverter is silent, exhaust-free and small enough to fit in a glove box. Inverters also have no oil or spark plugs to change, no carburetors to adjust and gasoline never goes bad in its tank between uses.

Little 50-watt models can typically run computer equipment, a mini television set with up to a five-inch screen, a four-head VCR, a 20-watt glue gun or a small power tool (one item at a time, not all at once). They can also recharge the batteries of most power tools or cell phones.

Inverters with a 150-watt output can operate a 100-watt halogen work light, and those with a 300-watt rating can handle a 19-inch color television.

Most inverters are designed to deliver more than their rated output for brief periods so they can handle the extra startup load of an electric motor, but they aren’t designed to carry the extra burden for long. Best results come from choosing an inverter with a watt output rating one and a half to two times the constant output that your AC equipment will use.

Most inverters automatically shut down if the DC input voltage rises above about 15 volts or falls below about 10 volts, if the inverter’s internal temperature gets too high or if the continuous power draw from the inverter is above its design limit.

A safety fuse may be built into the cigarette lighter plug on some inverters, so it’s important not to cut off the plug and wire the inverter directly to a battery. Some 300-watt inverters have a hard-wiring kit available that’s recommended for constant use with appliances that draw more than about half the inverter’s rated capacity.

On the down side, the battery chargers for some tools, flashlights, video cameras and computers don’t work well when powered by an inverter. Monitor the inverter’s case temperature for the first 10 minutes of powering a battery charger, and shut it down if it gets unusually warm.

Small inverters put out power in what’s called a modified sine wave that some highly sensitive electronic devices object to. You probably won’t have any trouble, but if a battery charger, variable-speed power tool or computer printer doesn’t work normally it probably isn’t compatible and shouldn’t be powered by the inverter.

Some high-frequency inverters produce enough electromagnetic interference to be heard on radios and seen on a fish finder’s screen. It isn’t likely that you’ll be using power tools or watching TV while talking on the radio or watching a fish finder, but if you get interference just shut down the inverter while using the radio or sounder.

Inverters are not sealed and must be protected from moisture and hazardous fumes. Keep them dry with enough open space around them for cooling air to circulate freely.

The length of time that an AC appliance will run depends upon how much power it draws and how much reserve your battery has.

The West Marine catalog offers a neat formula for figuring running time. Watt-hours divided by 10 gives you the approximate number of amp hours an appliance draws from your battery. If a device is rated at 20 watts, it uses 20 watts in an hour’s time and is said to consume 20 watt-hours of power. Divide that by 10 and you see that it pulls two amp hours from a battery in an hour’s time. If your battery has a capacity of 100 amp hours, it will run the device for about 50 hours.

By the way, deep-cycle batteries are more suitable for inverters than cranking batteries, especially if you’re a long way from shore.

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