A new current

| February 01, 2007

The inverter itself has two cooling fans.

Many truckers purchase small appliances designed for a sleeper cab that run on the 12-volt DC (direct current) that’s in truck batteries. But having 110-volt, AC (alternating current) in the sleeper opens up a world of possibilities. You can then purchase standard, small household appliances that are available everywhere and much less expensive. Also, you can plug in your laptop computer and printer.

Appliances, especially the motor-driven ones, operate a lot more efficiently when using the higher voltage AC, taking less current and using smaller cords. This means less strain on the truck batteries and lower fuel consumption.

We visited K.L. Harring Transportation in Bethel, Pa., where Paul Mitchell, applications engineer of mobile equipment at Xantrex, installed a Xantrex 1800-watt inverter into a new Kenworth W900L. We received the help of Tommy Vajdic, the shop manager, and Robert Reed, technician.

Mitchell first laid out the inverter and wiring, which comes in a premium kit called Cab Power Plus put together by Phillips and Temro. The DC wiring, which carries up to 200 amps, is 2/0 wiring designed for use in welding that has more strands and therefore can carry all that juice with much less resistance and heat than regular battery cable. This gives better voltage to the inverter.

The inverter itself has two cooling fans (A). A cooler inverter works better because its electrical resistance increases with heat. The AC wiring is loomed with a protective, orange plastic cover. The AC wiring connectors have male and female ends and snap together.

The inverter has an internal circuit breaker and ground fault interrupter. Inverters can burn up, says Mitchell, when wiring problems or overload exist, and should carry an Underwriter’s Laboratories safety rating (UL 458) as the Xantrex unit does.

The DC wiring has a 200-amp fuse, critical because a ground in the DC circuit can easily cause a serious fire.

The unit comes with a separate line for shore power. When the driver plugs in, a solid-state internal transfer switch disconnects the batteries and ensures all power is drawn from outside. Although this unit did not have it, an optional feature allows the shore power to feed back into the batteries and charge them up. This unit has a low-voltage cutoff. It operates at 10.5 volts and also has an alarm that warns you voltage is getting low.

The first step for any do-it-yourselfer is to review the safety instructions in the installation manual. Handling the DC battery output is where the greatest risk lies, as it’s always there and grounding a wire could easily start a fire because of the high amps. AC has enough voltage to give you a serious electrical shock.

One way to reduce the risk is to work backward all the way from the receptacles, through the inverter, and then from the inverter toward the batteries. Wait to connect to the positive battery terminal until the rest of the wiring throughout the vehicle is secure, and the fuse is installed and mounted.

Mitchell first laid out the wiring to visualize how it would have to be routed through the truck. Refer to B for the layout. The rear of the inverter is where the DC from the batteries inputs. The front end is where the AC is output.

B also shows that the inverter’s control panel can be popped out and remote mounted with the signals carried through a standard telephone line included in the kit.

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