Knowledge is power when installing, using inverters

Truck drivers have been using AC/DC inverters for a couple of decades now. They are versatile devices and must-haves in any sleeper cab. You’d think, after all that time, drivers and technicians would have figured out how to install and use them properly.

Each year, however, we hear of several truck fires related to improper inverter installation or use. Some vehicles are completely consumed in those fires. This is no laughing matter.

To put it into perspective, a fully loaded 1,800-watt invertor can draw between 150 and 200 DC amps from the truck's batteries/alternator (1,800 watts is about the same as a single 20-amp circuit found in homes). Those are usually peak loads, and the high current draw may not last more than a few minutes, but that can be enough to do some damage.

Light loads

The limits of off-the-shelf inverters

Most small, off-the-shelf inverters — such as those you might find at popular trucker stores — are suitable for light loads and moderate use. The problems crop up when they are tasked with higher loads than they were designed for.

A 450-watt inverter that plugs into a 12-volt power port would be good for charging laptops and tablets, powering a flat-screen TV and maybe a small coffee maker, but not much more. It's not necessarily the inverter's fault, either. You can draw only so much current through a 12-volt port until those pesky fuses or circuit breakers blow.

The answer is not higher-rated fuses, it's lowering demand on the inverter. Try convincing drivers of that while they are cooking dinner in an electric skillet that won't stay hot. Using over-rated fuses or breakers could cause the wires powering the 12-volt outlet to become hotter than the skillet. And that's when things get exciting.

Small, plug-in inverters have limited application. Trying to overload them or bypassing the built-in protection or onboard circuit protection can end badly. They are generally fairly inexpensive, which is what makes them popular. But they are inexpensive because they are low-wattage and may not have the internal protections needed to prevent fires. And they may not have been tested and approved by the likes of Underwriters Laboratories (look for the UL 458 mark on the product) or CSA in Canada.

"You can buy UL-approved inverters that plug into 12-volt power-ports but they will be smaller and more expensive than the non-certified products," says Don (DJ) Hasler, strategic account manager at Xantrex. "The problem we see most often is drivers buying an inverter that is way too big for the power they can get out of that 12-volt port. Drivers will wire-up their own 12-volt connector and plug in a 1,000-watt inverter to power a skillet and then things can go south.

"To stay safe, use the correct invertor for the load, don't overload the inverter, connect it properly using the correct gauge wire and don't bypass the circuit protection," he adds.

That much juice flowing through wiring that's too thin or not securely connected can cause it to become extremely hot because of the additional resistance. And it's hot enough to melt the insulation from wires or cause any adjacent flammable material to combust.

Not long ago, many fleets prohibited drivers from installing inverters in their trucks because of the risk of draining the batteries, resulting in no-starts in the morning, and the risk of fire. Drivers were known to jerry-rig their inverters, often using alligator clips to connect directly to the batteries, but with too small a wire gauge. That sometimes resulted in damaged batteries, damaged appliances, and even fires.

Many fleets soon realized it was in their best interest to install their own inverters or order trucks with inverters right from the factory rather than trying to prohibit drivers from doing so.

"If you buy direct from an OEM you’ll have the benefit of UL certification," says Xantrex strategic account manager Don (DJ) Hasler. "That's the first box the factory checks. And of course, engineering gets involved to make sure the correct sized cabling is used on the AC and the DC side, along with the proper-sized breakers and circuit protection. In other words, it's installed properly."

The downside to an OE-installed inverter is usually the price tag. Hasler says the OEMs usually offer top-of-the-line models with features like DC charging and shore power plug-ins. When plugged into shore power, not only can you run your hotel loads, it also charges the batteries.

"Every fleet would want that," he says. "It makes your batteries last so much longer and it keeps the truck from auto-starting to charge the batteries. The problem is, shore power still isn't there yet in 2020. Since 90% of fleets can't reap the benefits of shore power, they don't want to pay for a Cadillac invertor with a bunch of features they can't use."

As a consequence, many fleets now install their own invertors. They can pick the product they feel is right for the application and have skilled and trained technicians install the devices. But there's still some risk of techs taking shortcuts, like not routing the cable correctly or using the wrong gauge of wire.

"Make sure proper polarity is observed between the battery and inverter DC input," cautions Keith Randolph, field application engineer with Eaton's eMobility controls and power conversion division. "Wiring connections must be snug, as loose connections may overheat due to high resistance and even lead to risk of fire if not properly circuit-protected."

Cable length and routing is also a concern. Longer cable runs increase the voltage drop and add resistance to the circuit. Try to place the inverter as close to the batteries as safe and practical, all things considered, and check technical data on cable length, gauge, and voltage drop to insure the losses are minimal.

"Improper wire undersize or improper circuit protection can lead to equipment failure and even possible circuit fire," Randolph says. "Wiring must be routed securely and clear of any sharp edges or extreme heat, such as when routing through the cab floor and under the cab when near the heat of the engine or exhaust systems."

Hasler says that while the batteries and inverter may not be that far apart, by the time you route the cabling through the floor, around the various corners, and keep it protected from heat and corrosion, the cable run can get pretty long. "That's where the correct cable sizing becomes important," he says. "It's probably going to be longer than you’d first expect."

You can minimize problems by starting with the correct product for the task. Make sure the inverter you select meets or exceeds SAE J1455, UL 458 standards for electrical integrity and vibration.

"A truck application is a harsh environment compared to a stationary environment that many inverters are designed for," cautions Randolph. "Non-approved inverters may initially cost less, but they can increase maintenance costs and can create safety hazards, including potential fires."

To prevent overloading and to optimize performance, determine how the inverter will be used, what devices it will power, and what the duty cycles will be. It is important to size the inverter for the power output that the intended AC loads require on a continuous basis, and for any necessary start-up surge requirement.

Inverters produce different types of AC waveforms. The two most common types of waveforms are true sine wave and modified sine wave. True sine wave inverters produce an AC waveform that is almost identical to the waveform found in your home.

In certain applications, true sine wave inverters are required due to the compatibility requirements of the AC device to be powered — such as radios, amplifiers, CPAP machines, some televisions, some microwaves, and variable speed motors such as drills. As well, Some ground fault circuit interrupt (GFCI) devices may not operate properly off a modified sine wave inverter.

Inverters that operate at higher efficiencies will draw less current from the batteries, and will run cooler compared with lower-efficiency-rated inverters. Inverter efficiency ratings typically range from 75-90%.

All those factors will determine how well the product will work in its intended environment, and it all starts with selecting the proper device and installing it carefully and correctly.

Hasler says Xantrex has manuals and installation videos online to help with the installation, and they even have teams that will install fleet orders.

"There's some cost involved whether you have your own techs do it, or have an expert do it for you," says Hasler. "In the end, there some value in the peace of mind that comes from having it done right the first time."

To the uninformed consumer, an inverter may just be a fancy-colored box with a few wires and a couple of plugs on it. But the uninformed consumer may not realize that the $79 1,000-watt inverter from Amazon can't deliver everything they want and could even cause some serious problems.

"The bottom line is that electrical systems are complicated and careful product selection and professional/trained installation is always recommended to ensure safety," says Randolph.

Jim Park was a CDL driver and owner-operator from 1978 until 1998, when he began his second career as a trucking journalist. During that career transition, he hosted an overnight radio show on a Hamilton, Ontario radio station and later went on to anchor the trucking news in SiriusXM's Road Dog Trucking channel. Jim is a regular contributor to Today's Trucking and Trucknews.com, and produces Focus On and On the Spot test drive videos.

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