Q&A with Steve Carlson

Power inverters convert standard battery (DC) power to AC household power. Depending upon whom you ask, that’s to the delight or chagrin of fleet and maintenance managers, who often have a love/hate relationship with inverters.

With that definition in mind, let’s get started:

Why Is There A Love/Hate Relationship With Inverters?

Inverters have always been a magnet of controversy. Fleets know that drivers love them, as they provide an extra measure of creature comfort—who wouldn’t want to plug in their devices like they do at home? But fleet managers can be nervous about inverters and their potential to damage the truck’s electrical system.

Still, I’m seeing the distrust of inverters really becoming a thing of the past, if, and I stress if, the right inverter and installation practices are followed. Inverters can be a great asset to drivers and fleets. The key is for fleets to do their homework and know what’s best for their operation prior to making a purchase. One size does not fit all and inverter quality varies greatly.

What Size Inverter Should A Fleet Or Owner-Operator Buy?

It’s easy to say get the biggest inverter on the market and you’ll be covered for all your needs. But that’s not the best advice. Sizes range from 300-watt cigarette lighter plug-in inverters to 5,000-watt units. Fleets or owner-operators should do surveys on truck size and power usage and understand how they will use an inverter—what items they want powered and what items will be used at the same time. That will help size the right inverter for their operations.

As an example, a driver will often run a microwave, TV, and laptop all at the same time. On each device, you’ll see a wattage number. A microwave might be rated at 1,000 watts, a TV at 250 watts, and a laptop at 95. Add them up to see how much continuous power you’ll need and then add 20 percent. So, in this case you’ll need just over 1,600 watts. Next, round up to find an inverter that meets your power needs. Xantrex, for example, offers an 1,800-watt unit, and that’s what we would recommend.

What About Surge Power?

Yes, you’ll have to consider that as well. While determining continuous power is important, don’t forget the power you’ll need for surge.

Whenever you power up any device, the initial load is more—and sometimes double—what the continuous power requirement is. So the surge rating on quality inverters should be about double. An 1,800-watt inverter can handle a short 3,600-watt power surge requirement.

You also need to see how long the inverter can handle the surge—the longer the better. Some inverters on the market can handle only a few milliseconds of surge before the power draw shuts down the inverter. Others can last five seconds or more, and that’s what buyers should look for.

What’s The Difference Between A Sine And Modified Sine Wave Inverter?

Both work well in a truck environment, but for those running sensitive electronics (like CPAP machines) or products that are plugged into their own chargers—a drill or a toothbrush—means a sine wave should be the preferred choice. Sine wave is the same power as what you get at home, meaning the voltage is consistent without spikes or drops. The device you’re powering reacts just as it would if you were plugged in at home.

You have to pay a little more for that premium power monitoring and it’s worth it to protect your sensitive equipment. However, if you’re powering run of the mill electronics and appliances, modified sine wave power is just fine.

OK. How Much Is The Premium For Sine Wave? And Is Performance The Same?

The price gap has narrowed and today most higher-wattage sine wave inverters cost 15 to 20 percent more than a modified inverter.

With a sine wave unit, you’ll notice a slight decrease in the efficiency rating since electronics within the inverter use power to keep electrical levels consistent. It’s not much—we have an 87 percent efficiency rating on a Xantrex sine wave unit compared to 92 percent on a modified inverter. Here’s a good analogy: It’s like the difference between running a 6-cylinder car versus 4-cylinder car. That 4-cylinder car may get a bit better fuel economy, but the 6-cylinder is better in overall performance.

Is It OK For A Fleet Or Driver To Install The Inverter?

Generally speaking, yes for a fleet, no for an owner operator. Most fleet technicians will have no problem handling installation, and Xantrex does offer fleet training programs to our customers. We certainly would recommend our training program if there are any questions on installation.

But, just remember, you’re working with electricity and electricity can bite if you’re not careful. It’s our recommendation that inverters over 300 watts feature hard-wiring and fusing.

There is also a bevy of things to consider when installing an inverter, starting with where it should go and whether there is adequate ventilation to allow heat to dissipate. You also have to be cognizant of wire sizing and the distance between the inverter and plug-ins which can be put in the sleeper; plus the distance between the battery and inverter.

Most fleets and owner-operators want the convenience of a factory-installed and warranted inverter. We really recommend either an OEM-install when you purchase a new truck or to have the installation done by an authorized dealer. The OEMs have installation down to a science and it’s done on the line to rigid specs. Truck and aftermarket dealers also have the experience, so it’s worth spending a few extra bucks to have the installation done right, the first time, should a fleet’s own staff not have the time or expertise.

What Kind Of Reliability Can A Buyer Expect?

When it comes to reliability, the old adage that you get what you pay for comes into play. That may seem like a trite saying, but boy is it ever true in our category.

Buyers will pay more for an inverter that has a "Regulatory Listed" approval such as UL or ETL with UL458 rating. This means the inverter was inspected and approved by an independent agency, which safeguards against issues with electricity. UL458 is the listing for inverters and chargers in mobile applications. They must meet strict vibration, environmental, and thermal requirements that non-UL458 units do not.

This is the most important safety point I can make, and in fact, TMC's RP163 calls out this UL listing for all inverters and chargers installed in a truck. What’s more, TMC’s RP160 that discusses DC and AC wiring in a truck has requirements that are automatically met by UL458 listed inverters. The main point being that the neutral and ground are bonded together within the inverter. Inverters that are not UL458 listed do not do this as it allows the inverter to be made at a much lower cost.

Beware of an inverter that is not Regulatory Listed. We’ve seen these types of products actually shock users, plus internally they often can’t protect themselves against power surges.

It goes without saying, but I’ll say it anyway: inverters installed by truck manufacturers all are UL approved, but many inverters sold at truck stops are not.

I Assume You Test And Validate Inverters To The Nth Degree

You bet we do. We feel we have to. We’re dealing with an electrical product and if things go wrong, they really go wrong. We don’t want that. Buyers don’t want that. Inverters that have been tested will last longer versus inverters from manufacturers that don’t spend the time and money to ensure quality. A quality inverter should last well beyond its warranty period.

But, again, not all manufacturers have the same philosophy because testing and validation costs money. A quick way to figure out if they do test/validate is to see if they are promoting that fact in their marketing material, or on their web site.

What About Automatic Shutdowns On Inverters?

Inverters will occasionally shut down, but quality inverters do so without damaging themselves. If dust or hair, for instance, gets inside the inverter, it can cause it to overheat. A higher-watt Xantrex inverter, for example, has an error code that lets you know what the problem is—in this case it will tell you that you are overheating and to check the fan. A simple cleaning will correct the problem and you’ll be back up and running. Other inverters could leave you guessing as to what the problem is.

If you overload the inverter, placing more wattage demands on the inverter than it can handle, the inverter will shut down. The difference between a quality inverter and low-end inverter is how they deal with a shut down. A quality inverter is designed to shut down with no ill effects. A low-end inverter can wear out after multiple overloads.

Should A Buyer Get An Inverter With A Battery Charger?

The simple answer is yes if you can use shore power (electrical outlets at home or on the road at terminals, loading docks, or truckstops). When plugged in, you can run everything you’re running with your inverter for as long as you want, plus you can recharge and top off your batteries. The more you can use shore power, the better, as it prolongs the life of your batteries.

In fact, having the shore power option and a charger in the system will add 20 to 30 percent to the life of the batteries if plugged into grid power whenever possible. It also has the potential to eliminate one battery swap out over five to six years’ use of the truck. This happens by keeping batteries fully charged, offsetting parasitic loads, and reducing the number of cycles.

I find that most installations use the inverter off the truck’s starting batteries and quality inverters will have a low voltage disconnect (LVD) to shut down when voltage drops to 11.7 volts. This ensures the truck will have enough juice to start.

I always recommend to buyers that they check on the LVD feature before they buy an inverter. If they don’t have one in the inverter, or on the truck, an inverter can run the batteries down to 10.5 volts, or below. That’s not good. Sure, it lets drivers run electrical devices longer in the cab and sleeper. But, guess what? They won’t be able to start the truck. And, it’s why we always recommend the inverter, or truck, comes equipped with its own LVD.

What About Adding Batteries To Run Longer?

That’s a great option and one we often recommend. It can make sense to run two dedicated deep-cycle batteries and connect them to the inverter. Yes, they do add weight to the vehicle, and add cost. But, deep-cycle batteries were designed to be drawn down to a 50 percent state of charge, or 10.5 volts. This gives double to triple the amount of continuous power to run hotel loads. Something drivers will appreciate.

For A Fleet, What If They Allow Drivers To Bring In Their Own Inverters?

Not knowing what kind of inverter a driver is bringing in is why fleets often have a policy of not allowing drivers to outfit company trucks with their own inverters.

But, if they do allow it, we recommend fleets give them a list of approved devices, with the most important common denominator being UL458 listed. And we suggest fleets makes it mandatory that their own shop or an outside dealer does the installation.

What Is The Purpose Of An Inverter If A Fuel-Fired APU Is Already Being Used?

The addition of an inverter to a truck’s electrical system will reduce hours of use on a diesel-fired APU—assuming that the APU does not already have shore power compatibility. And, it will reduce maintenance costs and increase APU life. An inverter can be used for hotel loads in the cab as long as environmental conditions do not require air conditioning. When those conditions happen, the operator can just power up the APU for air conditioning.

With this set-up, the only time the APU would need to come on is if the batteries drop to a low level. Once the batteries are charged, the APU can shut off again. This significant reduction in APU run time means a quick payback on the cost of the inverter.