Despite electrics’ growing popularity (currently, they represent about 70% of new lift truck sales in the U.S.), users do encounter some drawbacks. One is that operators must drive to a charging station that’s compatible with the battery on their truck; if those chargers are located far from work areas, operators may end up spending almost as much time traveling as they do charging. Another is the cost of upgrading electrical service to accommodate chargers, not to mention the long waits for local utilities to bring in the necessary lines to facilities that don’t already have them.
There is a way to get around both of those issues, though: chargers that are located inside the lift truck and can be plugged into an ordinary 120v or 240v AC electrical outlet. But while on-board chargers can be a cost-effective, practical alternative in certain applications, they do come with potential drawbacks and trade-offs.
CONVENIENT BUT SLOW
With onboard charging, there’s no need to travel to a charging station or a battery room; instead, operators can partially or fully charge the battery at almost any location with a standard wall outlet, notes Mike Brown, director, energy solutions, at Mitsubishi Logisnext Americas, which includes UniCarriers and Jungheinrich, among other lift truck brands. (The location must safely accommodate the parked trucks without interfering with foot and vehicle traffic, of course.)
There are two main types of cables with onboard chargers: the AC (input) side and the DC (output) side, explains Bryan Norris, applications manager at Stryten Energy, a provider of batteries and charging systems. The AC cable plugs into a 120v 15-amp wall receptacle like those typically found in homes. The DC cable plugs into the battery. To charge the battery, an operator turns off the lift truck, disconnects the battery connector from the lift truck, and plugs the battery into the charger. The operator then plugs the AC cable from the charger into the wall outlet.
The convenience of being able to charge almost anywhere facilitates partial charges, but it takes a long time to get a full charge. A 110v or 120v single-phase outlet, like those commonly seen in homes and offices, will produce a slow, gradual “trickle charge” of 1.2 to 1.4 kW, while a 240v single-phase outlet, like those used for large home appliances, will generate a charge of four to six kW, Brown observes. “If you’re running the truck eight hours a day and have 16 hours after that to charge, then you’ll be able to charge most batteries up to full or nearly full operating status” with a 120v plug, he says. With 240v, a battery often can recharge in eight hours or less, depending on its size.
For that reason, on-board charging is most appropriate for one- or two-shift operations where an overnight period is available for charging, says John Pizarro, senior product manager, electric counterbalance, with lift truck manufacturer Linde Material Handling, a unit of Kion Group. A three-shift, continuous operation simply will not have the time available for a lengthy charging session.
On-board chargers have long been common and even standard in Class III walkie pallet trucks and stackers. That’s because their batteries are small, they typically are used only a few hours a day, and they often travel throughout the warehouse, with less predictable deployments than large forklifts used for other applications. However, some forklift OEMs, such as Hyster, Big Joe, and Linde, are now offering on-board chargers on Class I sit-down counterbalanced and (in a few cases) Class II narrow-aisle forklifts.
The larger trucks with their bigger batteries require an overnight or weekend to fully charge, according to Bill Pedriana, president of forklift maker Noblelift. A truck with an on-board charger can still use an external one, so in busy environments, a fleet might want to consider a 480v three-phase external charger to get a faster full charge and use on-board charging to “top up,” particularly for lithium-ion batteries that “are happy with a mid-range charge,” he says.
LEAD-ACID OR LITHIUM?
Different on-board chargers on the market are intended for use with a range of power sources, including 120v and 240v AC single-phase outlets with 15 amperage, Norris says. Some are designed for certain sizes and types of lead-acid batteries. For example, The Raymond Corp. has partnered with battery maker EnerSys to offer on-board charging for thin-plate pure lead (TPPL) batteries, which do not require watering or weekly equalization (a process that entails intentionally overcharging a battery to remove sulfate buildup and balance the voltage across all cells), in certain models of its walkie pallet trucks and walkie straddle stackers. Stryten Energy’s offerings include chargers paired with sealed, low-maintenance absorbed glass-mat (AGM) batteries, and with flooded tubular-plate batteries, which perform well with a partial charge.
With lead-acid, however, partial charges may not be ideal. “Lead-acid batteries don’t like being on and off charge; they like being fully charged from a low depth of discharge,” Pedriana observes. “Those short breaks won’t charge the battery much and will eventually cause deterioration issues.” Trevor Bonifas, general manager, motive power group, for Crown Equipment Corp., notes that while the small lead-acid batteries in Class III trucks can be on-board charged at a standard 120v outlet, that setup would not provide enough current to properly charge and maintain larger lead-acid batteries.
Lithium-based batteries have been a catalyst for the shift from internal combustion (IC) engine trucks to electric-powered trucks, and a growing number of on-board chargers are specifically designed for them. One reason on-board charging works well with lithium batteries, according to charging solutions provider Delta-Q Technologies, is that lithium packs have a greater energy density than lead-acid batteries do. That means more energy capacity can be delivered in substantially less space, opening up room in the lift truck for a charger. Another reason is that a lithium battery can charge anywhere within a facility where there is a 120v or 110v outlet with a 15- or 20-amp circuit, Bonifas says. “That’s primarily because lithium doesn’t need gassing or the kind of maintenance that lead-acid does.”
What’s more, “lithium-ion likes to be charged often and fast, which is perfect for heavier operations where opportunity or fast charging is needed,” says Martin Boyd, chief marketing officer for lift truck maker Big Joe. But on-board charging a lithium-ion battery at a slower rate can in many cases satisfy those lower-intensity applications where there is sufficient idle time between shifts or operations while still providing flexibility and convenience, he says.
THE ELECTRICITY FACTOR
Simplicity and convenience may be the most obvious reasons to adopt on-board charging, but there are other reasons a fleet would want to charge forklift batteries from a wall outlet instead of a conventional charger.
For one thing, on-board charging technology can be a practical alternative for facilities with limited electrical infrastructure. External chargers run on a 480v three-phase system and must be installed by a certified electrician, Boyd says. Plus, some facilities might have to upgrade their electrical service to safely accommodate them. On-board charging, by contrast, eliminates the need for expensive upgrades—one of the primary reasons it’s so attractive to facilities that rely on short- and medium-term rentals that have extensive idle time between operations.
For another, high-output external chargers consume a lot of energy, so in some buildings, fast or opportunity charging a large number of forklifts at lunchtime might require more energy than the electrical infrastructure can deliver. With “grid-friendly” on-board charging, Pizarro says, “you can solve [problems] with equipment rather than by changing the building, which is costly and often a permanent decision.” (Pedriana, though, cautions that the electric bill for multiple forklifts drawing power from standard outlets over many hours could be higher than one might expect.)
To help determine whether on-board charging is appropriate for a particular application, Boyd recommends working with an authorized forklift dealer to arrange a demonstration that includes an overnight slow charge for a forklift used in normal operations. Data from the forklift’s battery management system tracks how a battery is being used, how much power it is delivering, when it is being charged, and, importantly, when it is not being charged. That information, he says, “is foundational in ensuring the proper battery sizing and determining whether the on-board charger sufficiently meets the demands of the application.” A demo can also be an effective way for fleets that are considering switching from IC to electric trucks, allowing them to “test drive” battery-powered equipment even if their facility doesn’t have high-speed, three-phase charging stations, he adds.
It’s worth keeping in mind that on-board chargers are subject to the same vibrations, shocks, moisture, temperatures, and dirt that the forklift encounters. So it’s important that they be tested for those conditions, Norris of Stryten Energy advises; he says his company’s chargers meet Ingress Protection (IP) 66 standards for keeping out water and other fluids, dust, and debris. The chargers also withstand vibration in compliance with a standard developed by General Motors. For heavy-duty, dirty, and other challenging environments, though, it might be best to use external chargers, says Logisnext’s Brown.
Opinions regarding retrofitting trucks with on-board chargers are mixed. Three of the OEMs we spoke to for this article—Big Joe, Mitsubishi Logisnext, and Noblelift—only offer factory-installed on-board chargers on original equipment. Crown’s Bonifas and Linde’s Pizarro say their companies do some retrofitting, but on a case-by-case basis, and only by an authorized dealer.
But all agree that there are reasons to be cautious. For one thing, Pedriana says, the truck may not have been designed with the space required to properly accommodate the charger. For another, it would be difficult, and perhaps impossible, for a third party to properly integrate the charger with the battery management system—required for lithium-ion batteries—and the forklift’s controller area network (CAN) system, which could lead to safety hazards and unexpected performance errors. Furthermore, a third party would likely not be able to meet some safety requirements, such as preventing the truck from energizing and moving while charging, he adds.
EASIER AND MORE FLEXIBLE
Any decision about batteries and charging solutions will involve additional technical and safety considerations beyond those discussed in this article, so it’s imperative to consult an authorized lift truck dealer, charger manufacturer, or other qualified technical expert before making any moves. It’s also important to note that the experts we spoke with emphasized that the on-board charger, battery, and battery management system should be treated as an integrated solution. Those elements must be tested together to ensure they communicate correctly with each other as well as with the forklift’s electronic control system.
At the end of the day, Brown says, the biggest benefits of on-board charging are that it makes battery charging easier for everybody, creates more flexible applications for customers, and helps solve customers’ problems. With all the ongoing developments in forklift battery and energy technology, he adds, “it’s a great bridge to whatever is coming next.”
Editor’s note: A useful resource for learning more about on-board charging is “The Evolution to Lithium Batteries & On-Board Charging Systems in Lift Trucks,” a white paper from Delta-Q Technologies. It is available for download at https://connect.delta-q.com/lift-truck-evolution-white-paper.
An inside job
If you’re new to the world of on-board charging, you might be wondering where exactly those chargers are located on a forklift truck. It turns out there’s no single answer: The positioning depends on the forklift class and model, the charger’s dimensions, the space available inside the truck, and the type of battery involved, explains Trevor Bonifas, general manager, motive power group, for Crown Equipment Corp.
In Crown’s case, on-board chargers are located inside the cover of the forklift or in the battery space, depending on the model, although a few models can go either way. Big Joe incorporates on-board chargers directly into the chassis of the lithium-ion forklifts in its latest lineup as standard equipment. In Linde’s North American trucks, the charger is attached to a steel frame mounted on top of the battery. Some forklift OEMs work with charger specialists like Delta-Q Technologies to integrate on-board chargers into their trucks, while others, such as Big Joe, design and manufacture their own on-board charger technology.
In some cases, forklift battery makers embed chargers with the batteries. EnerSys, for instance, offers an “all-in-one” unit with a charger positioned on top of its thin-plate pure lead (TPPL) batteries for Class III equipment. Another example is Stryten Energy, which integrates chargers made by one of its partners, Delta-Q, with some of its own batteries. Depending on the forklift model, battery type, and power requirements, Stryten’s chargers are built around the battery, located inside the battery tray, or mounted on top of the battery lid with a protective cover over it, says Applications Manager Bryan Norris. In a standup forklift, for instance, the battery is completely surrounded, so the charger fits best in the battery tray, he explains. But in a walkie rider, the top of the battery is exposed, so there is room to place the charger on top of it.
