An outlet for charging frustrations
March 01, 2011 - MMH Editorial
We all wish the process of fueling up at the gas pump was a bit speedier, if only to dull the pain of watching dollars trickle away. At least it doesn’t take 16 hours like it does for a lift truck battery to be charged, cooled and sent back to work. In the warehouse, fast-charge and opportunity-charge systems aim to make recharging a battery as convenient as visiting a gas station, and the science behind each technology might even help keep costs down.
Both fast-charge and opportunity-charge systems use decentralized power sources to bring the power to the truck, where the battery stays put. But key differences in infrastructure, charge rates and warehouse rhythm will give each technology advantages depending on the operation.
According to Kenro Okamoto, electric product planning specialist for Toyota Material Handling, the primary difference between fast charging and any other charging technology is the continuous communication between the battery and charger. Conventional chargers, which do not extensively communicate with the battery, use a simple repetitive charging algorithm designed to take the battery to a 100% state of charge. “If you hook a battery up to a conventional charger, that charger is blind,” says Okamoto. “It just runs through the motions and blasts the battery.”
A fast-charging system, however, is constantly adjusting the amperage going into the battery based on its temperature, charge level, and even the electrolyte level in the pack.
“A battery with the exception of the equalization process, is optimally charged between 80% to 85%,” says Okamoto.
No battery should be run below 20%, he adds. A lift truck’s performance will be reduced before a battery gets that low, but Okamoto says that doesn’t stop many operations from running their batteries to the bitter end. “I have seen many applications that have experienced high battery turnover and short battery life. These conditions are usually attributed to operations that continually run their batteries to below a 20% state of charge,” Okamoto says.
Although opportunity charging has minimal battery monitoring capabilities, setups often require fewer up-front installment costs. Fast-charge infrastructure can include electric substations and significant costs.
When speed is essential, the fast-charge setup will boast recharging speeds as much as four times that of conventional systems. According to Okamoto, conventional charging delivers 16 to 18 amps at 100 amp/hours, opportunity charging 25 amps, and fast-charging 40 to 60 amps. Fast-chargers typically use a dual-connector for power delivery, allowing double the power flow.
A fast-charge battery’s inter-cell connectors also use copper as well as lead for enhanced conductivity.
Depending on the rhythm of an operation, fast-charging and opportunity-charging could keep a battery charged at between 25% to 85% at all times, prolonging battery life, increasing uptime, and improving operator productivity. Unlike a trip to the gas station, it’s enough to put a smile on your face.