Opportunity / Fast Charge
Partial State of Charging (PSoC), often referred to as Opportunity, Rapid and Fast Charging, has revolutionized the way electric lift truck fleets are managed. Valuable warehouse space and personnel no longer need to be dedicated to battery rooms with spare battery storage, battery handling and changing equipment. Lift truck operators do not need to travel from their work area to the battery room to change out batteries, saving thousands of dollars in lost productivity. Batteries weighing thousands of pounds no longer need to be hoisted in and out of lift trucks, reducing the potential for employee injuries.
Traditional thinking in the motive power battery industry has been to size a lift truck battery for an application to allow for one “cycle” per day, defined as 8 hours of work (discharge), 8 hours of charging, and 8 hours of rest or cool down time. Standard motive power battery warranties limit a battery’s use to one cycle per day. Standard 8-hour charge time allowances have been based on charging rates of about 14-20 amps for every 100 ampere-hours (AHs) of a battery’s rated 6-hour capacity. The practice of PSoC allows a battery to be put on charge many times during a shift or work day which allows one battery to remain in the lift truck much longer than the traditional 8 hour shift with the goal of completely eliminating the need to change out spent batteries during the shift day. Depending on the power demands of the application, enough charge can be applied to a battery during breaks and lift truck downtimes to allow a battery to last two or more shifts.
Opportunity charging typically refers to applying charge rates up to 25 amps per 100 AH of the battery’s rated capacity, while fast or rapid charging refers to applying charge rates between 25 and 50 amps per 100 AH of the battery’s rated capacity. An evaluation of a workday’s duty cycle and available charge times should be performed to determine which type of PSoC is practical for each application. Since a battery exhibits the highest resistance to charge acceptance after reaching 80% of it’s rated capacity, special PSoC profiles are used to minimize heat created by this charge resistance by stopping a charge when the battery reaches 80% recharge levels. Even with a PSoC profile, fast charging rates applied to batteries designed to only accept standard charge rates will cause excessive battery heat. Fast charging enhances thermal issues because there may not be time for the traditional 8-hour cool down time and the batteries are typically kept in an enclosed lift truck compartment during charge allowing for minimal ambient cooling. Excessive battery heat needs to be managed both by using smart charging techniques, but also with battery designs that will address higher heat and throughput levels in order to provide acceptable battery cycle life.
Liftech and EnerSys offer free analysis of your lift truck fleet operations to determine if PSoC can help you eliminate battery changing from your workday. PSoC is especially effective for operations considering changing their fleet’s power source from fossil fuels to electric batteries.
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