Introduction
Fast charging of industrial batteries has become a main stream charging technology due to the operational savings, increased productivity and safety that this technology offers. Many users have made the switch away from conventional charging in the past ten to fifteen years as the benefits of fast charging are realized at manufacturing plants and distribution centers throughout the United States, Canada, and Europe.
History
Fast charging was introduced in the 1970s with a focus on NiCad batteries for handheld products. By the early 1990s, fast charging was being developed for on-road electric vehicles (EVs) as a way to reduce charge time and make highway travel with EVs a reality. But with very little EV market potential in the mid to late 1990s, the fast charging concept became a feasible option for industrial use, providing power to lead acid batteries used in industrial forklift truck batteries, automated guided vehicles (AGVs) and other motive electric vehicles. Although fast charging was met with strong skepticism at first, the technology has proven to be practical and cost-effective.
From Conventional to Fast Charging
What is conventional charging?
Conventional charging supplies a battery with power at a very low rate, taking 8-10 hours to fully recharge the battery (a fully charged battery is considered to be at a 100% state-of-charge, or SOC). For this reason, conventional charging is best suited for one-shift operations. In one day, such an operation would require a battery to charge over an 8-10 hour period, rest and cool down for another 6-8 hours and be put to use (discharged) over an 8 hour shift.
For multi-shift operations, conventional charging can be used, but is not ideal. A 3-shift operation would require the purchase of 3 batteries per forklift, rather than one. In one day, a forklift would continuously operate, pausing only to switch out batteries rotating between charge, discharge and cool down every 8 or so hours. This means batteries must be changed 3 times a day, requiring labor, time and risk of injury to workers. Not only that, but conventional charging works by charging the battery to a 100% SOC every day. This causes a process called gassing, which refers to the release of highly flammable hydrogen and oxygen gasses. In order to maintain hydrogen concentrations at safe levels and below OSHA limits, warehouses and distribution centers must dedicate valuable floor space to centralized charging rooms.
How does fast charging compare?
Fast charging supplies a battery with power at a very high rate and at every possible opportunity. This includes breaks within and in-between shifts, as well as lunch breaks. Due to higher charging rates and more frequent charging throughout the day, fast charging requires only a single battery per truck. This eliminates the need for and cost of additional batteries used in conventional charging applications. Risk for injury that would occur during battery changes is significantly reduced—if not eliminated all together—and forklift driver productivity greatly improves.
Adding to the benefits of fast charging, batteries are never charged over 85% SOC on a daily basis. This eliminates any unnecessary gassing. The battery is required, however, to reach 100% SOC at least once a week, which is normally done on weekends when less workers will be affected by gassing.
Benefits of Fast Charging
Return on Investment (ROI)
ROI and Net Present Value (NPV) of fast charging in two and three shift operations well exceed the return requirements of the most aggressive finance managers. Although the up front cost of fast charging equipment is higher than that of conventional chargers, significant operational savings as well as initial investment savings can be realized.
Consider the case of a manufacturing facility planning to acquire (or upgrade to) a forklift truck fleet of 50 trucks. With conventional charging, assuming a ratio of 2.2 batteries per truck, 120 batteries are needed versus only 50 batteries with fast charging. In addition, with conventional charging, battery extraction and changing equipment will also be needed to change batteries between shifts. The charts below compare the initial investment costs and operational savings of conventional versus fast charging:
