Opportunity Charging Lithium-Ion Batteries

Extending out the workday for battery-powered forklifts can be achieved through a trick known as opportunity charging. This allows a battery to be charged a number of times during a work cycle of eight hours. A warehouse that uses this trick can be assured that one battery can remain in a forklift much longer than common. The point is to end the need to change spent batteries during a shift. The procedure allows a forklift operator to sufficiently charge a battery during downtime. If one practices this scheme, a battery can last two or more shifts depending on the power demands of the task the lift is being used to achieve.

Why opportunity charge? Well, warehouse space and workers are able to pursue other tasks and there is no longer a need for a dedicated battery room, spare battery storage, battery-handling and battery-changing equipment along with the personnel needed to do the exchanges. Travel time is also reduced from a work site to a battery charging room. As a result, there is the opportunity to improve productivity and reduce the risk of injuries when lifting heavy batteries in and out of a lift.

In opportunity charging, charge rates are applied of up to 25 amps per 100-ampere hours of the battery’s rated capacity. Fast or rapid charging occurs during which the applied charge rate is between 25 and 50 amps per 100-ampere hours of the battery’s rated capacity.

The process limits a battery’s use to one cycle per day.

Opportunity charging can be performed on lead acid and lithium-ion batteries. The process can be used on all types of handling equipment including small pallet jacks, four-wheel forklifts, and large turret trucks.

Charging Lithium-Ion Batteries

A constant current/constant voltage (CC/CV) charge regimen is commonly used to charge a Lithium-Ion battery. A common characteristic of all Lithium-Ion batteries is that when they’re connected to a charger, the battery efficiently accepts the power and increases its state of charge. It doesn’t matter whether the battery was connected to the charger for 15 minutes of two hours. It will immediately discharge. There is no need for a cooling period for a Lithium-Ion battery after charging.

A lithium ion battery.
(Courtesy: KUBT at flickr.com)

Although a Lithium-Ion battery has several different chemical alternatives, the most commonly used to power materials handling equipment is Lithium Iron Phosphate (LFP).

The difference of LFP chemistry compared to other Lithium-Ion battery alternatives is the long cycle life of about 2,000-4,000 cycles to reach 80 percent of the original capacity, the high power capabilities for charge and discharge, and the lower energy/density than other Lithium-Ion battery alternatives.

Because of its long cycle life, an LFP Lithium-Ion battery can be put into and remain in a lift until it’s retired. There is no need for battery swaps. Moreover, since LFP chemistry can accommodate high power delivered to and from the battery, an exhausted LFP battery can accept a full charge in an hour. The charge doesn’t have to be administered in one charging session. It can be given throughout the shift when the lift’s operator has downtime. Thus, Lithium-Ion batteries are the best battery for opportunity charging.

(Source: forkliftaction.com)