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Different types of charging technologies

Lead acid batteries


The lead acid battery was the first rechargeable battery used commercially, and it is still widely used today in cars, forklifts and other systems that require large sources of power, and when the weight of the battery isn’t a concern.

Since the mid-1970s, two types of lead acid batteries have been developed. The smaller of the two is the sealed lead acid (SLA) battery, and the larger is the valve-regulated lead acid (VRLA) battery.

Because of their unique design, SLA and VRLA batteries can never be charged to their full potential. These batteries hold the liquid electrolyte in separate enclosures, and contain safety valves for venting when the battery is being charged and discharged. These features make SLA and VRLA batteries virtually maintenance-free. However, because excess charging would cause gassing and water depletion, SLA and VRLA batteries are designed with a lower over-voltage potential.

Absorbed glass mat (agm) batteries

An AGM battery is a type of VLRA battery. It has a fiberglass mesh between the battery plates. It contains the electrolyte, holding it in place as opposed to having the lead freely flood the plates. This makes the battery virtually spill-proof, and ideal for operations that don’t have access to battery-maintenance services. The sealed, maintenance-free design has strongly mounted plates that are not susceptible to shock and vibrations.

The difference between forklift batteries and car batteries

The inexpensive, easy-to-manufacture technology of lead-acid batteries makes them ideal for both cars and forklifts.

Forklifts often use VRLA batteries – including AGM batteries – that can’t be serviced, because they are “sealed”. On the other hand, cars use “flooded-cell type” batteries that can leak and do require some maintenance.

Car batteries are designed to provide high load for a short amount of time, and then they need to be recharged. A car battery won’t sustain the same long draw as a forklift battery.

The power in a forklift battery can be sustained for a long time with a medium load, and then requires a full charge when it’s done. A car battery doesn’t need a full charge, and although it will provide a lot of power, it won’t go as long as a forklift battery.

Conventional charging

Charging a forklift battery overnight for 8-10 hours to achieve a full charge is known as conventional charging. This process always involves charging the battery to 100 percent for whatever its state of charge may be. Hydrogen, an explosive gas, is produced when a lead acid battery is charged. This “gassing” as it’s typically called, can be a safety issue in large battery rooms. When a large number of batteries are being charged at one time, an air circulation system may be required to remove hydrogen from the battery room.

Conventional charging doesn’t charge the battery at the same rate over the full eight hours. It will charge the battery faster over the first four to five hours, and then turn the amperage down and run another few hours to level off the battery.

When you have the time at the end of a shift to charge the battery for eight hours, conventional charging is preferred over fast or opportunity charging. Charging heats up a battery, so another six to eight hours are required for the battery to cool down to room temperature before it can be used. This charging method will give you the longest battery life. It’s good for one-shift operations where the battery doesn’t need to be changed. It’s also used in very high throughput, multiple-shift applications when fast charging or opportunity charging are not good options. Two- or three-shift operations using conventional charging will need two or three batteries per truck respectively so batteries can be used in a lift truck while other batteries are charging and cooling down.

Fast charging

Forklift batteries take as little as 50 percent less time to charge than it takes to charge a battery conventionally in fast-charge technology. A fast charge will charge a battery in two to four hours. Fast chargers work quickly because they don’t turn down the rate of current the way a conventional charger does. These chargers keep the charge rate high during the whole charge time. Gassing is increased due to the higher constant charge rate and increased temperatures. An equalize charge once a week will help balance the sulfating that occurs during charge cycles.

Using a fast charger, productivity is improved since the battery doesn’t need to be charged for eight hours at a time – they can effectively work all day, every day, though the lifespan of the fast charged battery may be shorter. These chargers also reduce the need for multiple batteries – one battery works for one truck with one charger.

Operations that have back-to-back shifts and want their operators to use the same equipment are good candidates for fast chargers. When downtime means lost productivity, fast chargers help keep things moving along.

Opportunity charging

Opportunity charging is a system that allows forklift batteries to be charged during breaks, lunch, between shifts or whenever there is an “opportunity”. An opportunity charger works in the same manner a fast charger does, as it charges the battery to 80-percent state of charge during each charge, and then up to 100 percent after a recommended cool down period. Like the fast charger, it works at a high rate of current, but the opportunity charger shuts off at the 80-percent state of charge and allows the battery to cool down. A fast charger, on the other hand, will continue charging up to 100 percent if left to do so. The opportunity charger charges at a higher current than the fast charger initially, so it reaches its base charge faster.

Like the fast charger, the opportunity charger has the advantage of reducing the need to change batteries during shifts or even between shifts. That gives you the advantage of longer shift operations. However, even when the time is available, these batteries won’t charge at greater than 80 percent like a fast charge battery will, so an extra hour during the day of charging time won’t give you additional power on your battery.

The opportunity charger is best suited for operations that have multiple shifts and limited time for battery charging throughout the day.

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