DC Velocity - August 2018

Mat er i a l H a nd l i n g

CHA RGI NG SY S TE M S

SPEEDING UP THE PROCESS

In a nutshell, opportunity and fast charging speed up the battery charging process. Along the way, they also help eliminate some of the labor and maintenance associated with conventional charging.

For most of battery history, conventional charging was the only way to charge a lead-acid lift truck battery. Simply put, with conventional charging, a facility has one or more batteries that are “changed out” when they are drained of power—that is, they are removed from the lift truck and connected to a charging system. The batteries are charged for eight hours, cooled for eight hours, and then put back into use. The process requires a designated battery space where charging and other maintenance activities are performed. Depending on the operation, the process could take up considerable real estate inside a warehouse or DC—not to mention the time and effort needed for the change-out process, and the need for multiple batteries for heavy-use and/or multiple-shift operations.

“That was the traditional way we did it up until 15 years
ago,” Harrison explains. “Then, some smart people said,
‘Let’s recharge faster so we don’t have to take [the battery]
out of the truck.’”
The result was opportunity charging, which is done
throughout the workday when the lift truck is not in
use—during lunchtime and other short breaks, for exam-
ple. With opportunity charging, the battery remains in
the lift truck and is plugged into a charger; larger facilities
often have banks of charging stations for this purpose.
Maintenance is reduced—no more changing, charging, and
cooling of multiple batteries throughout the day. Instead,
maintenance is performed weekly and monthly, including
a regular equalize charge.

But the story doesn’t end there. “Then, [researchers]
said, ‘Let’s increase the rate so we can charge it even faster,”
Harrison says. “And now we have fast charging.”
Like opportunity charging, fast charging is done through-
out the day, without removing the battery from the lift
truck. The key difference between the two methods is the
start rate when charging the battery; start rate refers to the
amount of current you’re putting back into the battery at
the start of the charge. As Harrison explains, charging hap-
pens on a curve, with the most current going in at the start
before tapering off and ending at about a 5-percent rate.
Speeding up the charging process happens at the beginning
of that cycle. Quite simply, fast charging utilizes a faster
start rate, further accelerating the charging process so that
you get even more use out of your equipment per shift.

As an example, consider a 1,000 amp-hour battery. The start rate for conventional charging is about 20 percent, meaning that you’re putting 200 DC amps back into that battery at the start of the charge. The start rate for oppor-

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