Fast charging is similar to opportunity charging in that the battery is plugged into the charger during breaks and in between shifts. The start rate of the charger can be up to 60% of the battery’s total rated amps per hour. State of charge for the battery will hover between 30% and 80% during the day. Standard batteries cannot be fast charged; there are specific batteries that have been designed to handle the increased amperage and have been outfitted with double cables.
In contrast to conventional charging where the battery is used until it reaches 20% state of charge and then recharged for 8 hours, opportunity charging is a frequent volley of usage and quick charges during breaks and shift changes. Operators do not change batteries during shifts, and instead repeatedly plug the battery into charge when the truck is not being used. State of charge for the battery remains between 30% and 80% during the day. To get the most out of these short charging windows, the charger is designed to deliver a higher rate of charge. The start rate for opportunity chargers is up to 30% of the battery’s rated amps per hour.
All temperatures are corrected to 77 degrees Fahrenheit. Below that temperature, the specific gravity and thus the voltage of the cells reads falsely higher than it really is. Modern day chargers detect the voltage of the battery, adjusting their output and shutting off accordingly. In cold storage, since the voltages read higher than they actually are, the charger sees a fully charged battery and shuts off before the battery is actually fully charged. This results in a battery that never gets fully charged before the next shift and keeps getting run lower and lower.
Conventional chargers follow a cadence of: discharge battery 80% of total capacity. Charge for 8 hours. Allow battery to cool for 8 hours. In general, the start rate of the charger delivers about 15% - 20% of the battery’s total amps per hour. The charge curve then tapers off to a finish rate of delivering approximately 5% of the battery’s total rated amps per hour.
Before adding or replacing chargers, it is important to know whether your electrical supply is single phase or three phase, and whether the AC voltage is 208, 240, or 480. Additionally, look at the corresponding maximum rated amp draw listed on the charger’s nameplate to make sure you won’t be blowing fuses when you power up the charger.
Equalize charge is an important maintenance step to do at least once every two weeks. Over the course of usage, the different cells in the battery become somewhat imbalanced with some being more charged than others. If left to continue unchecked, minor imbalances can become big problems. Equalize charge takes care of this problem by continuing a slow trickle charge for several hours after the normal charge process has completed.