When your golf car batteries don’t seem to last as long on a full charge as they used to, it doesn’t necessarily mean it’s time to replace the entire battery pack. If you’ve been diligent at performing routine maintenance on your batteries, you should also take a look at how they are charged.
Many golf car owners have a charger that they’ve used for years and simply plug it into the battery pack. Proper charging, however, is not as simple as that. Battery manufacturers recommend using a properly sized charger for the amp-hour capacity of the batteries. There are also specific charge algorithms for batteries that control the voltage, current and time during charging to ensure the batteries are fully charged at the end of the charging cycle.
Most modern electric vehicle chargers use a 3-stage charge algorithm. This typically consists of a bulk charge stage that should have a maximum charge current of approximately 10 percent of the 20 hour capacity of the batteries, an absorption charge that applies a constant voltage charge to the battery until the current decreases to ~3 percent of its amp-hour capacity, and the finish charge stage that should have a charge current of approximately 3 percent of the 20 hour capacity of the batteries until the charge is terminated automatically. Additionally, the voltage output of the charger should be sized to the number of cells connected in series in the battery pack.
While your charger may have all the right functions, one of the most common problems is that owners fail to properly size the charger output to the amp-hour capacity of their batteries. For example, a charger designed to recharge a single 12 volt RV battery may not properly charge a battery pack with two 6 volt golf car batteries. To find out if you’re charging your batteries correctly, first look at the battery manufacturer’s charging recommendations for your particular battery. It should have a chart that shows the three-stage charging recommended voltage, current and charge time in hours for your particular battery type.
Elements of a Three-Stage Charge
For lead-acid batteries, the nominal charger voltage is the number of cells connected in series times 2 volts per cell. For example, a battery pack with 24 cells connected in series should use a 48 volt charger. The charger should also have the capability of providing an on-charge voltage of at least 2.6 volts per cell so a 48 volt charger should be capable of providing at least 62.4 volts at full charge to completely charge a 48 volt battery pack.
The charge algorithm used by the charger for a particular type and brand of battery determines how the charger applies the 3-stage profile to properly charge the battery pack without significantly overcharging or undercharging over the life of the battery. During the bulk charge stage, a properly sized charger will return approximately 80 percent of the amp-hours removed on the previous discharge within 4-8 hours depending on how deeply the battery was discharged. During the absorption charge stage, the charge current slowly decreases until 100 percent of the amp-hours removed on the previous discharge are returned; usually within 1-3 hours.
Even though 100 percent of the discharged amp-hours have been returned, the battery is not fully charged. Because of charge efficiency losses, the battery must be overcharged to reach a full state of charge. The amount of overcharge required is dependent upon many factors such as battery chemistry (FLA, AGM, or GEL), battery temperature, battery type and manufacturer, and battery age and condition. This is also the primary reason for selecting the proper charge algorithm or charge profile for the battery being charged. The finish charge stage is designed to provide the proper amount of overcharge to fully charge the battery without overheating and potentially damaging the battery. A properly sized charger should be capable of fully charging a discharged battery within 8-12 hours.
Float and Equalization Charging
Some chargers may also have a float charge and an equalization charge setting. Once the battery is fully charged, a float charge setting can be used to maintain the battery at a full charge state by off-setting the normal self-discharge rate. Similarly, an equalization charge setting should be used on a monthly basis to provide an additional amount of overcharge to prevent stratification and sulfation. Periodic equalization charging balances the cells connected in series to prevent sulfation and provides sufficient gassing to fully mix the electrolyte to prevent electrolyte stratification. The frequency of equalization charging should be based on the application and the frequency and depth of discharges. Since the batteries should already be fully charged at the end of the 3-stage charge, float and equalization charges are not considered one of the charge stages in a 3-stage charge regime. They are considered charge maintenance steps.
As with any electrical device, battery chargers can malfunction or deteriorate over time. It is important to check the battery charger for proper function regularly but, in particular, any time battery performance is observed to be declining. Decreasing battery performance can be caused by a charger that is not performing a proper charge profile. There is a charger diagnostic procedure on the U.S. Battery website that can be used to determine if poor battery performance is caused by underperforming batteries or an underperforming charger. Batteries that are not fully charged on a regular basis will suffer from progressive capacity loss and sulfation.
Taking the appropriate steps to properly charge your lead-acid deep cycle batteries is one step in helping to extend their service life. This, combined with limiting the depth of discharge (DOD) to 50 percent or less through the use of opportunity charging, will maximize the performance and life of your lead-acid battery pack.
If you’re not sure if your charger is up to the task, contact the battery manufacturer and ask what charging algorithm is best for your particular batteries. Additional information on charger diagnostics, battery maintenance, and ways to increase battery efficiency and service life can be found on the U.S. Battery website at www.usbattery.com.
