Diagnosing Battery Charger Problems

Undercharging is one of the most common reasons for reduced operating time and overall poor performance of golf cars and other types of electric vehicles that use deep cycle flooded lead-acid batteries. While many golf car operators blame the batteries, the problem can also result from a poorly performing charging system. Keep in mind that battery chargers are subjected to temperature extremes and corrosive environments that can affect their performance over time. So before you replace another set of batteries, try these diagnostic procedures to ensure your charger and charging methods are working properly. 1. Connect the charger and make sure it is on and charging. Test the voltage at the battery pack positive and negative terminals. On-charge voltage will normally continue to increase until the charger terminates the charge automatically. It is important to determine the maximum on-charge voltage and charge current (on the charge meter if available) observed near the end of the charge cycle just before the charge terminates. 2. Once the charger has completed a charge cycle and has automatically turned off, unplug the power to the charger. Wait one to two minutes and reconnect it. The charger should resume charging normally. Note the charge current and the time at the beginning of charge. This is usually described as an ‘equalization charge’ and should continue for at least 30 minutes before checking the charger’s performance. With many chargers, this step can also be performed by unplugging the DC power cord from the charger to the battery pack. If this method is used, confirm that the charger restarts and continues to charge for at least 30 minutes. 3. It’s at this point that you can begin to check the charger’s performance. Check the on-charge voltage at the battery pack’s positive and negative terminals. The voltage will normally continue to increase to the range of 2.50-2.60 volts per cell, until the charge terminates automatically. See Table I to determine the minimum and maximum on-charge voltages for the battery pack based on nominal pack voltage. If the voltage does not increase or initially increases and then decreases, record the following information. a) The maximum and final on-charge voltages. b) Charge current (if available). d) The charging time from the start until it terminates automatically.


Graph Battery On Charge Voltage

4. The next step is to check the on-charge voltage of each battery and compare it to Table II to determine the acceptable Charge Voltage Variation for each battery’s nominal voltage. If the voltage varies beyond the values stated in Table II (either variation from pack average or variation from highest to lowest), replace the lowest voltage battery and repeat the diagnostic test. Test the failed battery separately to determine mode of failure.



Graph Battery On Charge Volt Variation

Armed with this information, you may be able to determine that the charger is not working properly if:

a) Both the on-charge voltage for the battery pack or on-charge voltage for each battery fail to reach the equivalent of 2.5 volts per cell times the number of cells connected in series.

b) The on-charge voltage increases and then decreases (with charger still charging), and if the on-charge voltage of each battery does not vary by more than the values shown in Table II for 6, 8, or 12 volt batteries; either variation from pack average or variation from highest to lowest. c) If the battery pack on-charge voltage reaches the equivalent of 2.60 volts per cell ( the maximum in Table-I), and the charger does not terminate the charge after 1-3 hours. If you found that your charger is not working properly, keep in mind that your batteries may still be good. Flooded lead-acid batteries can be brought back to full capacity with a full charge.

If you decide to purchase a new charger, look for a programmable charger with a selection of multiple charge algorithms. Deep cycle batteries from various battery manufacturers require different charge characteristics to deliver optimum performance and life. Most charger manufacturers provide programmable chargers with selectable charge algorithms designed for each battery manufacturer’s products. Using the battery manufacturer’s recommended charging procedure will optimize battery performance and life of your battery pack.

After you fully charge the batteries with your new charger, you can always take specific gravity readings for each battery with a hydrometer to determine if the battery is at a full state of charge. Several cycles of charging and discharging with the new charger may be required to return the battery pack to peak capacity. For a more detailed version of this charger diagnostic procedure or more information on flooded lead acid batteries or specific gravity readings for batteries, visit www.usbattery.com.