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Connecting Batteries In Series Or Parallel

Electric golf cars are typically powered by several batteries that act as one single power source. The batteries are connected in a configuration that provides the voltage necessary for the golf car’s electric motor to operate correctly.  As an approach to lower battery pack costs, some golf car manufacturers and fleet managers have converted to fewer, higher-voltage batteries with the same overall pack voltage.  Even though this approach is acceptable, it’s important to understand the effects on power and range by first understanding how deep-cycle batteries are connected to provide voltage and capacity before making any changes.

The battery connections within a golf car are dependent upon its motor’s voltage requirements. Most golf cars come from the manufacturer with the batteries connected in series. This results in a battery pack with the same amp-hour capacity as one battery, but the voltage is equal to the sum of all of the batteries combined. For example, two 6-volt 200 Ah batteries connected in series will produce 12-volts at 200 Ah. Battery amp-hour capacity is independent of battery pack voltage but the total energy content of the battery pack is equal to the battery amp-hour capacity times the battery pack voltage.  You can think of energy content as similar to the number of gallons of gas in a car’s gas tank. The more energy, the farther you can drive between charges.

 

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In other applications such as large diesel trucks or recreational vehicles, it’s common to connect deep-cycle batteries in a parallel circuit. This has the opposite effect from batteries connected in series because the total battery voltage remains the same as one battery, but the total amp-hour capacity is now the sum of the batteries in parallel. For example, two 6-volt 200 Ah batteries connected in parallel will result in a pack with 6-volts at 400 Ah.

Batteries In Parallel

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In golf car applications it’s unusual to see batteries connected in parallel, it is common to see fewer, higher voltage batteries connected in series to achieve the required pack voltage. The trend to fewer batteries with higher voltage may seem like a good approach, but keep in mind that higher voltage golf car batteries typically have lower amp-hour capacities than their lower voltage counterparts. For example, a 48-volt golf car can use four 12-volt batteries or six 8-volt batteries. While the total battery pack cost is usually lower for a set of 12-volt batteries, the amp-hour capacity is also lower resulting in lower driving range.  This may also result in shorter battery life from the set of 12-volt batteries. This is due to the deeper discharge on the lower amp-hour capacity set of 12-volt batteries. By using more of the battery’s available amp-hour capacity on each discharge, more active material in the battery is “worked” and the batteries overall lifespan is reduced.

If your course isn’t getting adequate life from your batteries or if the batteries simply aren’t providing enough range, it may be more cost-effective to switch to a higher capacity battery pack with a greater number of lower voltage batteries. This can be done with either six 8-volt batteries or eight 6-volt batteries to provide a 48-volt battery pack with higher amp-hour capacity, higher energy content, and greater driving range. See the chart below for a comparison of relative driving ranges with the three different battery configurations.

If the cost of an unplanned switch to higher capacity batteries is outside of your current budget, it may still be advantageous to replace with similar higher voltage batteries to save initial cost.  However, it is important to replace the batteries with the same amp-hour capacity as the original batteries or higher.  As golf cars age, their energy efficiency decreases and they may require higher amp-hour capacity for the same driving range.

Either way, it is important to make sure your batteries are connected correctly and matched to the vehicles required voltage. If you have any questions regarding series and parallel connections, you can visit http://usbattery.com/info-center/configuration/ to view diagrams for various connection possibilities.

Note:  Some large golf utility vehicles, personnel carriers and off-road vehicles that require even higher energy and power may have battery packs connected in a series-parallel configuration.  This allows them to use a similar 48-volt electric motor as a standard golf car but with a higher amp-hour capacity battery pack to supply their increased power and energy requirements.  Since these series-parallel battery packs can be connected in multiple configurations, owners should consult the vehicles owner’s manual for proper battery connection.  Diagrams of some typical series-parallel configurations are also shown at http://usbattery.com/info-center/configuration/