When multiple batteries are connected in parallel, all positive terminals are joined together, and all negative terminals are connected together. This configuration creates a single, larger battery bank, increasing the total stored energy available for use. The parallel setup is common in applications requiring a specific operating voltage but demanding extended run times or higher power delivery. Examples include large recreational vehicle (RV) power systems, off-grid solar energy storage, and electric vehicle battery packs.
How Parallel Connections Affect Voltage Output
The most fundamental characteristic of a parallel battery connection is that the total output voltage remains the same as the voltage of a single battery. If three identical 12-volt batteries are connected in parallel, the resulting battery bank still provides 12 volts to the connected device. This occurs because the batteries are not stacked end-to-end to increase the electrical potential difference, as happens in a series connection.
Imagine the voltage as water pressure in connected pipes; joining more pipes side-by-side increases the volume available, not the pressure. This setup is chosen when the application requires a fixed voltage, such as a 12-volt appliance, but needs a longer duration of power.
Increasing Capacity and Run Time
Connecting batteries in parallel directly increases the total energy storage capacity, which is measured in Amp-hours (Ah). The capacities of the individual batteries add up to determine the total capacity of the bank. For instance, two 100 Ah batteries connected in parallel create a 200 Ah battery system. This larger capacity means the battery bank can supply current for a significantly longer period, extending the run time of the connected load.
The parallel configuration also reduces the total internal resistance of the battery bank. Internal resistance is an inherent resistance that limits current flow and causes energy loss as heat. By providing multiple parallel paths for current, the effective internal resistance is reduced. This reduction allows the battery bank to deliver higher peak currents more efficiently and minimizes the voltage drop that occurs under heavy loads.
Practical Considerations for Parallel Battery Banks
Setting up a stable and efficient parallel battery bank requires careful attention to the characteristics of the batteries used. It is crucial to use batteries that are matched in type, age, and capacity to prevent internal current imbalances. If batteries with different voltages or capacities are connected, the higher-voltage battery will attempt to charge the lower-voltage one until they equalize. This continuous current flow between batteries can generate excessive heat, reduce efficiency, and shorten the system’s lifespan.
Before connecting batteries, their terminal voltages should be nearly identical, ideally fully charged and allowed to settle for several hours. The physical setup requires proper wiring to ensure effective current sharing among all batteries. Using thick gauge wire and ensuring all connecting cables have the same length helps minimize resistance differences. Unequal resistance can cause uneven charging and discharging across the bank, making a Battery Management System (BMS) necessary in complex systems to monitor and balance the parallel units.