Quick Answer
Wiring batteries in parallel poses risks due to potential unequal voltage drops, charge imbalances, and BMS communication challenges, leading to battery degradation, reduced lifespan, or even catastrophic failures.
Understanding Parallel Battery Schemes
When wiring batteries in parallel, it’s essential to consider the voltage drop across each battery, as unequal voltage drops can lead to charge imbalances. For example, with 12V batteries, a 1-ohm resistance in one of the battery connections can cause a 12-millivolt voltage drop, which translates to a significant difference in charge over time. To mitigate this, use the same battery type, ensure proper connection and cable sizing, and monitor voltage drops to prevent unequal charging.
Battery Management System (BMS) Considerations
When using a BMS to manage parallel battery banks, ensure the BMS can handle the increased complexity of parallel connections. Ideally, the BMS should be designed to manage multiple parallel strings, and it should be able to communicate with each battery in the string. In a parallel configuration with 4 batteries, a BMS with a communication protocol that can handle 4-6 parallel strings would be necessary to maintain accurate state-of-charge (SOC) tracking and prevent overcharging.
Interconnect Sizing and Cable Requirements
Proper interconnect sizing is critical to prevent voltage drops and ensure efficient energy transfer. When calculating interconnect size, use the total battery bank current (in amps) and the maximum allowed voltage drop (in volts) to determine the required wire gauge. For example, for a 400Ah/24V battery bank with a 2% maximum voltage drop, the interconnect size would need to support 10.67A (400Ah x 24V / 0.02). Use the American Wire Gauge (AWG) table to select the correct wire size based on the calculated ampacity.
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