Battery breaker sizing calculator

A battery breaker sizing calculator is a tool used to determine the correct size of a circuit breaker or fuse that is needed to protect a battery bank from overcharging or over-discharging. Here is a simple calculator you can use:

Battery Breaker Sizing Calculator

Inputs:

1. Battery Capacity (Ah): The total capacity of the battery bank in Ampere-hours (Ah).
2. Charge Current (A): The maximum charge current in Amperes (A) that the battery bank can handle.
3. Discharge Current (A): The maximum discharge current in Amperes (A) that the battery bank can handle.
4. Voltage (V): The nominal voltage of the battery bank in Volts (V).
5. Inverter Efficiency (%): The efficiency of the inverter or charger that is connected to the battery bank.

Calculations:

1. Maximum Charge Current (A): Calculate the maximum charge current by dividing the battery capacity by the charge time. For example, if the battery capacity is 200 Ah and the charge time is 8 hours, the maximum charge current would be 200 Ah / 8 hours = 25 A.
2. Maximum Discharge Current (A): Calculate the maximum discharge current by dividing the battery capacity by the discharge time. For example, if the battery capacity is 200 Ah and the discharge time is 4 hours, the maximum discharge current would be 200 Ah / 4 hours = 50 A.
3. Total Current (A): Calculate the total current by adding the maximum charge current and maximum discharge current. For example, if the maximum charge current is 25 A and the maximum discharge current is 50 A, the total current would be 25 A + 50 A = 75 A.
4. Breaker Size (A): Calculate the breaker size by multiplying the total current by a safety factor. A common safety factor is 1.25, which means the breaker size should be 1.25 times the total current. For example, if the total current is 75 A, the breaker size would be 75 A x 1.25 = 93.75 A.

Example:

• Battery Capacity: 200 Ah
• Charge Current: 25 A
• Discharge Current: 50 A
• Voltage: 12 V
• Inverter Efficiency: 90%

Calculations:

1. Maximum Charge Current: 25 A
2. Maximum Discharge Current: 50 A
3. Total Current: 25 A + 50 A = 75 A
4. Breaker Size: 75 A x 1.25 = 93.75 A

Result:

The recommended breaker size is 93.75 A.

Note:

• This calculator is a simplified tool and should not be used as the sole means of determining the correct breaker size. It is recommended to consult with a qualified electrician or engineer to ensure the correct breaker size is used for your specific application.
• The breaker size should also take into account other factors such as the battery bank's internal resistance, the inverter's efficiency, and the system's overall design.