Calculating Battery Life for a 12V Device with Parallel Batteries and a Voltage Regulator

When dealing with multiple batteries and a voltage regulator to power a device, it is crucial to understand how to calculate the device's run time. This article will guide you through the process using different configurations and considerations.

Parallel Configuration with a Voltage Regulator

Suppose you have four 20V Dewalt batteries with a 6Ah capacity each. These batteries are connected in parallel, and a voltage regulator is used to maintain the voltage. Let's break down the calculation:

Calculate Total Ah: 4 x 6Ah 24Ah

Calculate Total Voltage: Each battery has a voltage of 20V, so the total voltage remains 20V.

Calculate Available Power: 24Ah x 20V 480Wh (Watt-hours)

Calculate Load: The device is 85W and the regulator is 85% efficient.

Calculate Run Time: Running time is determined by dividing the available power by the load and the efficiency of the regulator.

Time (480Wh / 85W) x 0.85 4.8 hours or 4 hours and 48 minutes.

Series Configuration with a Voltage Regulator

Alternatively, if the regulators are in series instead of parallel:

Calculate Load Current: The device requires 85W at 12V, so the current is 85W / 12V 7.08A.

Calculate Total Ah from Batteries: 4 x 6Ah 24Ah.

Calculate Run Time: To prevent damaging the batteries, do not use the full capacity. Using 24Ah / 7.08A 3.4 hours. This is a conservative calculation, and the actual run time may be less due to inefficiencies and practical considerations.

Heatsinking the Regulator: The regulator will dissipate nearly 57W, so ensure proper heat sinking to avoid overheating.

Buck Converter Configuration

Utilizing a buck converter, the total stored energy from the batteries is:

Calculate Total Watt-hours: 4 x 20V x 24Ah 480Wh.

Assume Usable Watt-hours: Not fully draining the batteries, assume 400Wh usable.

Calculate Run Time: 400Wh / 85W 4.7 hours.

These examples provide a range of run times based on different configurations. The actual run time may be slightly optimistic due to practical factors such as efficiency and battery characteristics.

Optimizing Battery Life

To optimize the battery life:

Monitor Battery Voltage: Ensure the battery voltage does not drop too low during operation. Use Efficient Components: Choose regulators and converters with high efficiency to minimize power loss. Thermal Management: Implement proper heatsinking for regulators to prevent overheating. Offload Heavy Loads: Distribute the load if possible, such as by connecting additional power supplies or reducing the load on the regulator.

Conclusion

By carefully considering the batteries, voltage regulator, and load, you can determine the optimal run time for your device. The calculations provided here offer a good starting point, but practical factors will also play a significant role in the actual run time.