Calculating Battery Requirement for a 1.5 HP Deep Well Water Pump with an Inverter

Introduction

To power a deep well water pump with a 1.5 horsepower (HP) motor using batteries and an inverter, you need to calculate the necessary battery quantity. This article will guide you through the step-by-step process of determining how many 100 Ah batteries are needed, considering inverter efficiency, and the current draw from the batteries.

Step-by-Step Calculation

1. Convert Horsepower to Watts

A 1.5 HP pump can be converted to watts as follows:

1.5 HP text{Horsepower} × 746 W/HP 1119 Watts

2. Account for Inverter Efficiency

Inverters do not operate at 100% efficiency. A typical inverter efficiency is around 85%. Therefore, the input power required from your batteries can be calculated as follows:

Input Power Output Power ÷ Inverter Efficiency 1119 Watts ÷ 0.85 ≈ 1316 Watts

3. Calculate the Current Draw from the Batteries

Assuming the inverter operates on a 12-volt (V) system, common for battery inverters, the current draw can be calculated using Ohm's Law:

I P ÷ V 1316 W ÷ 12 V ≈ 109.67 Amps

4. Determine Battery Capacity

A 100 Ah battery can supply 100 amps for 1 hour. However, to avoid deep discharging and to prolong battery life, it's better to use only about 50% of the battery capacity. The usable capacity of one 100 Ah battery is approximately 50 Ah.

5. Calculate the Duration One Battery Can Run the Pump

The runtime for one 100 Ah battery at a current draw of 109.67 amps can be calculated as follows:

Runtime hours Usable Capacity ÷ Current Draw 50 Ah ÷ 109.67 A ≈ 0.46 hours or about 27.6 minutes

6. Determine How Many Batteries Are Needed for Desired Runtime

To calculate the number of batteries needed for a specific duration, multiply the current draw by the desired runtime. For example, if you want to run the pump for 2 hours:

Total Ah Needed Current Draw × Desired Runtime 109.67 A × 2 hours 219.34 Ah

Divide the total Ah needed by the usable capacity of one battery to determine the number of batteries required:

Number of Batteries Total Ah Needed ÷ Usable Capacity per Battery 219.34 Ah ÷ 50 Ah/battery ≈ 4.39

Therefore, you would need at least 5 batteries, 100 Ah each, to run a 1.5 HP deep well water pump for approximately 2 hours, accounting for inverter efficiency and battery discharge limits.

Conclusion

Always consider your specific setup and requirements as actual performance can vary based on pump specifications, inverter quality, and battery conditions.