How To Choose An Air-cooled Diesel Generator

Step-by-Step Selection Guide

1. List & Categorize All Loads

· Resistive Loads: Convert energy directly to heat/light (e.g., incandescent lights, heaters, kettles). Running Watts = Rated Watts.

· Inductive Loads: Contain electric motors (e.g., pumps, compressors, power tools). Require a high startup surge (starting Watts).

2. Calculate Total Running Watts

Sum the rated wattage of all devices that will run simultaneously.

· Formula: Total Running W = Sum of all (Resistive Load W + Inductive Load Rated W)

3. Calculate Maximum Starting Watts

Identify the single inductive load with the largest startup surge and calculate the total power needed at that moment.

· Starting Surge: Typically 3x to 5x the motor's rated wattage for direct-on-line startup.

· Formula: Max Starting W = (Total Running W - Largest Motor's Running W) + (Largest Motor's Running W x Starting Multiplier)

4. Select the Generator

Use your calculations to choose a unit with adequate capacity.

· Rated Power (Running Watts): The generator's continuous power output must exceed your Total Running Watts. A 20-30% buffer is recommended.

· Max/Surge Power (Starting Watts): The generator's maximum short-term power output must exceed your Max Starting Watts.

Example Summary:

· Running Loads: 2kW (Heat) + 1.5kW (Water Pump) = 3.5kW

· Largest Motor: Water Pump (1.5kW) with 4x surge = 6kW

· Max Starting Scenario: (3.5kW - 1.5kW) + 6kW = 8kW

· Generator Required: Choose a unit with a Rated Power > 3.5kW and a Max/Surge Power > 8kW. A 5kW-6kW (rated) model is often suitable.

Key Principle: The generator must be sized to handle the largest startup surge, not just the sum of the running loads.