Generator Load Calculator

In this guide

Step-by-Step User Guide

1. Enter Your Equipment Details

Initial Row: By default, the table has one row ready to fill.
Equipment (1st column): Type a short description, e.g., “Pump #1” or “Fan #2.”
Load Type (2nd column):
- Hover over the “?” to see the meanings:
  - DOL – Direct On-Line
  - SD – Star–Delta
  - SS – Soft Starter
  - VSD – Variable Speed Drive
  - STD – Standard non-motor load
- Choose the load type that matches your equipment’s starting method.
Locked Rotor Amps (LRA) (3rd column):
- If the motor specifies a known LRA, enter it here. The calculator assumes 9 s at LRA if non-zero.
Start Current (SC) (4th column):
- If LRA = 0, the tool uses SC for motor startup logic (e.g., 9 s for DOL, partial voltage for Star–Delta, etc.).
Full Load Current (FLC) (5th column):
- Enter the running current at normal load.
Start Time (6th column):
- Enter the second (from 1 to 30) when this equipment starts.
- If you put 0, it means the item never runs (or is off).
Action (7th column):
- The “X” button removes the row if you decide you don’t need that equipment.

Tip for Mobile Users: If you’re on a phone, scroll sideways to see all columns. The table is horizontally scrollable to prevent cramped text.

2. Add or Remove Rows

Add Equipment: If you have more than one item, click the “Add Equipment” button. This inserts a new row with the same columns (Load Type, LRA, etc.).
Remove: To delete a row, click “X” in the Action column. The row disappears immediately.

3. Calculate the Load

After you fill in all necessary fields:

Click “Calculate.”
The page displays two main sections:
- Input Summary: A table listing all equipment, load types, LRA, SC, FLC, and start times.
- Load Calculation:
  - Time 1–15 seconds
  - Time 16–30 seconds
In each time range, you’ll see:
- Total Load (A) row for each second $T 1, T 2, \dots$ .
- Total kVA row, converting amps to kVA under 3-phase, 400 V assumptions.

The highest load column(s) will be highlighted in pink (and bold) so you can quickly spot peak demand.

4. Adjust Inputs if Needed

If the total load looks off or you forgot an item, simply edit any row or add/remove rows.
Click “Calculate” again to refresh the summary and load calculation.
The results will update immediately on-screen.

5. Export a PDF Report

Scroll down to “Generate PDF Report.” You’ll see the following fields:

Project: e.g., “New School Project.”
Date: your current date or relevant project date.
Revision: versioning note, e.g., “Rev A.”
Generator Description: short description or notes about the generator or job specs.

Then:

Click “Export as PDF.”
The tool will generate a PDF file and open it in a new browser tab.

PDF Contents:

Your project info (Project, Date, Revision, Generator Description)
Input Summary and Load Calculation tables in landscape format

6. Review or Print the PDF

From the new tab, you can save or print the PDF.
Your form data remains intact in the original tab, so you can switch back, change something, and export again if needed.

7. Mobile Usage Tips

The calculator is responsive.
On smaller screens (portrait mode), horizontally scroll to see all columns.
The text fields and dropdowns expand to full width, making them easier to tap.
The “X” remove button is in the last column, so you might need to swipe sideways to see it.

8. Finished!

Your generator load calculation is done.
Return anytime to modify or recalculate with updated parameters.
Keep in mind local electrical codes and design standards – this tool is not a substitute for professional engineering review.

Motor-Starting Logic Under the Hood

Wondering how this calculator gets its results?

We’ve built in formulas that replicate each motor’s realistic and unique startup behaviour:

DOL (Direct On-Line) motors can draw full Locked Rotor Amps for about 9-13 seconds before settling to full-load current. (we used 9s)
Star–Delta starters smoothly transition from ~30–35% of starting current, dip briefly during phase switching, and then ramp up to full load.
Soft Starters reduces voltage during start-up, leading to a gradual torque increase but a steeper current profile than a VSD. At the start, the current is 1× FLA. Every second, it increases linearly. It ramps up to 2.5× FLA over ssRampTime (5s).
Variable Speed Drives gradually ramp both voltage and frequency, reaches 1.2–1.5× full load current (FLC) during this phase. Steady-State (After 5–10s). Once the motor reaches the target speed, the current drops to running current unless there are sudden load variations.
Standard (Non-Motor) Loads assume a constant current draw from the moment they switch on.

load profiles each formula mimics actual load behaviour during startup. That means more accurate load profiles and a better handle on generator sizing - all automatically, so you can focus on selecting the right equipment instead of crunching numbers.

How to use: