Freezer Startup Surge Calculator

Check whether an inverter can handle the extra power a freezer compressor needs at startup, with a preliminary pass or caution result.

Your results

The problem this solves

A freezer can run fine on an inverter once it is going, then fail to start. The compressor needs extra power for a moment when it switches on.

How to use it

• Enter how many freezers you have and how many could start at the same time, for example after a power cut.
• Enter the running watts of one freezer.
• Enter the manufacturer starting watts if you have them. If not, use a startup multiplier. This is a rough guess.
• Add any other appliances running together, then your inverter's continuous and surge ratings.

The formulas

• Startup demand per freezer = starting watts, or running watts × multiplier
• Peak demand = freezers starting × startup demand + other running load
• Running load = all running watts added together

Reading the result

• Likely not enough: peak demand is above the surge rating, or running load is above the continuous rating.
• Caution: you use more than 80% of either rating, which leaves little margin.
• Preliminary pass: both are below that, based on the numbers you entered.

Worked example (illustrative)

Two 150 W freezers start together with a 4× multiplier. Each needs about 600 W, so the peak is 1,200 W. The running load is 300 W.

On an inverter rated 1,000 W continuous and 2,000 W surge, that is a preliminary pass.

Limits

A multiplier is a rough estimate. If the inverter is rated in VA, check the datasheet for the watts figure. Also check how long the surge rating lasts.

This is a planning aid, not an electrical design. Ask a qualified installer to verify.

Related

• Inverter and Battery Sizing calculator plans the battery side.
• Freezer Power Rating calculator helps you find the running watts.
• Generator Cost per kWh calculator compares backup options.

FAQ

Why does a freezer need more power to start?

The compressor motor draws a short burst of extra current as it begins to turn.

Where do I find the starting watts?

Look in the freezer manual or ask the manufacturer. Some inverter makers also publish surge guidance.

What if two freezers start together?

Their startup demands add up. Staggering them, if you can, lowers the peak.

Results are estimates, not professional advice. See our disclaimer. Calculator and guide by Borniventure Ugochukwu Nwakamma.

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