Generators Resource

Interactive Sizing & Electrical Reference

The Basic Difference

If you are shopping for a portable generator, you will quickly notice that Inverter Generators cost about twice as much as Conventional (Open Frame) Generators for the same amount of watts. Why?

  • Conventional Generator: The engine spins an alternator at exactly 3,600 RPM to mechanically create 120V / 60Hz alternating current (AC).
  • Inverter Generator: The engine produces raw AC, rectifies it to DC, and then uses a microprocessor (the inverter) to synthesize a perfect, clean 120V / 60Hz AC wave electronically.

What is Total Harmonic Distortion (THD)?

The quality of electricity is measured by THD, which represents how "messy" or "jagged" the electrical waveform is.

  • Grid Power (Your house): Less than 3% THD (Very clean).
  • Inverter Generator: Less than 3% THD (Pure sine wave, very clean).
  • Conventional Generator: 10% to 25% THD (Modified, messy sine wave).

Are Conventional Generators Safe for Electronics?

This is the most heavily debated topic in backup power. High THD (messy power) can theoretically cause microprocessors to glitch, overheat, or fail.

If you plug an expensive gaming PC, an OLED TV, or medical equipment directly into a conventional generator, there is a small risk of damage. However, many modern electronics have robust internal power supplies that filter out messy power.

Appliances with AC motors (refrigerators, well pumps, table saws, fans) don't care about THD. They will run perfectly fine on a cheap conventional generator, though they may buzz a bit louder and run slightly hotter.

Inverter vs Conventional Comparison Matrix

Feature Inverter Generator Conventional Generator
Power Quality (THD) < 3% (Safe for all electronics) 10-25% (May harm sensitive tech)
Noise Level Very Quiet (50-60 dB) Very Loud (70-85 dB)
Fuel Efficiency Excellent (Engine throttles down) Poor (Engine always runs 100%)
Weight & Size Compact, lightweight Heavy, bulky steel frame
Price per Watt High ($$$) Low ($)
The Verdict: If you are running job site power tools or a heavy well pump, buy a cheap conventional generator. If you are powering a modern home with smart fridges, TVs, laptops, or RV camping in a quiet park, spend the extra money on an inverter generator.

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