Pure vs modified sine wave generators

 

Pure sine wave generators

A synchronous generator where an engine turns a magnetic rotor within a stator with wires wound through a steel core produces a True Sinewave. A USA domestic HSB or portable synchronous generator (2 pole rotor) will govern the rotor speed to 3600 RPM to maintain 60 Hz (60 cycles in one second). The rotation of the rotor induces alternating current and voltage in the stator windings that rise and fall as both magnetic pole positions change.



A Pure Sine Wave provides more efficient power and minimal interference. This helps to reduce audible and electrical noise in fans, fluorescent lights, audio amplifiers, TV, fax, and answering machines. This does not directly correlate to Total Harmonic Distortion (THD). Find more information about THD in the What Is Total Harmonic Distortion (THD)? article. 
 

Which Generac generators produce a pure sine wave?

All of Generac's home standby generators, such as the Guardian series, produce a Pure (True) Sine Wave with precision engineering that uses the engine to turn a magnetic rotor within a stator with wires wound through a steel core.

Modified sine wave generators (inverters)

An inverter generator rotates many permanent magnets about a fixed stator of windings that induce a 3-phase alternating current and voltage similar to Figure above (x 3). However, that output is fed into an inverter module within the generator that rectifies that power into Direct Current and then inverts the power to a synthetically produced sinewave.

Over 20 years ago some of the first inverter generators used basic technology and the sinewave created either a “square wave” or ‘modified sinewave”. This caused some issues with common devices like televisions and microwave ovens. More recent inverter generators produce a synthetic sinewave that meets utility-grade specifications and looks like a synchronously produced sine wave.

Modified sine wave generators are just as safe for electronics as true pure sine wave generators, in some cases having an even lower THD.

 

Which Generac generators have a modified sine wave?

Note that this list is not exhaustive:
 

• XT series generators such as the 8000 EFI and 8500 EFI
• XC series generators
• GP 3500 IO
  • Note: The GP3500 IO is unique here. Most GP series generators do not have an inverter so they do not have a THD safe for sensitive electronics. 
• Any portable generator that features an inverter.
• Battery power stations will have a pure sine wave, although these do not draw power from a combustion engine.

Total harmonic distortion (THD)

Total Harmonic Distortion is a measure of how “clean” the output power is.  The waveform can show noise or deviations from the geometric shape due to various factors. Home standby requirement is less than 5% THD according to UL2200. 

A GP6500 with a lower-cost alternator measures 20% at rated load and a HomeLink 6500 may measure 5% THD at rated load because of the alternator design and resultant cost.

Since an inverter is producing the sinewave synthetically and the technology has grown more sophisticated over the years, 5% THD is now standard in Generac inverter generators.