What is the difference between modified, pure sine wave inverters?

There are three major types of sine inverters – pure sine wave (or “true” sine wave), modified sine wave (actually a modified square wave) and square wave. Each of these types of inverters serves a particular purpose for your electrical needs and should be used according to that purpose. The various types of inverters range in price and effectiveness, with true pure sine wave inverters topping the chart and square wave inverters existing as the simplest. For more inverter info and specifications on each type, read our brief descriptions below.

Pure Sine Wave: A pure sine wave is what you get from your local utility company and from some pure sine generators (most generators are not pure sine).

• A major advantage of a pure sine wave inverter is that all of the equipment which is sold on the market is designed for a pure sine wave. This guarantees that the equipment will work to its full specifications.
• One of the disadvantages of a pure sine wave inverter is that these are the most expensive of the inverter designs. Still, they outperform all other types of inverters, regardless of use.

What devices need a pure sine wave to function?

• Some appliances, such as motors and microwave ovens will only produce full output with pure sine wave power, meaning that a pure sine wave inverter is an important choice for optimal performance.
• A few appliances, such as bread makers, light dimmers and some battery chargers require a pure sine wave to work at all, making this type of an inverter a mandatory purchase.
• Audio equipment, satellite systems and video equipment will run properly using pure sine wave inverters.

Analog Pure Sine Wave: The sine wave produced by an analog pure sine wave inverter is very similar to that of the digital pure sine wave inverter. The key difference is that the analog switching causes noise or static on the AC wave, meaning that devices powered by an analog pure sine wave inverter will perform at full power but will produce negative results at full power.

• Generally, most appliances, motors, microwaves, chargers and power tools will produce full power and not cause any buzzing or negative effects.
• These types of pure sine inverters are not recommended for medical equipment unless manufacturer approved.
• Use this inverter for electric shavers and emergency flashlights, garage door openers, laser printers and large strobes used in photography

Modified Sine Wave (quasi-sine): A modified sine wave inverter, or quasi-sine wave inverter, actually has a waveform more like a square wave but with an extra step. A modified sine wave inverter will work fine with most equipment, although the efficiency or power of the equipment will be reduced with some. Due to the modified sine wave inverter’s construction, these inverters are often more affordable than their pure sine wave counterparts. These types of inverters may be the optimal solution for larger projects that require less efficient power.

• Motors, such as refrigerator motors, pumps, fans, etc., will use more power from the inverter due to lower efficiency. Most motors will use about 20% more power. This is because a fair percentage of a modified sine wave is higher frequencies – that is, not 60 Hz – so the motors cannot use it.
• Some fluorescent lights will not operate quite as bright, and some may buzz or make annoying humming noises.
• Appliances with electronic timers and/or digital clocks will often not operate correctly. Many appliances get their timing from the peak of the line power – basically, the modified sine has a flat top rather than a peak – this may cause the occasional double trigger. Because the modified sine wave is noisier and rougher than a pure sine wave, clocks and timers may run faster or not work at all.
• Items such as bread makers and light dimmers may not work at all – in many cases appliances that use electronic temperature controls will not control. The most common is on such things as variable speed drills will only have two speeds – on and off.
• Most equipment will operate without any noticeable difference, and because the lower cost, that makes this the most common inverter sold and generally the only type found at your local retailer. Always double-check to be sure whether or not your equipment requires more power or efficiency before choosing a modified sine wave inverter.

Square Wave: What is a square wave inverter? Square wave inverters are the simplest of all inverter types. Only the very cheapest inverters anymore are square wave due to their limitations. A square wave inverter will run simple things like tools with universal motors with no problem – but not much else. These are seldom seen anymore except in the very cheap or very old ones. The Inverter Store doesn’t sell square wave inverters due to their cheap design and lack of benefits.

If you’re unsure whether to use a pure sine wave vs. modified sine wave inverter, or if you have further questions about the types of inverters and their benefits for your projects, you can talk to one of our specialists to help you understand and figure out the ideal type for your solution. Or, take advantage of our pre-assembled kits that combine an inverter with matching accessories, effectively taking the guesswork out of your project.

Choosing the right type of inverter is only one part of the process when creating your off-grid power system. The Inverter Store has many helpful tips for creating the optimal systems, from general information about sine wave inverters and finding the proper inverter size to the difference in battery systems and how to connect your batteries in parallel.