I am planning to purchase a good inverter, and pure sine wave inverters cost about 3 times as much as modified sine wave ones of the same power. I am thinking about a 2000W continuous/4000W peak inverter 12/24VDC -> 230VAC.

Which commonly used equipment requires a pure sine wave, and what kind of equipment will be equally fine with a modified sine wave?

I am especially wondering about compressor and absorption refrigerators, dehumidifiers, electric drills, fans, microwave ovens, common power tools and kitchen tools. Purely electronic, computer and lighting equipment will not be used through this inverter, as these will have dedicated low-voltage DC-DC converters straight from the battery.

Are pure sine wave inverters any more efficient then much cheaper modified sine wave ones, in terms of input battery consumption per 230VAC output power?

Do there exist inverters which can accept a wide range of input DC voltage, for example will work on all of: 12V, 24V and 48V DC?


7 Answers 7


Some people claim that certain loads "may" not work as well, or "may" be damaged, with anything other than a pure sine wave.

Since the power coming out of my wall sockets is significantly different from a pure sinewave, I suspect these sincere and well-meaning people are merely repeating propaganda from the manufacturer of a pure sinewave inverter, much like people repeat urban legends.

There is only one kind of device that I know doesn't work as well with a non-sine-wave inverter: devices that use a "capacitive power supply" -- see How efficient is a capacitive power supply? for details.

Since a "capacitive power supply" has a power factor near 0, it is questionable whether any "capacitive power supply" meets EU-mandated power factor laws, such as EN61000-3-2.

I suspect that all products -- as long as they were designed after EU-mandated power factor laws went into effect -- should work just as well on "modified sine wave" as with "pure sine wave" inverters.

Of course, I can't possibly know about every product ever designed -- if there is any specific product (that was designed after those EU-mandated power factor laws went into effect) that can't work or doesn't work as well with "modified sine wave" power, I would be interested. If anyone can explain why it doesn't work, in enough detail that I can try to avoid that kind of failure, I would be fascinated and grateful.

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    \$\begingroup\$ Devices that use zero crossing circuitry certainly may not work as well or at all, as well as devices with active power factor correction, especially processor based PFC. Digital products may have functional issues with all the additional harmonics introduced onto the line. Not working as well may be subjective. A radio may work but sound like crap with a modified sine wave supply due to the harmonics coupling into the speaker amplifier. The "damage" referred to may be caused by excess heat dissipated in inductive loads and the greater stress on the power supply components and filter. \$\endgroup\$
    – bt2
    Apr 17, 2011 at 15:37
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    \$\begingroup\$ Yes, as I mentioned, some people claim that certain loads "may" not work as well. Can you give any particular examples, as I did, or are you merely repeating an urban legend? \$\endgroup\$
    – davidcary
    Apr 22, 2011 at 1:52
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    \$\begingroup\$ This discusses a real-life Dell laptop AC adapter that was destroyed by a modified sine wave inverter, so it's not just marketing hype. \$\endgroup\$ Jun 13, 2015 at 15:49
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    \$\begingroup\$ There is something of a question of "how pure is pure". Wall outlet power is not a perfect sinewave but it's a lot closer to one than what a "modified sinewave" inverter kicks out. \$\endgroup\$ Dec 12, 2015 at 16:53
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    \$\begingroup\$ 9+ years on :-). I powered an HP laptop supply with a MSW inverter. The 100 Hz noise level was loud and alarming. I assume that they has a large input capacitor that disliked the square wave transitions. I'd not have been surprised if the psu and/or inverter had died early on if we'd continued to use the inverter. \$\endgroup\$
    – Russell McMahon
    Dec 18, 2020 at 5:09

The modified sine wave inverters generally cause more power loss in your products' power supplies. So the inverter itself may not be any more efficient, but the equipment running on a pure sine wave inverter will most likely run more efficiently. This is especially true for inductive loads, such as all the equipment you listed.

I'd guess that most of your equipment with linear AC/DC power supplies will work, but perhaps not as efficiently or with reduced performance and increased heat. Many radios, for example, will sound worse when run off a modified sine wave converter. Other products that use switching supplies may not work. I'd recommend ponying up the extra money for the pure sine wave inverter for anything other than an emergency power supply you need to use temporarily when power is lost, for example. Especially as you are looking to drive inductive loads.

I'm not an expert on inverters, but I know there are plenty that run on 12V designed for the RV community.


Generally speaking, anything with an inductive or motor load, pure sine wave is better. A load that first rectifies the input (PC power supply, phone charger etc) a modified output would be sufficient


Most equipment is likely to work but quite possibly at a lower efficiency. Lower efficiency can lead to overheating. There may also be problems with interference.

Any EMI filter capacitors will experience higher currents than normal. If those capacitors were already marginal then the increase can lead to failure.

Rectifier circuits will likely experience higher peak currents. Again if those components were maginal to start with then the increase can be the difference between survival and failure.


Some kinds of power meters may also not work correctly (or they may be damaged) if they are connected to a modified sine wave source. See an example of a burnt wattmeter here.


ALL switching based supplies that run with an AC input can be run on DC directly, gotta love bridge rectifies and EU laws... I've run everything from motors to "sensitive" medical equipment on modified sine, the only difference between the two is that modified sine wastes more power in the equipment being run. But seeing as how I've run most industrial equipment on modified sine with no problems for days on end I think it's just marketing bull.

  • 3
    \$\begingroup\$ If using a modified sine rather than a sine wave causes a supply that was 90% efficient to instead be 80% efficient, that will cause the supply to generate twice as much heat as it otherwise would. If one has equipment which is temperamental on hot days, using a modified sine wave could easily make the problem at least quantitatively worse. \$\endgroup\$
    – supercat
    Mar 21, 2013 at 16:16
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    \$\begingroup\$ The irony here is that because you are using power supplies designed for industrial and medical equipment (generally the most expensive and most robust of power supply designs) you are not experiencing the many disadvantages which appear at the margins and therefore affect cheaper designs more severely. \$\endgroup\$ Jun 23, 2015 at 6:00
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    \$\begingroup\$ Indeed, the idea that medical equipment is "sensitive" is mostly BS. Medical equipment is generally designed by people who are more interested in proving their products are safe under all sorts of fault condition than in pinching pennies. \$\endgroup\$ Dec 12, 2015 at 17:09

The currently selected answer is quite contentious with good reason. It's implying that Modified Sine Wave (MSW) will just work without describing why it may or may not work. We can attack this problem from a theoretical/mathematical perspective assuming a load "desires" a pure sine wave.

Assuming a load requires a pure sine wave, that would mean that it rejects or can't use all frequency components outside of the main frequency (50hz or 60hz). If we assume the load is purely resistive (to approximate power wasted) and we normalize it, we can integrate a squared sine wave vs a squared square wave vs a squared MSW to compare power using \$P=V^2/R\$.

enter image description here

Two level square wave (-vdd,+vdd)

Integral of sin(x)^2
$$ Ideal =\int_{0}^{\pi}(sin(x))^2 dx= \pi/2$$
$$ Square = \int_{0}^{\pi}1 dx= \pi $$ $$ Wasted\_power = 50\% $$

MSW, transition happens at \$0.5vdd\$ crossing, aka \$30\$ degrees or \$1/6\pi\$ and \$5/6\pi\$ (-vdd, 0, +vdd):

enter image description here $$ Ideal=\int_{\pi/6}^{5/6\pi}(sin(x))^2 dx= 1.480 $$ $$ MSW = \int_{\pi/6}^{5/6\pi}1 dx= 2/3\pi = 2.094 $$ $$Wasted\_power = 29.3\% $$

The main concern here, is that if your system truly desires a sine wave input, you're burning a lot of extra power which has the potential to thermally destroy or pre-maturely age your device/system. If you know your system is designed to handle the dumping of 50% more power if it's a square wave or 30% more power in a 3-step MSW then you're probably safe to use a MSW inverter.

Note that this will also cause torque ripple in A/C motors due to off times followed by a hard application of power which increases noise and vibration on top of the thermal issue.

This is mostly an analysis of inductive loads including motors/compressors/fans/transformers(microwave). Note that in the transformer/microwave case, this will cause the transformer to warm up rather than dumping the extra power into your food.

The other category that the OP discussed are digital electronics requiring switch mode power supplies. They should all be using isolated power converters. If we take the flyback converter as an example, it is already switching the primary side coil creating a hard edge into the transformer. More hard spikes aren't going to significantly change the power conversion there besides confuse the feedback circuitry some. The main concern here then is the passing of odd harmonics of a square wave through the flyback transformer which then aren't properly filtered. This could cause more noise on the output, but since the mains frequency is much lower than the converter switching frequency, it shouldn't cause significant power spikes down the line. It would more than likely cause voltage drooping so if you have an application that would be sensitive to lower frequency electrical noise (audio equipment), I would avoid a MSW inverter.

Last note: An MSW may not raise the power to Vdd. Instead it may raise it to \$ 1/\sqrt{2}~=0.707 Vdd \$ the RMS or some other value to improve efficiency or to better match the expected sine wave. It may also reduce the on-time of the MSW as well which would increase efficiency but reduce total extracted power. My calculations above are somewhat worst-case scenarios.


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