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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?

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4 Answers

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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 manufacturer, 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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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. –  bt2 Apr 17 '11 at 15:37
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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? –  davidcary Apr 22 '11 at 1:52
    
Do the "power-factor laws" express conformance in absolute or relative terms? For example, if one had a device which drew 1uA with current leading voltage by 89 degrees, would such a device be non-compliant (power-factor near zero) or compliant (out-of-phase component less than 1uA)? Burning 250uA in a parallel resistor would improve the power factor, but would seem like a silly waste of energy. –  supercat Mar 21 '13 at 16:14
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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.

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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

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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.

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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. –  supercat Mar 21 '13 at 16:16
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protected by W5VO Apr 2 '13 at 4:09

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