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pure sine wave inverter

What is a pure sine wave inverter?

A pure sine wave inverter can provide a nice pure and smooth sine wave current for the load. This current is similar to the electric current that the appliance needs.This can prolong the service of  electric appliances.
pure sine wave inverter
What is a pure sine wave inverter? Because your home appliance like lamps, light, fans, compressors need AC power, that's why you will need a inverter to put direct current (DC) from battery bank to alternating current (AC) home appliance.

 A pure sine wave is a continuous wave that describes a smooth repetitive oscillation.

What appliance run by a pure sine wave inverter?

pure sine wave inverter
Pure sine wave inverters are typically the most expensive of the bunch. That’s because they produce AC power that most closely matches an actual sine wave just like the city grid. A pure sine wave is a steady, continuous wave that provides a smooth, periodic oscillation.

Another note is that certain devices will only work with pure sine wave inverters, if you use a modified sine wave inverter, there are risks that will damage the device.

A pure sine save inverter can offer appliance below:

  • Appliances use a motors, such as compressors, water pump or air conditioner
  • Device be powered by a DC adapter, like battery chargers or your phone chargers
  • Applianceuse a rectifier, like refrigerators, computers
  • Delicate piece of medical equipment, such as many CPAP devices for sleep and oxygen concentrate

Pure sine wave inverters cover all appliance, make sure the inverter power is bigger than all home appliances. Click here to understand how to read a inverter data sheet

How does a pure sine wave inverter work?

Mode of operation of an inverter is divided in three stages: oscillator, amplifier, and output transformer stage.
  • Oscillator stage

The inverter generates oscillating pulses through an IC circuit in this stage. Alternate positive and negative voltage peaks generate by these oscillations with a particular frequency. They are very weak and can never be used to power up high current output transformers.So these pulses are sent to the amplifier of the inverter for the required task.

pure sine wave inverter
  • Booster or amplifier stage

The alternate voltage generated by pure sine wave inverter oscillator amplified to high current levels in this stage. Amplified electricity is in AC form, the voltage is still at the battery supply level, which is too low to operate an electrical appliance. To raise the voltage to levels that is suitable for electrical appliances, the amplified voltage is applied to the output transformer secondary winding.

pure sine wave inverter
  • Output transformer stage

In an AC to DC transformer, the power supply is reduced or stepped down to lower specified AC levels through the magnetic induction of the transformer’s two windings. The transformer in a power inverter works in a similar way, but in a reversed manner.

The low level AC power from the amplifier stage of the inverter is applied to the secondary windings of the transformer in the output transformer stage. This process results in an induced stepped up voltage, which is used by power inverter to power AC appliances.

pure sine wave inverter

What is a modified sine wave inverter?

pure sine wave inverter
A modified sine wave is like a block sine wave inverter. A modified sine wave inverter is the most commonly used inverter to work and can drive most equipment.

Appliances that have electronic speed controls (such as mixers) or those with timers may have problems and may be damaged from the modified sine wave.

Also, anything with a motor may not run as efficiently as it would with a pure sine wave. In addition, noise may be generated due to fast transitions in the waveform. This can result in buzzing in speaker systems. As a result of these problems, the modified sine wave has limited use.
pure sine wave inverter

What appliance run by a modified sine wave inverter?

A modified sine wave inverter can work well for ordinary equipment and appliances,

  • Tablets, televisions, and cameras
  • Laptop

A modified sine wave inverter can be seen for cars. Which convert DC current from car battery to AC for other home appliances.

Like we mention, using the modified sine wave inverter will have noise, and some appliance will be damaged or over heated if long time using.

How does a modified sine wave inverter work?

In modified sine wave inverters, the polarity abruptly switches from positive to negative. The simplest inverters produce a square wave, where the polarity is flipped back and forth, while other modified sine wave inverters create a series of steps that more closely approximate an actual sine wave.

A pure sine wave VS a modified sine wave inverter

Pure sine wave


  • Smooth and clear output, can be used in medical equipment
  • Make equipment works better



  • High price, 2 times than modified sine wave inverter


Modified Sine Wave


  • Price cheap



  • Some equipment cannot use


Modified sine waves inverter are simpler for production, no need transformer, only work with fewer PCB board. So that the price is cheaper than pure sine wave inverter compare to same power.


And about efficiency, modified sine waves max about 70% working, cannot 100% woring. And this could build up of excess waste heat, will hurt the equipment if long time working.


A modified sine wave inverter will have Interference in some appliance working. Like a radio, the modified sine wave may results in a buzzing sound during the operation.


Pure sine wave inverter will become more affordable when the cost continues to drop. And if your home appliance is simple and limited to power, a modified sine wave inverter would be a good choice.

However, we still suggest to use a pure sine wave inverter in the solar or wind power system. Because the inverter is the key of a system, the inverter can make the system working more efficiency and safe.

If you are not sure which is more suitable for you about pure sine wave or modified sine wave inverter, or you have further questions, you can contact InkPV for help.

Case- how a pure sine wave inverter supply power to a CT machine

In last month, we send out the UPS system to a medical bus to supply power to the CT machine and 4pcs air conditioner. There are a pure sine wave inverter and a lithium battery included in the UPS system.
UPS system work for a medical bus
INKPV 80kw lithium battery UPS system for a medical CT car.
This is a medical bus equipment with a 80kw pure sine wave inverter and a 380V 150Ah lithium battery.

Because the medical bus space is limited, the pure sine wave inverter and lithium battery suitcase is spacial design by us to fit the space.
There are a CT machine in the car, and the pure sine save inverter supply power to the CT machine.

Because the CT machine needs a stable power source, that’s why will need a UPS system, because not all places enjoy stable city grid.

Where the remote place no stable city grid, the pure sine wave inverter will supply power to the CT machine using the lithium battery power.
pure sine wave inverter

If you are interested about this case, click here to see more how the UPS system work for a medical bus, or contact us for more information.

Why do the CT machine need a pure sine wave inverter?

Medical equipment is a kind of equipment that has very high requirements for power quality. 

In addition to medical equipment related to technology and performance of the machine itself, every medical machine is equip with a voltage stabilizer.

The normal use of medical equipment is related to the life of the patient, a little bit mistake will cause bad result.

That's why the medical machine needs a special voltage regulator for medical equipment is generally used to maintain the stability of the output voltage.

Why does InkPV pure sine wave inverter meet the medical need?

  • If there are grid to supply power, our pure sine wave inverter will use grid to supply power first. And if the grid is very stable, the inverter will use bypass and the grid supply power to the CT machine.
pure sine wave inverter
  • And if the grid voltage suddenly drop or high, the inverter will switch to use the lithium battery power to supply CT machine.
pure sine wave inverter

Why the output is stable via the pure sine wave inverter?

pure sine wave inverter
This is the working diagram for the pure sine wave inverter.

The power from the battery is transfer to AC by the filter, IGBT and the transformer, output filter.

That’s why the pure sine wave inverter can output the stable power to the medical machine.
pure sine wave inverter
When operating from battery power, a line interactive UPS generates the waveform of its AC output. An online UPS does this continuously. All online and many UPS systems have pure sine wave output.

Pure sine wave inverter output provides maximum stability and superior compatibility with sensitive equipment. Pure sine wave power is required by some equipment power supplies and prevents others from overheating, malfunctioning or failing prematurely.

Related questions

What size of inverter do I need?

Solar inverter come in a range of size. Usually we size the inverter by output power, which are rated in watts. 

A inverter power should bigger than your home appliances power. and if you have pump or air conditioner, should consider 4-6times than rate power because there are motor inside.

For InkPV off-grid inverter. We have

  • 1-30KW for single phase
  • 5-250KW for three phase
The off grid inverter can work with both solar and wind power system. Because the working way is to put DC to AC current.

What DC voltage do I need for a inverter?

Inverter voltage is related with the battery number.Inverter voltage is related with the battery number. Just like a 5kw inverter, the DC voltage can be choose like 48V and 96V.

And for the 48V inverter, the max discharge current is
and for the 96V, the max discharge current is
52A<104A, the lifetime of the device is therefore longer.

What is better pure sine wave or modified sine wave?

If you only use the appliance like in a camp,not long time using, and home appliance are small and limited. We suggest to use a modified sine wave inverter. Because you are just use in a short time. And no need to worried about the damage for the fans, and lights.

And for a solar system, better to use a pure sine wave inverter. Because the inverter will supply to home appliance in a long time. And home appliance is complicated, pure sine wave is good for home appliance life span. And every home device can use pure sine wave. Modified sine wave is rough and have risk hurting home appliance life span.

Do I need a pure sine wave inverter for my laptop?

However, most electronic devices run well on a modified sine wave. For example, laptop computers, cellphone chargers, and all other equipment that uses a rectifier or AC/DC adapter to take an AC input and output DC to the device will typically work fine without a pure sine wave inverter.

For most electronic devices, like laptop computers, cellphone chargers. There are a rectifier or AC/DC adapter, which no need pure sine wave. It means the devices can run by a modified sine wave inverter.

A charger uses a rectifier to produce DC, and perhaps a filter capacitor to smooth it. The rectifier only conducts on the peaks of the input waveform, so it doesn’t care about the shape of the waveform.

Will modified sine wave inverter damages my home appliance?

For appliances like refrigerators and air conditioner, its better to use a pure sine wave inverter to supply power.

Because if the appliance work in modified sine wave, the efficiency is not good. They would be damaged if excess waste heat.
Jim Lai
Jim is the creator of InkPV. An good solar installer,  he is passionate about all aspects of solar projects for the home and commercial.

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