When the power goes out and we’re left in the dark, you could rely on candles and fire for light, but what about your food in the refrigerator? Sure, you may have a small power generator, but without a power inverter, that power isn’t going to do much good.
A power inverter is a device that is capable of turning DC (direct current) electricity into AC (alternating current) electricity. The battery in your car and handheld electronics use DC power, and the most common use for the inverter is to hook it up to your car battery and it will act as a source of electricity for appliance in the house that use AC currents.
Think back to science class when your teacher covered the topic of electricity. They probably went over the basic idea of how electricity work, summing it up as a flow of electrons. The electrons flow like ants that march in a line. The electrons carry packets of electrical energy just like an ant would carry food.
For a better example, let’s look at your basic flashlight. There is an unbroken electrical loop that links the battery to the lamp and switch. This electrical energy is then transported to the lamp from the battery until there isn’t any more energy in the battery. The switch is responsible for starting and stopping that flow. This is how Direct Current (DC) works.
The appliances in your home uses electricity differently than your run of the mill flashlight. The electricity that comes from the outlet is called Alternating Current (AC). This is when the electricity switches the direction at which it moves anywhere from 50 to 60 times per second, or 50 to 60 Hz.
Now we get where this may be confusing because if the electricity is always changing its direction, how is the appliance in question going to work? Well, the reasoning is actually pretty simple. Say there is a lamp plugged into the wall.
The cable that connects the lamp to the outlet, and the outlet itself, is loaded with electrons. When you turn the switch to the on position, every one of the electrons in the cable will begin to vibrate back and forth and into the filament in the lamp.
All that rapid vibration is going to convert the electrical energy into head, which makes the light bulb in the lam glow. With AC, the electrons don’t have to go in a circle to move the energy, they can just stay in one place and vibrate like crazy.
We may not think about what kind of electricity powers our home and gadgets, but during the 19th century, people didn’t just fight over land, crops, and religion – they also fought about how to establish which type of electricity is used to power their buildings.
Thomas Edison, the American inventor, insisted that a direct current (DC) was far superior at supplying electrical energy than an alternating current (AC) – which was the system Nikola Tesla praised.
Thomas Edison tried his best to convince people that AC power was extremely dangerous. He even went so far as to electrocuting an elephant to demonstrate just how dangerous AC power is. Even despite Edison’s efforts, Tesla’s argument won out and we have been using AC power ever since.
During this time, the conversion of DC-to-AC was achieved by using rotary converters or M-G sets (also known as motor-generator sets). During the early 1900s people used vacuum tubes (thyratron was the most common tube used) and tubes filled with gas to act as a switch in an inverter circuit.
The earlier AC-to-DC converters would use induction or a synchronous AC motor that was directly connected to a generator. The communicator on the generator would then reverse the connection at the right moments to create DC.
Later, the synchronous converter would have a motor and generator windings that were combined into one armature. This armature would have slip rings on one end and there would be a commutator on the other end and there would be only one field frame. This results in AC-in and DC-out.
If there is an excess of current flowing through the power source, this will result in a short circuit, which could cause the source of the power to be severely damaged. In most instances, there will be a fuse in the supply circuit, so if there is too much power going through, the fuse will blow out, thus causing the circuit to open up and stop the electrical current from flowing.
An inverter that converts DC to AC is just an over-simplification of the process. The output created by an inverter is built up pulsing DC voltages. The process of converting a DC voltage to a sine wave (a curve that represents periodic oscillations of constant amplitude that is given by a sine function) isn’t a clear cut processes.
The basic approach is to pulse the DC voltage so it closely resembles the sine wave. Then this waveform is going to be filters so that it is closer to an actual sine wave. The level and costliness of these processes are going to determine the overall quality of the final sine wave that has been made.
When you’re looking at an inverter, the quality of the input they create is classified into one of output waveforms:
The Square Wave Inverter was the earliest type of inverter that was used in renewable energy applications that creates a coarse square wave AC output. This is fairly easy to do and it’s going to be the most affordable type of power inverter.
When a low-frequency inverter is turned on, the transistors inside will switch on and off about 120 times each second during the AC cycle (this is also referred as switching at 120 Hz).
You can usually tell the low-frequency inverters because they are pretty large and they’re going to be heavier. The reason why they are going to be heavier than other inverters is because they use a large, low-frequency transformer. With that said, these inverters are rugged and reliable. The transformer protects the transistors from damage while it also provides DC-to-AC isolation.
With a high-frequency inverter is turned on, the transistors inside will go on and off about 20,000+ times each second during each AC cycle (this is also referred to as switching at 20KHz). These inverters are going to take a DC source and step it up to a higher AC wave by using a high frequency transformer.
Then this is rectified to a secondary DC voltage that is somewhere between 200 and 400 VDC and that is stored in a pair of capacitors. Then there is an additional pair of output transistors that switch at the low frequency of 120Hz. Then this will create a modified square wave AC output from the high-voltage DC power source.
Creating a sine wave from a DC power source is going to be much harder than creating a square wave or modified square wave form. There are more parts involved, the design is more complex, and the control system is much more sophisticated.
A sine wave inverter is going to be highly efficient, but they weren’t always that way. The older sine wave inverters created low-power loads and they lacked in efficiency.
Through technological advances, the transistors and new high-speed digital control systems can now allow new models of sine wave inverters to give you the high quality power and high conversion efficiencies that you’re looking for – even if you don’t have a high power level.
There are several different types of Sine Wave Inverters:
Low Frequency Ferro-Resonant
As the demand for a better quality sine-wave output grew, engineers looked at the low-frequency square wave inverter and added a filtering system to the output system that would round off the squared edges.
There were some manufacturers that offered output filters that were ferro-resonant transformer-based. These filters improved the compatibility with electronic loads that were fairly sensitive, but still had a big impact on how efficient the inverter was.
Low Frequency Multistep
Engineers created another solution that would make the AC output a little closer to a true sine wave. This solution combines several low-frequency inverters that operate at different frequencies to work together in a series. This would allow several AC output voltage levels to be created, while creating a stepped sine-wave approximation of a true sine wave.
This method takes the benefits of both low-frequency and high-frequency inverters. The switching transistors in the high-frequency inverters would convert the DC power source to a low-voltage AC waveform. Then the transistors would then be switched at a high frequency several hundred times during each AC cycle (20KHz).
The inductor would smooth out the square high-frequency waves and turn them into a smooth, low-frequency wave form – ultimately creating a low-voltage sine wave. Then, the low-frequency transformer would increase the AC voltage to 120 or 240 VAC.
A high frequency sine wave inverter is more complex than the previous examples, but the unit is going to be much smaller and lighter than their low-frequency counterparts.
These units use a two-step power conversion system where the control system dedicates the “front” of the converter (goes from DC-to-AC-to-DC and uses transistors, a transformer, and rectifier) to pull most of the power from the maximum power point tracking (also known as PV array).
The second converter is made of transistors and an output filter that is made of capacitors and inductors, to optimize the power that is going back into the power grid.
High Frequency Transformerless
These power inverters offer the highest efficiency – up to 98%! This is the result of removing the transformer from the inverter. However, this causes another issue, the DC output isn’t going to be grounded, so the PV array is going to be floating.
This means the bridge of the inverter’s transistor will be likely to flip the PV array about 60 times each second. This wasn’t something that was allowed under the National Electrical Code guidelines until recently. These transformerless inverters aren’t typically used for off-grid systems because a battery isn’t capable of being grounded.
The typical power inverter unit is going to need a stable DC power source that is going to be able to supply enough electrical current for your intended purposes. The input voltage is going to depend on the design and the intended purpose of the inverter. For example:
A power inverter’s AC output frequency is going to be the same as your standard power line frequency, which is usually either 50 or 60 Hz. Should the output of the inverter be further conditioned or stepped up, then the frequency you will receive may be higher for proper transformer efficiency.
A power inverter’s AC output voltage is usually regulated to be the same voltage as the grid line. This is usually 120 VAC or 240 VAC upon distribution. Even if there are changes in the load the inverter is processing.
This is going to let the inverter to provide power to several devices that are designed for your typical power line. There are some inverters that give you the ability to choose between a selectable or a continuously variable output voltage.
A power inverter usually has an overall power rating that is expressed in watts or kilowatts. This is used to describe the power that is available while the inverter is processing power, and (albeit indirectly) the power that the DC power source will need to supply.
Smaller devices on the consumer and commercial level have been designed to copy line power that ranges from as little as 150 watts and all the way up to 3000 watts.
Keep in mind that not all uses for an inverter is going to require that you be concerned with the delivery of the power. Some instances, the frequency or the properties of the waveform will be used by the inverter itself, or the follow-on circuit.
Now that we’ve discussed a little more about how power inverters work, you may be wondering what they can be used for. These devices actually have a lot of uses!
A car power inverter can be used by anyone who spends a lot of time on the road. These devices are great for long road trips, camping, business travel, long-haul truckers, etc.
Many devices like televisions, video systems, game systems, cooking equipment, power tools, cellphones, laptops, tablets, and other handheld items can be used with an inverter. You’ll want to plug the inverter into the cigarette lighter with the 12v attachment.
UPS use batteries and an inverter to create AC power when the main power isn’t available. When you do get power back, like after a winter storm, a rectifier will supply DC power to the batteries and recharges them.
The circuits in an inverter is designed to create variable output voltage that is usually used inside motor speed controllers. The inverter section can use DC power that has been derived from the AC wall outlet, but it can also use other sources as well. These units use control and feedback circuitry to adjust the final output of the inverter.
This is going to determine the speed the motor operates while carrying a load. There are many instances where an electric motor speed control is needed, such as with industrial motor equipment, electric vehicles, rail transportation, and power tools.
An inverter could be used to control how fast or slow the compressor motor works inside a refrigeration or air conditioning system. These inverters will regulate how the system performs.
These systems are usually called inverter compressors and the traditional method of controlling the refrigeration will use a single speed compressor. This single speed compressor will switch on and off intermittently, which controls the motor’s speed, compressor, and the cooling output.
An inverter that is connected to a power grid is designed to feed into the distribution system. They work in unison with the line and have very little harmonic content. These inverters need a way of detecting the use of utility power as a safety measure, so that it doesn’t continue to feed power to the grid during a blackout.
A solar inverter is part of a photovoltaic system that balances the system. They can be used for off-grid systems as well as a system that is connected to the grid. These inverters have special functions that have been adapted so they can be used with photovoltaic arrays, like PV arrays and anti-islanding protection.
It’s important to note that a solar micro-inverter isn’t the same as a conventional inverter because there is an individual micro-inverter connected to each solar panel. This set up is designed to improve the systems efficiency and combine the output from a few of the micro-inverters with an electrical grid.
Power inverters can convert low frequency AC power to a higher frequency for the purpose of induction heating. The AC power first needs to be rectified to DC power. Then the inverter will change the DC power into a higher AC power.
Because there is a reduction in the amount of DC power sources, the structure is going to be more reliable and the output voltage is going to have a higher resolution, thanks to the number of steps that has to take place for a sine wave to be made.
A power inverter is a great device if you’re someone who likes to go camping, but you don’t want to be without power for your devices. If you use a camper during your camping trips, you could convert the power from your car’s battery and turn it into usable energy for your television, entertainment devices like DVD or Blu Ray players, gaming consoles, and more.
These devices aren’t just good for when you’re on the road, they can be very useful when you experience a power outage and you need electricity. These devices convert the DC power from one battery and turns it into useable AC power that is needed for most of your appliances in the home.
All you have to do is hook your inverter to your car battery (while the car is running, of course) and connect it to an extension cord. You’ll be able to plug in your refrigerator, portable heater, microwave or even an electric stove.
If you’re thinking that you may need (or want) an inverter so you can be prepared for power outages, camping trips, or anything else, then we have a buying guide to find the best power inverter. In our guide, we go over our top 5 choices that are worthy of your considerations, but we also provide you with what things you’ll want to pay attention to when making your choice.
Our ultimate goal is to provide you the information necessary so you can make a well-informed purchase!