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What Is a Power Inverter?

Power inverter with DC plug.
Large power inverters are used to convert the DC power that is generated by wind turbines into AC power that can be used in a home.
A power inverter takes DC from solar panels and converts it to AC power.
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  • Originally Written By: R. Kayne
  • Revised By: Heather Bailey
  • Edited By: L. S. Wynn
  • Last Modified Date: 11 July 2014
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A power inverter is a device that converts DC power (also known as direct current), to standard AC power (alternating current). Inverters are used to operate electrical equipment from the power produced by a car or boat battery or renewable energy sources, like solar panels or wind turbines. DC power is what batteries store, while AC power is what most electrical appliances need to run so an inverter is necessary to convert the power into a usable form. For example, when a cell phone is plugged into a car cigarette lighter to recharge, it supplies DC power; this must be converted to the required AC power by a power inverter to charge the phone.

How Inverters Work

DC power is steady and continuous, with an electrical charge that flows in only one direction. When the output of DC power is represented on a graph, the result would be a straight line. AC power, on the other hand, flows back and forth in alternating directions so that, when represented on a graph, it appears as a sine wave, with smooth and regular peaks and valleys. A power inverter uses electronic circuits to cause the DC power flow to change directions, making it alternate like AC power. These oscillations are rough and tend to create a square waveform rather than a rounded one, so filters are required to smooth out the wave, allowing it to be used by more electronic devices.

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Most electronic devices require AC power to work correctly because they are designed to be plugged into a standard wall outlet, which supplies AC power. These devices need a specific amount of low, regulated voltage in order to operate. AC power is easier to step up or down, or change from one voltage to another, than DC and easier to regulate. In many cases, when a power inverter is in use, DC power is being converted to AC power, which is then stepped down and turned back into DC power inside the device.

Types of Inverters

Most modern power inverters produce either modified square (or modified sine) waves, or pure sine (or true sine) waves. Modified square wave inverters don't provide the smooth peaks and valleys that AC power from a home's electrical outlet does, but it can deliver power that is consistent and efficient enough to run most devices. This type of inverter is relatively inexpensive, and probably the most popular type.

Pure sine wave inverters are the most expensive, but they also deliver the smoothest and most even wave output. Any device will run on a pure sine wave, but some sensitive equipment, like certain medical equipment and variable speed or rechargeable tools, requires this type of inverter to operate correctly. Radios, for example, work better with pure sine wave inverters because the modified square wave inverter's less-smooth waves disrupt the radio's reception, causing static and other noise.

Inverter Uses

Basic power inverters are often small, rectangular devices that plug directly into the cigarette lighter or DC outlet on the dashboard of a car or other vehicle. This size inverter is usually sufficient to run a laptop, a small television, a portable DVD player, or similar equipment. These devices don’t draw a lot of power and can be used continuously while the vehicle is running; they may even be used for a half-hour to an hour while the engine is off, such as while camping or during a power outage at home.

Other power inverters come with jumper-like cables so they can be connected directly to a battery. This type is required to run more powerful equipment, such as power tools at a remote work site or a larger TV. Inverters can also be hard-wired into a battery to make them easier to use with larger pieces of equipment.

Larger inverters are used to convert solar or wind energy into AC power that can be used in a home. Called a grid-tie inverter, this device links into the utility grid to allow power to be delivered along the same wires that supply energy from a electric utility. It even allows any excess power produced to be fed back into the grid, where it can be sold to the utility company.

Inverter Capacity

Different models of power inverters vary in how many watts of power they can supply. The capacity of an inverter should equal the total number of watts required by each device, plus at least a 50% addition to account for peaks or spikes in the power draw. For example, if a DVD player draws 100 watts and a small TV another 100 watts, a minimum 300-watt inverter is recommended. Getting an inverter with more capacity than what is immediately needed is a good idea for many people, as it means that different or new devices can be added without the need for a new power inverter.

Safety

When using a power inverter continuously inside a vehicle that is not turned on, the engine should be started at least once an hour for 10 to 15 minutes to keep the battery from running down. A vehicle should never be started in a closed garage, as the carbon monoxide in the exhaust is fatal.

Power inverters should only be used with batteries that are in good condition and fully charged. A weak battery will be drained easily if demand is too high. If used in a car, this could leave a driver stranded, so the battery's condition should be checked before using an inverter in a stationary vehicle. If the inverter is being used while the vehicle is running, as in the case of a road trip, there should be no problem with the extra draw as long as the battery is in good condition.

Working with large batteries can be dangerous, and when not done properly, can result in serious injury. Improper use of a power inverter can even lead to electrocution. For safety reasons, someone attempting to hook an inverter directly to a battery should be sure to read and follow any and all safety precautions listed in the inverter's instruction booklet.

It is important for people to always use a power inverter that is rated high enough for the device that needs to be run. If a heavy-duty power saw is plugged into a cigarette lighter, for example, the lightweight inverter might overheat and cause a fire in the dashboard. Adapters that allow more outlets than the unit is designed to accommodate should be avoided, and proper ventilation around the inverter is required to prevent overheating.

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Discuss this Article

anon269774
Post 13

Since when do you need AC to charge a cell phone in a car. The battery in both the cell phone and car have batteries, which are Both DC. Only a regulator would be required.

anon99349
Post 9

Would it be possible to utilize inverter technology to run an electric car and eliminate the problem of battery storage of power?

anon86895
Post 8

We've had a remote cabin for many years, it a great proving ground for AE (Alternative Energy) solutions.

In the beginning, disposable propane bottles fed the cooking stove and the lantern. About 15 years ago, one of our friends bought us a refill adapter that allowed us to fill disposables from a five gallon propane bottle. What a significant savings this seemed to be at the time. Put the empty in the freezer for a bit and then screw it onto the adapter.

Sometimes you got a complete refill in one shot, sometimes you needed to return the bottle to the freezer for an additional cool down. Some folks make a tool that allows them to open the safety valve for refills, but I always thought this was too much trouble. It's a lot quicker to cool em off before filling.

If you're smart, you'll weigh a full bottle and have some idea as to what you need to put back in. If you overfill one, it will vent via the pressure relief valve, and if you have a bunch of overfilled bottles in the trunk, and you have a spark, you could blow yourself up. Building a simple balance scale could help you to fill at the proper weight.

Placing a drop or two of oil into the valve will help you detect an improperly seated (leaking) valve. Sometimes you can plunge the head of a finish nail into a leaking valve and get a proper seat. Only takes a minute to check them. I carry them in our open utility trailer or in the back of the pickup for an added measure of safety. Done properly, it can save you money. You can get the refill adapter at Harbor Freight, and probably lots of other places.

If you're not going to take precautions, spend the extra money and buy the bottles or get an adapter and run your stuff directly from the five gallon or larger bottles. We will probably use the smaller bottles for years; running the propane torch, using the lanterns outside for yard lights. Lighting in the out house. They have their place, and we have dozens of them.

Propane makes noise. Some lanterns seem to make enough racket where they're hard to talk over. On top of this annoyance, they are a safety hazard. The longer you listen to them hiss, the more attractive electric lights get.

Of course, you could try kerosene, we did, but it was difficult to get a good wick, good lamp and good fuel all at the same time. There were times I thought we'd be better off with smudge pots. I know some people get the hang of it, but we never did.

Sooner or later, you rediscover the electric light. I used to grab tail light bulbs out of junked cars, I'd collect them in a little plastic box for replacement bulbs and lighting solutions at one cabin or the other. You often start out with a Deep Cycle battery, insulated terminal from Wall Mart and run 12 volt stuff. Some folks find a little black and white 12 volt TV and enjoy getting a little bit of the evening news.

You can haul your battery back to your vehicle for a charge now and then, but as you would expect this gets old after you do it for a few years, or is it the fact that we get older?

The next step seems to be the modified sine wave inverter. Connect this with short heavy leads to your battery and you will do away with many of the problems found with the poor man's 12 volt system mentioned above. With the inverter, you can power 120 Volt AC compact fluorescent fixtures and have bright lights with a lot less current draw off the batteries.

I personally like the 13 watt twisted bulbs that are found in lots of stores across the country. You can power almost all the small household appliances off a decent inexpensive inverter, TV, Satellite receiver, blender, electric shaver, computer, water pump, mini circuit breaker and much more.

If the modified sine wave inverter was this cheap in 1980, I would have gone this way from the start. The inverter does use a little energy in the standby mode, but running 12 volts any distance creates more losses than a run of 120 volts AC.

After you start living with 120 volts AC off the grid, you start plugging in more things. You discover direct TV, and how easy it is to run your receiver and color TV off a small inverter. In fact, I found our 19 inch color TV, and DSS receiver ran very well off a $40 inverter! Ahh, the cabin is getting very comfortable. Propane for heating water, you can take a hot shower, catch up on the news before bed and enjoy the peace and quiet when you want it.

Pretty soon you're spending more time there and pushing your system to the limits. Vanon Power inverters have the best deals on inexpensive inverters I could find, and I looked a long time. check them out.

You may have arrived at a point in life where it might be worthwhile (or at least fun) to know what the world has to offer in the way of off the grid solutions. There's good news for folks that enjoy working with their hands, because lots of this stuff can be built at home for less money.

If you have wind at your site, consider building your own wind machine, or if you have lots of sun, buy some solar panels and build your own system.

If you're forced to use an engine for your power source, maybe there's a way to harness more of that energy and put it to work heating water for the shower or washing dishes?

anon66323
Post 7

Pure sine wave inverters, or also known as true sine wave inverters, are the mostly preferred kind of inverter because it produces a much cleaner voltage output than modified power inverters.

@anon6969: A varistor’s function is to conduct significantly increased current when voltage is excessive.

Capacitors are widely used in electronic circuits to block the flow of direct current while allowing alternating current to pass, to filter out interference, to smooth the output of power supplies, and for many other purposes. They are used in resonant circuits in radio frequency equipment to select particular frequencies from a signal with many frequencies.

anon54369
Post 5

Ans to gotchanisa 3 : You must be using squrewave unregulated Inverter cum UPS.Please ues any regulated squarewave Inverter or Sinewave regulated Inverter normally sine wave inverters are regulated so you can use sinewave unit. So your 10 mins computer UPS will recognise the incomming power through sine wave inverter and will swicth over to mains mode.

regards,

Umesh S.Belgaonkar

+919820548171

www.uniqueups.com

anon42602
Post 4

what if I can't get my car close enough to the item I want to use? Can I usse a separate battery with clips for the terminals? Thanks, Steve Waters

gotchanisa
Post 3

I have a unique problem: I use a UPS inverter for the whole house. This supplies power for up to 5 hrs during an outage. Of late my computer restarts almost every time this switch happens. It does not restart when the power returns. For a solution, I have used a smaller computer UPS. But I get only 15 mins backup provided by the smaller UPS. It does not recognize the power coming from the main UPS and behaves just like there is no power during this time. I was wondering if a pure sine wave inverter will solve my problem. Is there a cost effective solution to help my computer UPS recognize the power coming from the main UPS. I talked to the UPS manufacturer and he was not able to help :(

I would appreciate an answer. Please bear with me as I have limited understanding into how the whole thing works.

anon6969
Post 2

what are function of varistor and capacitor?

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