Power Inverters Buyer's Guide

Need to power your favorite electrical devices when AC power is not available? A power inverter changes DC power from a battery into conventional AC power that you can use to operate devices like electric lights, kitchen appliances, microwaves, power tools, TVs, radios, computers and more. Inverters can deliver mobile AC power in vehicles and boats, when camping, emergency backup power and more. Our Power Inverters Buyers Guide will help you select the inverter that's right for your power requirements.

Typical Power Inverter Uses

Most power inverters under 300 watts can be connected to a vehicles battery through the DC (cigarette lighter) plug on the dashboard. They might also come with jumper-like cables for connecting directly to a battery. Larger units are often hardwired into vehicles, RVs or boats. Inverters normally have one or more standard outlets to power laptops, small-screen TVs, video game players or portable DVD players and other devices. A DC to AC power inverter is great for camping at parks that do not provide electricity. The toaster, blender, and boom box can all still be used. On your boat, you can plug in devices like a digital movie camera to take videos after the camera's battery runs low, or brew up a pot on-board with your coffeemaker.

Inverters that have built-in GFCI protection are advised for powering portable electrical devices outside of the house. Ground fault protection is a feature that instantly turns off the inverter if it gets damp or wet. The inverter then resets, senses the conditions and turns itself back on if the problems have been resolved. The GFCI feature protects the user from electrical shocks and the potential risk of a fire.

Some power inverters have a built-in transfer switch so you can switch from inverter power to utility power when available. This is useful in RVs and boats where shore power is available and when you sometimes want to run from generator power. The transfer switch allows external power to be transferred to appliances automatically. Typically this feature is found on more expensive high-end inverters.

A power inverter is also an essential part of a solar power system. It converts the DC power generated by solar panels and stored in 12 volt batteries to 120 volt AC power suitable for household or industrial use. These systems can be costly, as they often involve additional electrical work and equipment to incorporate the system into a household's current electrical system.

During a utility outage a power inverter can be used for temporary emergency electricity. Just connect the inverter to your cars battery and run an extension cord from your car into the house, or if you have a charged spare battery you can connect the power inverter directly. Plug in a radio to tune into important alerts, run essential medical equipment, lights, or whatever else you need that falls within the inverter's power limits.

Power Inverters

Power Inverter or Generator?

Whether to use an inverter or a generator depends on the type of load and how often you will need emergency AC power. Generally, an inverter is more economical power alternative to run items under 1000 watts, suitable for small appliances, TVs, VCRs, DVD players and other low load devices. If you plan to operate a refrigerator, freezer, washer, dryer or well system, then a generator is a better choice. If your planned power consumption exceeds 2000 watts, you should choose a generator, as the draw in the battery will rapidly deplete its power.

Choosing the Right Inverter Size

Power inverters come in many sizes, measured in watts. The amount of wattage you will require depends on the total draw of the devices you'd like to use.

Many appliances and power tools have their wattage rating indicated on the product itself. Wattage rating can also be calculated by using this formula:

Volts (120) x Amps = Watts

To determine if several appliances can be operated at the same time, simply add up their wattage ratings to see if the total falls within the specifications of the power inverter. For example, if you have a two-outlet inverter and will be plugging in 2 devices at once, add up the total wattage of both devices, then add at least 50% more to account for peaks or spikes in the power draw. For example if your DVD player draws 100 watts and your laptop another 100 watts, a minimum 300-watt inverter is recommended.

Make sure the power of the inverter is listed as continuous. Some inverters are listed at a certain wattage, but can only draw that wattage for a short period of time (i.e., 5 minutes) and then will shut off, reset themselves and resume functioning. These outages can be frustrating to you and harmful to the device you are powering.

If the item is motor driven, it requires additional start-up (surge) wattage (typically 2-3 times the continuous wattage required) to start the device. For example, a miter saw that runs at 700 watts might require 1400 watts to start up. If your inverter only supplies 1000 watts, you will not be able to start it up. In this case, you would want to select an inverter rated at least 1400 surge watts to handle start-up needs.

True Sine Wave or Modified Sine Wave?

Power inverters produce one of two different types of wave output:

  • Modified Sine Wave
  • True Sine Wave

Modified sine wave inverters deliver power that is consistent and efficient enough to run most devices adequately. These types of inverters are the most popular and affordable. They are also small and highly efficient.

True sine wave inverters are the most expensive, but they also deliver the most consistent, highest quality wave output. Some sensitive equipment requires a true sine wave, like laptop computers, tool battery chargers, professional audio/video equipment, certain medical devices and variable speed tools. If you aren't sure if the device you want to use requires a true sine wave or not, call the manufacturer to ask. Any AC device will run on a true sine wave inverter, whether it requires it or not.

Battery Basics

  • Batteries should be in good condition. Old or weak batteries should be replaced before connecting them to an inverter.
  • Automotive batteries are not suited to repeated long discharge and recharge cycles. They will have to be replaced more often than a deep cycle battery.
  • Deep cycle batteries are a better choice as a power source for an inverter. They are designed to be repeatedly drained and recharged. It is also a good idea to have more than one battery supplying power to an inverter.
  • The amp hour rating of a battery is the most important measure when choosing a battery for power inverter use. This indicates how many amps a battery can deliver for a specified period (usually 20 hours), showing how long it will run before needing to be connected to a battery charger.
  • To prolong battery life, you should not use more than 50% of the battery's rated capacity before recharging.
  • Reserve capacity indicates how many minutes a battery can deliver a certain amount of current (25 amps for most batteries) at 60-75 degrees F. Batteries will discharge much quicker at lower temperatures.

Safety Tips

  • Always use a power inverter that is rated high enough for the device(s) you are running and avoid adapters that would allow more outlets than the unit is designed to accommodate.
  • When using your power inverter continuously inside a vehicle that is not running, the engine should be started at least once an hour for 10-15 minutes to keep the battery from discharging. Do not start a vehicle in a closed garage, as the carbon monoxide in the exhaust is fatal.
  • Power inverters work best with a battery that is in good condition and fully charged. A weak battery will be drained easily if demands are too high. This could leave you stranded so be sure to check the battery's condition before using a power inverter in a stationary vehicle.
  • If the power 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, assuming the battery and alternator are in good condition.
  • Make sure your vehicles wiring harness can handle the current before plugging in an inverter to your cigarette lighter. You may need to hardwire the inverter directly to the battery to safely use it.
  • Make sure the inverter is properly ventilated. Even a small inverter generates heat. Check to see if there is an internal fan with any inverter over 100 Watts. Place the inverter in a well-ventilated area when in use.
  • Check the owner's manual for the proper wire size for battery cables when connecting the inverter to the battery. Most manufacturers recommend 4 to 10 feet of cable length, depending on the inverter. Avoid aluminum wire because it has higher resistance to current flow than copper wire.
  • Working with car batteries can be dangerous and can result in serious injury, and improper use of a power inverter can lead to electrocution or battery failure, so for your own safety be sure to read and follow any and all safety precautions that are listed in your power inverter owner's manual.

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