BUYER’S GUIDE: Power Inverters

A power inverter converts 12 volt DC power to standard household 110-120 volt AC power, which allows you to run AC electrical equipment off your car or marine battery for mobile applications, emergencies or simple convenience.

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.

Power Inverter

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.

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.

The estimated watts for the appliances below are estimates; please check your manual or the appliance itself for the actual wattage required. Doing this will ensure you select the correct inverter the first time.

Appliance Est. Watts
Cell Phone 24
CD Player 40
VCR 50
Satellite Dish 75
Printer 75
Laptop 60-90
iPod 120
PS2/XBox 125
25″ TV 175
CPAP 200
Jig Saw 350
Computer & Monitor 400
Blender 400
Refrigerator 500
1/2″ Drill 700
Vacuum 750
Coffee Maker 800
Iron 1000
Sub Pump 1000
Space Heater 1000
40″ Fan 1100
Toaster 1200
Circular Saw 1250
Microwave 1250

Typical Uses

Most power inverters under 300 watts can be connected to a vehicle’s 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.

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.

True Sine Wave or Modified Sine Wave?

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

  1. Modified Sine Wave
  2. 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. The Vector power inverter line is based on modified sine wave technology.

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° F. Batteries will discharge much quicker at lower temperatures.

Safety Tips

Sine Wave Inverter SA-1X000

  • 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 vehicle’s 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.

Jeff Flowers

About Author

Jeff Flowers has been a self-described beer geek for over a decade now. When he's not chasing his daughter around, you can usually find him drinking a fresh brew and wasting too much of his time on both Google+ & Twitter.


  1. says

    Thanks for your Web Article about 12 volt power inverters ! I am rigging my 21 Watt 120 VAC Ibanez T20 guitar amplifier to a small 175 Watt Vector Maxx (350 Watt peak) inverter with cigarrette lighter connector into my Super Auto Start POWER PACK portable Auto Jump Starter Unit. To Play my Harp amplified at an out door, in a vineyard Wedding Ceremony. It all fits neatly on a suitcase dolly, I’d better test it out now. hhh

  2. Gary says

    This is very informative post. It covers several important topics of the power inverters. Thank you very much for sharing.


    What size of inverter can power a chest deep freezer, also is it possible to synchronize inverter of different sizes

  4. Rey Dalumpines says

    Is it possible to use 12v AC power FOR inverters to supply 240V appliances to maximize POWER consumption?

    thank you

  5. Charlemagne Parato says

    what is the POWER DRAW from a battery while it is running? it that variable based on power going out of it?

  6. william wright says

    can I run my 300 watt inverter off my batteries and run my battery charger that comes from my converter in the motorhome at the same time ? thx.

  7. Jose Baez says

    I have a wet vac that is 3.0 peek I tried a 750 inverter n it kept shutting off will a 1000 be good or do I need like a 1500. I own my own mobile details service sometime I will use a 100 psi air compressor. Please help me get this right. Thank you for your time.

  8. Bud says

    Hi, I bought a Xantrex 700 W inverter. Is it safe to plug into a car’s cigarette lighter socket for just running a printer while on the road? I know for bigger consumption the lighter will not do.

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