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Jan 30

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Power Inverters: 101

posted by Patrick Fallon

Power inverters are wonderful devices with a whole host of benefits and applications.  They are designed to convert DC, or direct current power to AC, or alternating current power.

Power Inverters—Your Emergency Backup:

DC electricity comes in a range of readily available sources such as batteries and fuel cells.  Power inverters enable the DC power to be converted to AC power so AC-compatible equipment and appliances can operate seamlessly and safely.

Imagine yourself in a power outage for hours….days….weeks or more.  It happens more frequently than we would like it to admit—Hurricane Katrina, Hurricane Sandy, Midwest tornadoes, severe rain or snow storms—it’s unavoidable.  In the event of a power shutdown, an inverter is extremely useful as a power backup.  You would be able to continue to use lights, computers, kitchen appliances, cell phones, etc.   It’s important to remember, though, that not all appliances should use the same type of power inverter.

Not All Power Inverters Are Created Equally:

** True Sine-Wave Inverters:

These power inverters are designed to replicate power-utility quality or main-grid quality power which businesses and households receive from main power grids or power utilities.  True Sine Wave Inverters are constructed to accommodate high energy-consuming electronic gadgets and equipment.  Since this type of inverter is rated higher in power and efficiency, it is more expensive.

** Modified Sine Wave Inverters:

Modified Sine Wave Inverters are less expensive since they are designed to run fewer appliances and fixtures.  Lights, small power tools and some kitchen appliances work well with modified sine wave inverters.


There are a variety of sizes of power inverters from as low as 100W to 5000W and much higher.  These ratings simply designate the volume with which the inverter can simultaneously and continuously power a high-wattage device or a combination of multiple electronics.


Ratings of power inverters are determined according the power needs of any given device.   The three ratings include:

1:  Surge Rating:

Surge rating is important to know and you’ll determine the appropriate surge rating according to the appliance or device you wish to power.  Refrigerators and TVs, for example, demand a high surge to begin operation.  They will need far less power, however, to continue running but one must choose an inverter that has the ability to retain the surge rating for a good 10 seconds.

2:  Continuous Rating:

Continuous means nonstop; and a power inverter should be selected that has the needed power to run continuously without overheating or shutting down.

3:  30-Minute Rating:

Some power inverters will have a continuous rating that will be well below what is needed to power certain appliances or devices, but if that power inverter has a 30-minute rating, it may be adequate to run a high energy-consuming appliance as long as it used sporadically.

Calculating Inverter Requirements:

Get out your calculator!  There are a few steps involved, but nothing overly complicated:

1:  Your appliances will have a name plate which will indicate the maximum rating in amps and volts.  Jot down that info for every appliance you use.

2:  Amps X Volts = Watts.  For larger appliances such as freezers, multiply the amps by two.

3:  Multiply the watts, used by each appliance, by the number of hours the appliance is used each day.

4:  Multiply hours appliance is used per day by days used in a week.

5:  To find average watt-hours per day per appliance, simply divide the answer in #4 by 7.

6:  Add # of watt hours per day for all appliances to get total average daily load—you will get wattage needed to power entire home.

7:  Decide which appliances you will run simultaneously and use only those as your peak load.  Inverters should be sized 25% more than expected peak load.

This has been a brief overview, but contact a power inverter specialist for more details!

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