Inverter FAQ - - Frequently Asked Questions about Power Inverters

Frequently Asked Questions about Power Inverters
What does a power inverter do, and what can I use one
Using an inverter for basic emergency home backup power
What size inverter should I buy?  (and Formula to
convert Amps to Watts)
Watts Used by Common Appliances and Tools (Usage Chart)
Do I need a Modified Sine Wave Inverter, or a Pure Sine
Wave Inverter?
How do I hook up the Inverter? What size cable should I
use, and is it included?
What type of battery should I use (automotive or deep
How long can I run the power inverter on my battery?
How do I connect two or more batteries together?
Using a Microwave Oven with a Power Inverter
Television and Audio Suggestions
Appliance Cautions
Safety Precautions and Installation Tips (Please Read)
If you don't find your answer here,
Read Jon's Power Inverter Blog ... More Info, Questions
& Answers about Inverters

What does a power inverter do, and what can I use one for?
A power inverter changes DC power from a battery into
conventional AC power that you can use to operate all kinds of
devices ... electric lights, kitchen appliances, microwaves,
power tools, TVs, radios, computers, to name just a few. You
just connect the inverter to a battery, and plug your AC
devices into the inverter ... and you've got portable power
... whenever and wherever you need it.

The inverter draws its power from a 12 Volt battery
(preferably deep-cycle), or several batteries wired in
parallel. The battery will need to be recharged as the power
is drawn out of it by the inverter. The battery can be
recharged by running the automobile motor, or a gas generator,
solar panels, or wind. Or you can use a battery charger
plugged into an AC outlet to recharge the battery.

Using an Inverter for Emergency Home Backup Power
A very simple way to use an inverter for emergency power (such
as during a power outage), is to use a car battery (with the
vehicle running), and an extension cord running into the
house, where you can then plug in electrical appliances.
Click here to read an in-depth Article on Emergency Home
Backup Power

What size inverter should I buy?
We carry many different sizes, and several brands of power
inverters. See our Inverters Page for specifications on each
of our models.
Short Answer: The size you choose depends on the watts (or
amps) of what you want to run (find the power consumption by
referring to the specification plate on the appliance or
tool). We recommend you buy a larger model than you think
you'll need (at least 10% to 20% more than your largest load).

Example: You want to power a computer with a 17" monitor,
some lights,
and a radio.
Computer: 300 Watts
2 - 60 Watt lights: 120 Watts
Radio:10 Watts
Total Needed:430 Watts

For this application, you would minimally need a 500 W
inverter, and should give some thought to a larger one, as
there will likely be a time when you wish you'd bought a
bigger model ... in this example, you might decide you'd
like to run a fan while you compute, or let the kids watch
Longer Answer: Determine Continuous Load and Starting (Peak)
Load: You need to determine how much power your tool or
appliance (or combination of them that you would use at the
same time) requires to start up (starting load), and also the
continued running requirements (continuous load).
What is meant by the terms "continuous-2000 watts" and "peak
surge-4000 watts" is that some appliances or tools, such as
ones with a motor, require an initial surge of power to start
up ("starting load" or "peak load"). Once started, the tool or
appliance requires less power to continue to operate
("continuous load")
Helpful formulas:
To Convert AMPS to WATTS:

Multiply: AMPS X 120 (AC voltage) = WATTS
This formula yields a close approximation of the continuous
load of the appliance
To Calculate approximate Startup Load:

Multiply: WATTS X 2 = Starting Load
This formula yields a close approximation of the starting
load of the appliance, though some may require an even
greater starting load. NOTE: Induction motors such as air
conditioners, refrigerators, freezers and pumps may have a
start up surge of 3 to 7 times the continuous rating.
Most often the start up load of the appliance or power tool
determines whether an inverter has the capability to power it.

For example, you have a freezer with a continuous load of 4
amps, and a start up load of 12 amps:
4 amps x 120 volts = 480 watts continuous
12 amps x 120 volts = 1440 watts starting load
You would need an inverter with peak-surge rating greater
than 1440 watts.
FORMULA to convert AC Watts to DC Amps:
AC Watts divided by 12 x 1.1 = DC Amps
(this is the size vehicle alternator you would need to keep
up with a specific load; for example, to keep up with a
continuous draw of 1000 watts, you would need a 91 amp
Click here for a Chart of Estimated Watts Used by Common
Appliances and Tools

Do I need Modified Sine Wave, or Pure Sine Wave?
Advantages of Pure Sine Wave inverters over modified sine wave
a) Output voltage wave form is pure sine wave with very low
harmonic distortion and clean power like utility-supplied
b) Inductive loads like microwave ovens and motors run faster,
quieter and cooler.
c) Reduces audible and electrical noise in fans, fluorescent
lights, audio amplifiers, TV, Game consoles, Fax, and
answering machines.
d) Prevents crashes in computers, weird print out, and
glitches and noise in monitors.
e) Reliably powers the following devices that will normally
not work with modified sine wave inverters:
Laser printers, photocopiers, magneto-optical hard drives
Certain laptop computers (you should check with your
Some fluorescent lights with electronic ballasts
Power tools employing "solid state" power or variable speed
Some battery chargers for cordless tools
Some new furnaces and pellet stoves with microprocessor
Digital clocks with radios
Sewing machines with speed/microprocessor control
X-10 home automation system
Medical equipment such as oxygen concentrators
We carry a full line of Pure Sine Wave Inverters here at, though most of the inverters we carry are
Modified Sine Wave inverters. Modified Sine Wave works well
for most uses, and is the most common type of inverter on the
market, as well as the most economical. Pure Sine Wave
inverters (also called True Sine Wave) are more suited for
sensitive electrical or electronic items such as laptop
computers, stereos, laser printers, certain specialized
applications such as medical equipment, a pellet stove with an
internal computer, digital clocks, bread makers with
multi-stage timers, and variable speed or rechargeable tools
(see "Appliance Cautions" below). If you wish to use those
items with an inverter, then choose a Pure Sine Wave inverter.
If you mostly want to run lights, TV, microwave oven, tools,
etc, a Modified Sine Wave inverter is fine for your needs.
We often are asked if computers will work with Modified Sine
Wave. It's been our experience that most (with the exception
of some laptops) will work (though some monitors will have
interference such as lines or a hum). However, if you have any
doubt about any appliance, tool or device, particularly laptop
computers and medical equipment such as oxygen concentrators,
we recommend that you check with its manufacturer to be sure
it is compatible with a Modified Sine Wave inverter. If it is
not, choose one of our Pure Sine Inverters instead.
The difference between them is the Pure Sine Wave inverter
produces a better and cleaner current. They are also
considerably more expensive. You might find it practical to
get a small Pure Sine Wave inverter for any "special need" you
may have, and also a larger Modified Sine Wave inverter for
the rest of your applications.

How do I hook up the Inverter? What size cable should I use,
and is it included?
The small inverters (400 watts and under) come with a
cigarette lighter adapter, and may be plugged into your car's
lighter socket (although you will not be able to draw more
than 150 to 180 watts from the cigarette lighter socket). The
small units also come with cables that can be clamped directly
to a battery. If you want an inverter that will plug into your
cigarette lighter, you must choose one that is 400 watts or
Larger inverters (500 watts and over) must be hard-wired
directly to a battery. The cable size depends on the distance
between battery and inverter, and will be specified in the
Owner's Manual.
When connecting the inverter to the battery use the thickest
wire available, in the shortest length practical.
See our Cables Page for recommendations for each of the
inverters we sell.
General recommendations — Inverters 1500 watts and under: If
battery and inverter are within 4', use #4 gauge AWG. If
4'-6', use #2. If more than 6', use #0 gauge wire (#0 gauge
wire may require a "0 to 4 Gauge Adapter"). The maximum length
generally recommended is 10', and shorter is better. If you
need more length, it is much better to put it on the AC side
(as with an extension cord from inverter to appliance) than on
the DC side.
Inverters over 1500 watts will require #1/0 or larger cable,
in the shortest possible length.
NOTE: Cable size recommendations may vary among inverter
brands and models; check the Owner's Manual for the model you
purchase before you buy the wire for it.
Cables and battery terminals (ring terminals, also called
eyelet terminals) to hook up your inverter are available here.

What type of battery should I use (automotive or deep cycle)?
Small Inverters: Most automobile and marine batteries will
provide an ample power supply for 30 to 60 minutes even when
the engine is off. Actual time may vary depending on the age
and condition of the battery, and the power demand being
placed on it by the equipment being operated by the inverter.
If you use the inverter while the engine is off, you should
start the engine every hour and let it run for 10 minutes to
recharge the battery.
500 Watt and larger Inverters: We recommend you use deep cycle
(marine or RV) batteries which will give you several hundred
complete charge/discharge cycles. If you use the normal
vehicle starting batteries they will wear out after about a
dozen charge/discharge cycles. If you do not have a deep cycle
battery, we recommend that you run the engine of your vehicle
when operating the power inverter.
When operating the inverter with a deep cycle battery, start
the engine every 30 to 60 minutes and let it run for 10
minutes to recharge the battery.
When the inverter will be operating appliances with high
continuous load ratings for extended periods, it is not
advisable to power the inverter with the same battery used to
power your car or truck. If the car or truck battery is
utilized for an extended period, it is possible that the
battery voltage may be drained to the point where the battery
has insufficient reserve power to start the vehicle. In these
cases, it's a good idea to have an extra deep cycle battery
for the inverter (installed close to the inverter), cabled to
the starting battery. It is recommended to install a battery
isolator between the batteries.

How long can I run the inverter on my battery?
To estimate how long a battery/appliance combination
will operate together, use this handy calculator. (Tip:
If the calculator output equals 0 hours, the total
Amp/Hrs of the battery bank are insufficient to run the
load. Try adding additional Amp/Hrs to the battery bank
field in order to run the desired wattage.)

1.Enter the voltage of your battery or bank of
batteries.Battery Voltage  12 Volt 24 Volt
Battery TypeVoltageAmp Hours
22 NF1250
24 NF1275
27 NF12100
8 D12200

2.Enter the total Amp/Hrs of the battery or bank
of batteries.Amp/Hrs  
3.Enter the combined Watt value of the appliances
you plan to run from your battery.Watts  
19" Color TV100
Circular Saw1500
Computer System300
Microwave Oven1100
Power Drill400

Represents actual power consumption as measured on
sample products. Click below for Chart of Typical
Appliance/Tool Usage
4.Click the Calculate button to see the number of
hours your configuration should run.  hour(s) of
operating time, approximate. Based on fully
charged batteries.

Tip: Deep cycle (marine) batteries generally have the highest
reserve ratings. They are also capable of withstanding
repeated drains of power and recharging.
Tip: Engine start batteries should not be discharged below 90%
charged state, and marine deep cycle batteries should not be
discharged below 50% charged state. Doing so will shorten the
life of the battery based on most battery manufacturers
Note: If you intend to use power tools for commercial use, or
any load of 200W for more than 1 hour regularly (between
battery recharging) we recommend installing an auxiliary
battery to provide power to the inverter. This battery should
be a deep cycle type and sized to meet your run time
expectations with the engine off. The auxiliary battery should
be connected to the alternator through an isolator module to
prevent the inverter from discharging the engine start battery
when the engine is off.

How do I connect two or more batteries?
It may be advisable to operate the inverter from a bank of 12
Volt batteries of the same type in a "parallel" configuration.
Two such batteries will generate twice the amp/hours of a
single battery; three batteries will generate three times the
amp/hours, and so on. This will lengthen the time before your
batteries will need to be recharged, giving you a longer time
that you can run your appliances.
You can also connect 6 Volt batteries together in "series"
configuration to double the voltage to 12 volts. Note that 6
Volt batteries must be connected in pairs.
12 Volt Batteries connected in Parallel to double
the current (amp/hours)
6 Volt Batteries connected in Series to
double the voltage to 12 Volts

Operating a Microwave with a Power Inverter
The power rating used with microwave ovens is the "cooking
power" which refers to the power being "delivered" to the food
being cooked. The actual operating power requirement rating is
higher than the cooking power rating (for example, a microwave
with "advertised" rating of 600 watts usually corresponds to
almost 1100 watts of power consumption). The actual power
consumption is usually stated on the back of the microwave. If
the operating power requirement cannot be found on the back of
the microwave, check the owner's manual or contact the

Television and Audio Suggestions
Although all our inverters are shielded and filtered to
minimize signal interference, some interference with your
television picture may be unavoidable, especially with weak
Here are some suggestions that may improve reception:
1. First make sure that the television antenna produces a
clear signal under normal operating conditions (i.e., at home
plugged into a standard 110AC wall outlet). Also insure that
the antenna cable is properly shielded and of good quality.
2. Change positions of the inverter, antenna cables and
television power cord.
3. Isolate the television, its power cord and antenna cables
from the 12 volt power source by running an extension cord
from the inverter to the TV set. Insure that any excess AC
power cord is a distance away from the TV set.
4. Coil the television power cord and the input cables running
from the 12 volt power source to the inverter.
5. Attach a "Ferrite Data Line Filter" to the television power
cord. More than one filter may be required. These are
available at electronic supply stores including Radio Shack
(Radio Shack Part No. 273-105)
NOTE: Some inexpensive audio systems may discharge a slight
"buzzing" sound when operated with an inverter. This is caused
by deficient filters in the audio system. The only solution to
this problem is using a sound system with a higher quality
power supply.

Appliance Cautions:
DO NOT plug small appliances into the inverter AC receptacles
to directly recharge their nickel-cadmium batteries. Always
use the recharger provided with that appliance.
DO NOT plug in battery chargers for cordless power tools if
the charger carries a warning that dangerous voltages are
present at the battery terminals.
Not all fluorescent lamps operate properly with an inverter.
If the bulb appears to be too bright, or fails to light, do
not use the lamp with an inverter.
Some fans with synchronous motors may slightly increase in
speed (RPM) when powered by an inverter. This is not harmful
to the fan or to the inverter.
Certain rechargers for small nickel-cadmium batteries can be
damaged if plugged into an inverter. In particular, two types
of appliances are susceptible to damage:
Small, battery-operated appliances such as flashlights,
cordless razors and toothbrushes that can be plugged
directly into an AC receptacle to recharge.
Certain battery chargers for battery packs that are used in
some cordless hand-tools. Chargers for these tools have a
warning label stating that dangerous voltages are present at
the battery terminals.
DO NOT use an inverter with the above two types of equipment.
The majority of portable appliances do not have this problem.
Most portable appliances use separate transformers or chargers
that plug into AC receptacles to supply a low-voltage DC or AC
output to the appliance. If the appliance label states that
the charger or adapter produces a low-voltage DC or AC output
(30 volts or less), there should be no problem powering that
charger or adapter.

Safety Warning: 110 Volts of current can be lethal. Improper
use of a power inverter will result in property damage,
personal injury, or loss of life. Please read and follow
carefully the instructions in the Owner's Manual provided with
every inverter for important safety considerations and
General Safety Precautions and Installation Tips:
Place the inverter on a reasonably flat surface, either
horizontally or vertically.
The inverter should not be installed in the engine
compartment, due to possible water/oil/acid contamination,
and excessive heat under the hood, as well as potential
danger from gasoline fumes and the spark that an inverter
can occasionally produce. It's best to run battery cables to
a dry, cool inverter mounting location.
Keep the inverter dry. Do not expose it to rain or moisture.
DO NOT operate the inverter if you, the inverter, the device
being operated, or any other surfaces that may come in
contact with any power source are wet. Water and many other
liquids can conduct electricity which may lead to serious
injury or death.
Avoid placing the inverter on or near heating vents,
radiators or other sources of heat. Do not place the
inverter in direct sunlight. Ideal air temperature is
between 50° and 80° F.
In order to properly disperse heat generated while the
inverter is in operation, keep it well ventilated. While in
use, maintain several inches of clearance around the top and
sides of the inverter.
Do not use the inverter near flammable materials. Do not
place the inverter in areas such as battery compartments
where fumes or gases may accumulate.

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