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1. What is
a power inverter?
2. How can an inverter be used?
3. What is the difference between Square,
Modified & Pure Sine Wave Inverters?
4. What size inverter do I need? (Starting
Load and Continuous Load)
5. What is the difference between Automotive
and Deep Cycle batteries?
6. How do I charge the battery for
my inverter?
7. What are some safety precautions
to keep in mind?
1) What is a power inverter?
A power inverter is a device that converts DC (Direct
Current) power into AC (Alternating Current) power.
The AC output is usually 120 VAC, 60 Hz (USA domestic
power) or 230 VAC, 50 Hz (International power).
Aircraft applications often require 115 VAC, 400
Hz. Nova Electric offers all three of these common
output voltages, in both single and three-phase
configurations, as well as other special / custom
outputs.
2) How can an inverter be used?
With a large enough battery bank, or a large enough
alternator output from a vehicle, almost anything
within reason can be operated from a power inverter
– this assumes that the inverter has the proper
power output for the given load. Everyday appliances
such as microwaves, power tools, TVs and VCRs, lights,
audio/visual equipment, battery chargers, and computers
are common loads. An inverter sized for loads with
heavy inrush current can be used to power air compressors,
water pumps, heaters, ventilation fans, and air
conditioners. Nova Electric’s Pure Sine Wave
inverters are ideal for running sensitive test equipment
such as communications equipment, oscilloscopes,
scales, high end stereos & video equipment,
communications equipment, etc.
3) What is the difference
between Square Wave, Modified Square Wave &
Pure Sine Wave Inverters?
Square Wave: Nova Electric
neither recommends nor offers any inverters that
produce a square wave. Square Wave units could be
harmful to some electronic equipment, especially
equipment with transformers or motors. The square
wave output has a high harmonic content which can
lead such equipment components to overheat! Square
Wave units were the pioneers of inverter development
and, like the horse and buggy, are no longer relevant
for modern use.
Modified Square Wave: The most
common, general-use inverters available are of the
"Modified
Sine Wave" variety, usually available at more
moderate pricing compared to pure sine wave models.
Modified Square Wave (or “Modified Sine Wave”
and “Quasi Sine Wave”) output inverters
are designed to have somewhat better characteristics
than Square Wave units, while still being relatively
inexpensive. Although designed emulate a Pure Sine
Wave output, Modified Square Wave inverters do not
offer the same perfect electrical output. As such,
a negative by-product of Modified output units is
electrical noise, which can prevent these inverters
from properly powering certain loads. For example,
many TVs and stereos use power supplies incapable
of eliminating common mode noise. As a result, powering
such equipment with a Modified Square Wave may cause
a "grain" or small amount of "snow"
on your video picture, or "hum" on your
sound system. Likewise, most appliances with timing
devices, light dimmers, battery chargers, and variable
speed devices may not work well, or indeed, may
not work at all. For this reason, Nova Electric
offers only Pure Sine Wave Inverters!
Pure Sine Wave: Nova Electric offers
only Pure Sine Wave output Inverters, which are
mandatory for powering any device that requires
sensitive calibration. Pure or True Sine Wave inverters
provide electrical power similar to the utility
power you receive from the outlets in your home
or office, which is highly reliable and does not
produce electrical noise interference associated
with the other types of inverters. With its "perfect"
sine wave output, the power produced by the inverter
fully assures that your sensitive loads will be
correctly powered, with no interference. Some appliances
which are likely to require Pure Sine Wave include
computers, digital clocks, battery chargers, light
dimmers, variable speed motors, and audio/visual
equipment. If your application is an important video
presentation at work, opera on your expensive sound
system, surveillance video, a telecommunications
application, any calibrated measuring equipment,
or any other sensitive load, you must use a Pure
Sine Wave inverter.
4) What size inverter do
I need? (Starting Load and Continuous Load)
The power output rating of the inverter you choose
(in VA or in watts) is directly dependant on the
load you will be powering. It
is absolutely critical that you select an inverter
which is powerful enough to operate your specific
loads.
Step 1: The first
step in your inverter selection is to calculate
the total (Watts or Amps) of all appliances you
plan to power. Virtually all AC powered equipment
will bear a label (usually placed near where the
power wire enters the unit), indicating how many
Amps or Watts of electricity the equipment uses.
Step 2: The second step is to determine
the characteristics of your load. AC loads generally
fall into two categories: Electronic loads, such
as switching power supplies (or SMPS, as found in
computers), and motors, such as the compressor in
a refrigerator. Both of these types of loads require
different levels of the initial surge of power required
to start up, often called a Peak Surge for electronic
loads, or Locked Rotor Current for motor loads.
The Peak Surge or Locked Rotor Current is almost
always considerably higher than the Continuous Load
(which is the power needed to run the load after
initial start up) and must be considered when sizing
the inverter, the battery, and the cables that connect
the two. The following formulas should therefore
be strictly observed:
Electronic Load / Switching Power Supply:
Some SMPS type load are extremely reactive, with
a poor power factor at the input, due to very high
peak current and high harmonics content at the input.
Consequently, selecting a high-frequency topology
inverter with a power output rating equal to or
only slightly greater than the power rating of the
load will result in an overloaded inverter, with
a distorted wave shape at the output. Therefore,
for high-frequency topology inverters (GL and CGL
Series), Nova Electric suggests maintaining a ratio
of 3:1 between the power output rating of the inverter
in VA, and the rating of the load in watts.
For example, if a GL or CGL Series Inverter is to
be used, we would recommend powering a 300 watt
telecom gear load with an inverter which has a minimum
power output rating of 900 VA. For units
which have a transformer isolated topology (such
as our GS or Classic Series), this ratio can be
reduced to 2:1 (e.g., a 1,000W SMPS load can be
powered by a 2 KVA inverter). In effect,
the tradeoff for utilizing a lightweight, compact
high frequency topology inverter is the requisite
higher ratio between the power rating of the inverter
and the power rating of the load.
Motor / Compressor Load: Nova Electric
does not recommend the use of high frequency inverters
(GL or CGL) for motor or compressor loads in general,
though they can be modified for such use in certain
applications where weight savings are critical (consult
factory for details). Whenever possible, we recommend
using the low-frequency transformer isolated GS
or Classic Series models for motor loads.
The formula to use for all inverters which are to
power motor loads is: Inverter’s output AC
voltage multiplied by Locked Rotor Current of motor
load equals minimum rating of inverter in VA.
For example, if you have a pump which runs off of
120 VAC and has a Locked Rotor Current of 10 Amps,
you would need an inverter of at least 1200 VA to
run the pump (120 VAC x 10A = 1200 VA). It is not
recommended to start two motor loads simultaneously
unless a very large capacity inverter is being used.
5) What is the difference
between Automotive and Deep Cycle batteries
Automotive batteries are usually adequate for small
inverters, (< 500 Watts). When used in a car,
we suggest you run the vehicle of your engine occasionally
while operating your inverter. If you use the inverter
while the engine is off, you should start the engine
regularly and let it run to charge the battery.
Deep Cycle (marine) batteries are best for larger
inverters as they are designed for several hundred
charge/discharge cycles. (Automotive batteries wear
out much more quickly after heavy discharge).
6) How do I charge the
battery for my inverter?
Because inverters operate from a DC (Direct Current)
power source, usually a battery bank (one or more
batteries), the battery source will have to be recharged
at some point. (Remember that a battery discharged
more than 50% is probably close to being dead.)
Most cars and trucks recharge their batteries from
an onboard alternator. Depending on the inverter
load and runtime required, most power use applications
will be covered by the charged battery, augmented
by the operating alternator supplying a continuous
charge to the battery. If the load is large (air
conditioner, large draw power tools, large microwave,
food freezer, ice cream machine, etc.), the user
should verify that the installed vehicle alternator
is of large enough capacity to operate the vehicle's
power requirement as well as to fulfill the capacity
of the inverter load. If it’s not, a motor
throttle installation may be required to carry a
small load, a larger alternator may be required,
or a larger alternator, battery isolator and additional
onboard battery bank may be required in order to
meet the power requirement of the large load. Remember:
it takes 12 DC Amps (at 12 VDC) to run 1 AC Amp
(at 120 VAC single-phase) of power because there
are voltage and efficiency factors to take into
consideration.
7) What are some
safety precautions to keep in mind?
Improper use of a power inverter could result in
personal injury. The inverter should not be installed
in the vehicle’s engine compartment. Keep
the inverter free from moisture as liquids conduct
electricity, which may lead to serious damage or
injury! Do not use the inverter near flammable materials
or where fumes or gases may accumulate. The AC Output
(neutral) wire should be vonded to ground, except
in special applications. See owner’s manual
for more details.
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