The inverter is one of the most important and most complex components in an independent energy system. To choose an inverter,
you don't have to understand its inner workings, but you should know
some basic functions, capabilities, and limitations. This article gives
you some of the information you'll need to choose the right inverter and
use it wisely.
Why You Need an Inverter
Independent electric energy systems are untethered from
the electrical utility grid. They vary in size from tiny yard lights to
remote homes, villages, parks, and medical and military facilities. They
also include mobile, portable, and emergency backup systems. Their common bond is the storage battery, which absorbs and releases energy in the form of direct current (DC) electricity.
In contrast, the utility grid supplies you with alternating
current (AC) electricity. AC is the standard form of electricity for
anything that "plugs in" to utility power. DC flows in a single
direction. AC alternates its direction many times per second. AC is used
for grid service because it is more practical for long distance
transmission.
An inverter converts DC to AC, and also changes the voltage. In other
words, it is a power adapter. It allows a battery-based system to run
conventional appliances
through conventional home wiring. There are ways to use DC directly,
but for a modern lifestyle, you will need an inverter for the vast
majority, if not all of your loads (loads are devices that use energy).
Incidentally, there is another type of inverter called
grid-interactive. It is used to feed solar (or other renewable) energy
into a grid-connected home
and to feed excess energy back into the utility grid. If such a system
does not use batteries for backup storage, it is not independent from
the grid, and is not within the scope of this article.
Not a Simple Device
Outwardly, an inverter looks like a box with one or two
switches on it, but inside there is a small universe of dynamic
activity. A modern home inverter must cope with a wide range of loads,
from a single night light to the big surge required to start a well pump
or a power tool. The battery voltage of a solar or wind system can vary
as much as 35 percent (with varying state of charge and activity).
Through all of this, the inverter must regulate the quality
of its output within narrow constraints, with a minimum of power loss.
This is no simple task. Additionally, some inverters provide battery
backup charging, and can even feed excess power into the grid.
Define Your Needs
To choose an inverter, you should first define your needs.
Then you need to learn about the inverters that are available. Inverter
manufacturers print everything you need to know on their specification
sheets (commonly called "spec sheets"). Here is a list of the factors
that you should consider.
Application Environment
Where is the inverter to be used? Inverters are available for use in
buildings (including homes), for recreational vehicles, boats, and
portable applications. Will it be connected to the utility grid in some
way? Electrical conventions and safety standards differ for various
applications, so don't improvise.
Electrical Standards
The DC input voltage must conform to that of the electrical
system and battery bank. 12 volts is no longer the dominant standard for
home energy systems, except for very small, simple systems. 24 and 48
volts are the common standards now. A higher voltage system carries less
current, which makes system wiring cheaper and easier.
The inverter's AC output must conform to the conventional
power in the region in order to run locally available appliances. The
standard for AC utility service in North America is 115 and 230 volts at
a frequency of 60 Hertz (cycles per second). In Europe, South America,
and most other places, it's 220 volts at 50 Hertz.
Safety Certification
An inverter should be certified by an independent testing
laboratory such as UL, ETL, CSA, etc., and be stamped accordingly. This
is your assurance that it will be safe, will meet the manufacturer's
specifications, and will be approved in an electrical inspection. There
are different design and rating standards for various application
environments (buildings, vehicles, boats, etc.). These also vary from
one country to another.
Power Capacity
How much load can an inverter handle? Its power output is
rated in watts (watts = amps x volts). There are three levels of power
rating-a continuous rating, a limited-time rating, and a surge rating.
Continuous means the amount of power the inverter can handle for an
indefinite period of hours. When an inverter is rated at a certain
number of watts, that number generally refers to its continuous rating.
The limited-time rating is a higher number of watts that it
can handle for a defined period of time, typically 10 or 20 minutes. The
inverter specifications should define these ratings in relation to
ambient temperature (the temperature of the surrounding atmosphere).
When the inverter gets too hot, it will shut off. This will happen more
quickly in a hot atmosphere. The third level of power rating, surge
capacity, is critical to its ability to start motors, and is discussed
below.
Some inverters are designed to be interconnected or expanded
in a modular fashion, in order to increase their capacity. The most
common scheme is to "stack" two inverters. A cable connects the two
inverters to synchronize them so they perform as one unit.
Power Quality
Some inverters produce "cleaner" power than others. Simply stated, "sine wave"
is clean; anything else is dirty. A sine wave has a naturally smooth
geometry, like the track of a swinging pendulum. It is the ideal form of
AC power. The utility grid produces sine wave power in its generators
and (normally) delivers it to the customer relatively free of
distortion. A sine wave inverter can deliver cleaner, more stable power
than most grid connections.
How clean is a "sine wave"? The manufacturer may use the
terms "pure" or "true" to imply a low degree of distortion. The facts
are included in the inverter's specifications. Total harmonic distortion
(THD) lower than 6 percent should satisfy normal home requirements.
Look for less than 3 percent if you have unusually critical electronics,
as in a recording studio for example.
Other specs are important too. RMS voltage regulation keeps
your lights steady. It should be plus or minus 5 percent or less. Peak
voltage (Vp) regulation needs to be plus or minus 10 percent or less.
A "modified sine wave" inverter is less expensive, but it
produces a distorted square waveform that resembles the track of a
pendulum being slammed back and forth by hammers. In truth, it isn't a
sine wave at all. The misleading term "modified sine wave" was invented
by advertising people. Engineers prefer to call it "modified square
wave."
The "modified sine wave" has detrimental effects on many
electrical loads. It reduces the energy efficiency of motors and
transformers by 10 to 20 percent. The wasted energy causes abnormal heat
which reduces the reliability and longevity of motors and transformers
and other devices, including some appliances and computers. The choppy
waveform confuses some digital timing devices.
About 5 percent of household appliances simply won't work on
modified sine wave power at all. A buzz will be heard from the speakers
of nearly every audio device. An annoying buzz will also be emitted by
some fluorescent lights, ceiling fans, and transformers. Some microwave
ovens buzz or produce less heat. TVs and computers often show rolling
lines on the screen. Surge protectors may overheat and should not be
used.
Modified sine wave inverters were tolerated in the 1980s,
but since then, true sine wave inverters have become more efficient and
more affordable. Some people compromise by using a modified wave
inverter to run their larger power tools or other occasional heavy
loads, and a small sine wave inverter to run their smaller, more
frequent, and more sensitive loads. Modified wave inverters in renewable
energy systems have started fading into history.
Efficiency
It is not possible to convert power without losing some of
it (it's like friction). Power is lost in the form of heat. Efficiency
is the ratio of power out to power in, expressed as a percentage. If the
efficiency is 90 percent, 10 percent of the power is lost in the
inverter. The efficiency of an inverter varies with the load. Typically,
it will be highest at about two thirds of the inverter's capacity. This
is called its "peak efficiency." The inverter requires some power just
to run itself, so the efficiency of a large inverter will be low when
running very small loads.
In a typical home, there are many hours of the day when the
electrical load is very low. Under these conditions, an inverter's
efficiency may be around 50 percent or less. The full story is told by a
graph of efficiency vs. load, as published by the inverter
manufacturer. This is called the "efficiency curve." Read these curves
carefully. Some manufacturers cheat by starting the curve at 100 watts
or so, not at zero!
Because the efficiency varies with load, don't assume that
an inverter with 93 percent peak efficiency is better than one with 85
percent peak efficiency. If the 85 percent efficient unit is more
efficient at low power levels, it may waste less energy through the
course of a typical day.
Internal Protection
An inverter's sensitive components must be well protected
against surges from nearby lightning and static, and from surges that
bounce back from motors under overload conditions. It must also be
protected from overloads. Overloads can be caused by a faulty appliance,
a wiring fault, or simply too much load running at one time.
An inverter must include several sensing circuits to shut
itself off if it cannot properly serve the load. It also needs to shut
off if the DC supply voltage is too low, due to a low battery
state-of-charge or other weakness in the supply circuit. This protects
the batteries from over-discharge damage, as well as protecting the
inverter and the loads. These protective measures are all standard on
inverters that are certified for use in buildings.
Inductive Loads and Surge Capacity
Some loads absorb the AC wave's energy with a time delay
(like towing a car with a rubber strap). These are called inductive
loads. Motors are the most severely inductive loads. They are found in
well pumps, washing machines, refrigerators, power tools, etc. TVs and
microwave ovens are also inductive loads. Like motors, they draw a surge
of power when they start.
If an inverter cannot efficiently feed an inductive load, it
may simply shut down instead of starting the device. If the inverter's
surge capacity is marginal, its output voltage will dip during the
surge. This can cause a dimming of the lights in the house, and will
sometimes crash a computer.
Any weakness in the battery and cabling to the inverter will
further limit its ability to start a motor. A battery bank that is
undersized, in poor condition, or has corroded connections, can be a
weak link in the power chain. The inverter cables and the battery
interconnect cables must be big, and I mean REALLY big, perhaps the size
of a large thumb! The spike of DC current through these cables is many
hundreds of amps at the instant of motor starting. Follow the inverter's
instruction manual when sizing the cables, or you'll cheat yourself.
Coat battery connections with a protective coating to reduce corrosion.
Battery Charging Features
Backup battery charging is essential to most renewable
energy systems because there are likely to be occasions when the natural
energy supply is insufficient. Some inverters have a built-in battery
charger that will recharge the battery bank whenever power is applied
from an AC generator or from the utility grid (if the batteries are not
already charged). This also means that an inverter can be a complete
emergency backup system for on-grid power needs (just add batteries).
A backup battery charger doesn't have to be built into the
inverter. Separate chargers are, in some cases, superior to those built
into inverters. This is especially true in the case of low switching
frequency inverters, which tend to require an over-sized generator to
produce the full rated charge current.
The specifications that relate to battery charging systems
include maximum charging rate (amps) and AC input power requirements.
The best chargers have two or three-stage charge control, accommodation
of different battery types (flooded or sealed), temperature
compensation, and other refinements.
Be careful when sizing a generator to meet the requirements
of an inverter/charger. Some inverters require that the generator be
over-sized (because of low power factor, which is beyond the scope of
this article). Be sure to get experienced advice on this, or you may be
disappointed by the results.
Idle Power
Idle power is the consumption of the inverter when it is on,
but no loads are running. It is "wasted" power, so if you expect the
inverter to be on for many hours during which there is very little load
(as in most residential situations), you want this to be as low as
possible. Typical idle power ranges from 15 watts to 50 watts for a
home-size inverter. An inverter's spec sheet may describe the inverter's
"idle current" in amps. To get watts, just multiply the amps times the
DC voltage of the system.
Automatic On/Off
Inverter idling can be a substantial load on a small power
system. Most inverters made for home power systems have automatic
load-sensing. The inverter puts out a brief pulse of power about every
second (more or less). When you switch on an AC load, it senses the
current draw and turns itself on. Manufacturers have various names for
this feature, including "load demand," "sleep mode," "power saver,"
"autostart," and "standby."
Automatic on/off can make life awkward because a tiny load
may not trigger the inverter to turn on or stay on. For example, a
washing machine may pause between cycles, with only the timer running.
The timer draws less than 10 watts. The inverter's turn-on "threshold"
may be 10 or 15 watts. The inverter shuts off and doesn't come back on
until it sees an additional load from some other appliance. You may have
to leave a light on while running the washer.
Some people can't adapt to such situations. Therefore,
inverters with automatic on/off also have an always-on setting. With it,
you can run your low-power night lights, your clocks, fax, answering
machine and other tiny loads, without losing continuity. In that case, a
good system designer will add the inverter's idle power into the load
calculation (24 hours a day). The cost of the power system will be
higher, but it will meet the expectations of modern living.
Therefore, at I-CELL power we are committed to give a better value for your money with our product which come in different form and range. Our product range are inverters, deep cycle batteries which
are designed to assist in the generation of renewable power for use
within both homes, and office environments. They are packed with a range
of features, which ensures they are durable, sustainable, and
economically viable on the long run.
For Inquiries,
Contact I-cell Power
Call +2347030201132, +2348182186778
Email: Holyman4christ@gmail.com
Website: www.icellpower.com
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