Note: the following charts list
battery based inverters only.
Retail prices shown,
Link to Catalog
WATTAGE:
A watt is a unit of power.
This power rating is the most basic measure of an inverter's capacity. It tells
how much power the inverter is able to produce--i.e., what loads
the inverter is capable of operating. There are two very different measurements
of wattage that are important:
CONTINUOUS
WATTS: This is the
amount of power the inverter can provide on a continual basis, 24 hours a day,
7 days a week. To determine what continuous wattage you need, add up all the continuous
loads that might be on at one time.
SURGE
WATTS: This is the
amount of power the inverter can deliver on an instantaneous, short term basis.
When first turned on many electrical devices need much more power to start than
they do in normal operation--especially those with electric motors, such as well
pumps, vacuum cleaners, and circular saws. Most electric motors require 4-6 times
the amount of power required while running just in order to start running.
This spike of electricity drawn by the load is called a surge.
DC VOLTS IN: This tells
what DC voltage an inverter
is designed to operate on--in other words, what voltage the battery bank and charge
controller provide to the inverter. The most common
are 12, 24, and 48 volts. (See battery wiring for
different voltages)
AC VOLTS OUT:
This tells what AC voltage
an inverter is designed to produce. Most inverters produce 120 VAC only, so that
in order to get 240 VAC (to run a well pump, for example) one would need to stack
two (or more) inverters together. However, Magnum Energy is now producing two
models that produce 120/240 VAC, making inverter stacking unnecessary in some
cases.
Top
BATTERY CHARGER: Most inverters
designed for battery-based systems ("inverter/chargers") will have one
of these built in. It's function is not to charge from DC sources, such as solar
panels, as one might think--that function is handled by a charge
controller. The purpose of a battery charger is to charge
from an AC source, such as a back-up generator or the grid, when battery voltage
goes too low.
The
best battery chargers are known as 3-stage chargers,
the stages of which are commonly called bulk, absorb, and float. It isn't important
to discuss the difference between these three stages here, but it is important
to know that there is a big difference between a 3-stage charger and a 1-stage,
simple on/off type, which is common to cheap automotive battery chargers.
The Outback Inverters feature a 4th stage which is a refloat, that does a better
job of maintaining batteries in grid tie/ backup mode. This mode doesn't really
come into play in off grid use.
All
Inverters with built-in battery chargers also have built-in automatic
transfer switches. When AC power from a back-up generator
or the grid is fed to an inverter/charger to charge the battery bank, the transfer
switch allows that AC power to pass through the inverter directly to it's AC output,
while using the rest of the power for battery charging. When the inverter senses
the AC input power, it switches automatically into pass-through mode, then back
again once the AC input power stops. This is the role of the automatic transfer
switch. It does its job so fast, 10-30 milliseconds, that the power seems continuous--generally,
computers and CD players don't even hiccup.
The
automatic transfer switch allows the inverter and battery bank to be used as a
household UPS (Uninterruptible
Power System) when hooked up to grid power. Basically the house would run off
grid power all the time, except in the case of a black out, when the automatic
transfer switch would seamlessly switch to inverter power, thus keeping the lights
on and the computer running.
The
battery chargers built-into the inverters we sell also have temperature compensation
functions, which vary the charging parameters according to the temperature in
the battery compartment. This is important for battery banks that are subjected
to wide temperature fluctuations or extremes.
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Sleep Mode: This feature goes
by many names: search, standby, etc. When in this mode, the inverter
waits to provide power until it senses a load. So, when all loads are turned off
and power is not needed, the inverter shuts almost totally down, thereby reducing
the continuous drain of the inverter's idling (which can be as much as 20 watts)
to just a watt or two. Then when something is turned on, the inverter will "wake
up" and provide power as long as there is a load that needs it.
In practice, however, many people of the hands-off persuasion
don't like to deal with what can become the hassle of working with search mode.
It is not as simple as described above. Since there is an threshold at which the
inverter wakes up, small loads, such as portable radios, may not draw enough power
to reach this threshold and wake up a sleeping inverter. There is also a slight
but noticeable lag between the time a load is turned on and when the inverter
senses the load and reacts; some people find this too annoying. See:
"To Sleep or Not to Sleep" Table
In addition, phantom loads,
such as answering machines and oven clocks (which are designed to remain on all
the time) will be shut off when an inverter sleeps. If a person does not want
to change his/her lifestyle enough to eliminate phantom loads, search mode will
be of no use. Larger systems have enough extra capacity to leave the inverter
on all the time and not bother with search mode. (Yes, search mode can be disabled
and the inverter simply switched on.)
GENERATOR AUTO START:
Some higher-end inverters have optional controllers which can automatically start
a generator when back-up power is needed, then shut it down when the batteries
have been recharged sufficiently.
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AUXILIARY LOAD CONTROL: Some
higher-end inverters can also start and stop auxiliary loads, like battery box
vent fans and surplus diversion loads
("dump loads"), depending on system voltage.
EXPANDABILITY: Higher-end inverters
often have the ability to be linked together ("stacked") for
more power. By stacking two identical inverters you can get twice the wattage
at the same output voltage, 120VAC--or you can get 240VAC. The OutBack FX and
VFX series inverters can even be combined to get 3-phase, 208VAC. Xantrex TR inverters
can be stacked in pairs; whereas up to ten of the OutBacks can be stacked, with
the use of a HUB controller, for up to 20kW of power.
METER:
Some inverters come with built-in LCD meters, displaying battery voltage, amperage
draw and what not--a few of which are quite extensive (like the Xantrex/Trace
SW and SW+). More commonly, a few indicator LEDs provide basic information.
NOISE:It is no secret--inverters can be noisy.
Many produce some degree of buzz, and cooling fans also can be annoying. The loud
buzz of the Xantrex/Trace PS inverters, for example, has been likened to the roar
of a lawn mower (a bit of an exaggeration, but you get the idea). We recommend
that power boards not be installed in one's living space and instead that they
have their own room or closet. (There are specific code requirements for such
spaces, so call before you build.) The OutBack FX series is completely sealed
and has no noticeable buzz. The FX-T series is fan cooled, so the sound of the
fan cycling on and off is the only sound it produces. The smaller Exeltech XPs
(the 125 and 250) have no fans and are very quiet. The Xantrex TR has a significant
buzz. Top
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