Solar Ray !  The Most Reliable Name in Solar! Now serving Colorado, the Rockies, the South West, & beyond!

Power to the People!  Renewable Energy and Solar Power for Colorado, the Rockies, the American South West, and beyond!
SolarRay Power Boards
Official direct supplier of MidNite Solar products
Direct Supplier
of MidNite Solar
Click for the BBB Business Review of this Contractors - Solar Energy in Denver CO
& Control

Note: the following charts list battery based inverters only.

Retail prices shown,
Link to Catalog

*These are the Exeltech factory ratings--we've found these ratings to be a little high. The Exeltech XPs do not like to be pushed to their upper limits (they blow their (special order) input fuses very readily). They really shouldn't be subjected to surge loads at all. They should be used only for certain, limited loads, such as stereos or computers. For a general household pure-sine inverter, use an OutBack.

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.


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.


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.

It could require the entire output of a 120 watt panel just to keep the inverter on 24 hours a day.
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

n 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.)

We recommend this type of controller only with generators designed to be operated this way, the larger stationary type, not with smaller, portable generators that simply have an electric starter--they are too problematic when used with auto start.
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.


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.

In our opinion, no matter how extensive an inverter's meter, there is no substitute for a Trimetric Meter--for all the critical information it provides for system monitoring and trouble shooting. With the majority of the systems we design and install, a Trimetric is included, regardless of inverter. Link to Meters Page

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.


Link to Catalog for Current Listings.

Back to First Inverter Page