The heart of any battery-based power system is an inverter. It converts the DC current from a battery bank into AC power that is used to run most household appliances rated at 230V AC. Inverters are also found in devices that operate off of DC such as power supply units (PSUs) and uninterruptible power supplies (UPS).
Inverters are available in a wide variety of sizes, types and brands. Selecting the right one for your application can be difficult. This article will cover the main factors to consider and provide some advice on selecting an inverter that is best for your needs.
Most renewable energy systems generate their electricity via DC current, which isn’t useful for home appliances. They need to be changed to the kind of electrical current that most people use, AC. Inverters do this work, changing the voltage and frequency as needed. They can be used with batteries, wind turbines, solar panels or a combination of these sources.
The basic design of an inverter uses semiconductor switches, called thyristors or SCRs to achieve its power handling capability. These are usually arranged in a three-phase configuration. The switch in each phase operates at each of the 60 degree intervals of a fundamental output waveform which is generated by a six-step square-wave. The resulting output is free of harmonic distortions that occur in conventional rectifiers.
Inverters have three ratings that describe how much power they can handle at various times. A continuous rating describes how much power the inverter can supply continuously, without overheating and shutting down. It is often written as a number of watts. The surge and spike ratings are important to consider as well when selecting an inverter.
Surge ratings refer to how much power the inverter can supply for short periods of time, a few seconds up to a few minutes. This is important because some appliances require a high surge to start functioning, such as pumps and refrigerators. If the inverter cannot handle this startup surge, it will not be able to function.
Inverter efficiency varies with load, which is why many inverters display a graph of their efficiency versus power level. It is important to look at this information carefully, to see what level of efficiency you can expect over a typical day with different loads.
All inverters are designed with safety features to ensure that they do not put too much strain on the batteries or overload the circuits. The safety features include sensing circuits that shut the inverter down if they detect a problem such as an overcharge of the batteries, a low battery state-of-charge or a fault in one of the internal components. They also have circuits that will shut the inverter down if there is a dangerously high temperature within the unit.
An inverter’s sensitive components must be protected against damage from surges from nearby lightning and static, as well as from spikes caused by motors. This is why they are generally encased in metal, and have heavy-duty wire connections. It is also important to use the right wire size when connecting an inverter. Using wire that is too small will cause the inverter to draw too many amps, which can cause it to overheat.
