Inverters
The efficiency of an inverter has to do with how well it converts the DC voltage into AC. This usually ranges from 85% to 95%, with 90% being about average.
However, there is more to the story. Efficiency ratings are usually given into a resistive load (basically something like a light bulb or electric heater). When running such things as motors, the efficiency actually breaks down into two parts - the efficiency of the inverter, and the efficiency of the
waveform. Waveform efficiency means that most motors and many electronic appliances run better and use less power with a sine wave. Typically, an electric motor (such as a pump or refrigerator) will use from 15% to 20% more power with a modified sine wave than with a true sine wave. When choosing an inverter based on efficiency, you should also consider what you are going to be running.
A 90% efficient modified sine wave inverter is not 90% when running a compressor motor, for example, because electric motors are less efficient. They use about 20% more power on a modified sine wave.
Inverters are also much less efficient when used at the low end of their maximum power. For example, using a 1000 watt inverter to power a 20 watt radio may actually be using 30 to 40 watts from the battery, as the inverter itself is eating up a lot just to run. Most inverters are most efficient in the 30% to 90% power range.
Linear DC-Dc converters
Linear regulators drop the input voltage to a lower output voltage. They are inefficient, as they convert the dropped voltage into heat dissapation.
Linear regulator are inexpensive, reliable, and much simpler than switching regulators. Linear regulators also can provide a very quiet output voltage, and are much more suited to powering sensitive analog circuits.
However, unlike switching DC-DC converters, linear regulators cannot generate:
- Higher voltages than their input
- Large currents (due to excess heat)
Switched mode
Electronic switch-mode DC to DC converters convert one DC voltage level to another, by storing the input energy temporarily and then releasing that energy to the output at a different voltage. The storage may be in either magnetic components (inductors, transformers) or capacitors. This conversion method is more power efficient (often 80% to 98%) than linear voltage regulation (which dissipates unwanted voltage as heat). This efficiency is beneficial to increasing the running time of battery operated devices. Drawbacks of switching converters include cost, complexity and electronic noise .
