Wireless+Networking+in+the+Developing+World_Part13

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Unformatted text preview: Converters The regulator provides DC power at a specific voltage. Converters and invert- ers are used to adjust the voltage to match the requirements of your load. DC/DC Converters DC/DC converters transform a continuous voltage to another continuous voltage of a different value. There are two conversion methods which can be used to adapt the voltage from the batteries: linear conversion and switch- ing conversion . Linear conversion lowers the voltage from the batteries by converting excess energy to heat. This method is very simple but is obviously inef f cient. Switching conversion generally uses a magnetic component to temporarily store the energy and transform it to another voltage. The resulting voltage can be greater, less than, or the inverse (negative) of the input voltage. The ef f ciency of a linear regulator decreases as the difference between the input voltage and the output voltage increases. For example, if we want to convert from 12 V to 6 V, the linear regulator will have an ef f ciency of only 50%. A standard switching regulator has an ef f ciency of at least 80%. DC/AC Converter or Inverter Inverters are used when your equipment requires AC power. Inverters chop and invert the DC current to generate a square wave that is later f ltered to approximate a sine wave and eliminate undesired harmonics. Very few inverters actually supply a pure sine wave as output. Most models available on the market produce what is known as "modi f ed sine wave", as their volt- age output is not a pure sinusoid. When it comes to ef f ciency, modi f ed sine wave inverters perform better than pure sinusoidal inverters. Be aware that not all the equipment will accept a modi f ed sine wave as volt- age input. Most commonly, some laser printers will not work with a modi f ed sine wave inverter. Motors will work, but they may consume more power than if they are fed with a pure sine wave. In addition, DC power supplies tend to warm up more, and audio ampli f ers can emit a buzzing sound. Aside from the type of waveform, some important features of inverters include: • Reliability in the presence of surges. Inverters have two power ratings: one for continuous power, and a higher rating for peak power. They are capable of providing the peak power for a very short amount of time, as when starting a motor. The inverter should also be able to safely interrupt Chapter 7: Solar Power 231 itself (with a circuit breaker or fuse) in the event of a short circuit, or if the requested power is too high. • Conversion ef f ciency. Inverters are most ef f cient when providing 50% to 90% of their continuous power rating. You should select an inverter that most closely matches your load requirements. The manufacturer usually provides the performance of the inverter at 70% of its nominal power....
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