Frequently Asked Questions

• What is an inverter?
  • An inverter takes DC power (from a battery or solar panel, for example) and converts it into alternating current (AC) "household" power for running electronic equipment and appliances.
• Q: Why are they called inverters?
  • A: Originally converters were large rotating electromechanical devices used to convert AC to DC. It is what you have to do if you don't have semiconductor or vacuum tube rectifiers. Essentially they combined a synchronous ac motor with a commutator so that the commutator reversed its connections to the ac line exactly twice per cycle. The results is ac-in dc-out (with a lot of switching noise thrown in). If you invert the connections to a converter you put dc in and get ac out. Hence an inverter is an inverted converter.
• Q: How is an inverter different than a UPS?
  • A: A UPS typically includes the inverter, battery and battery charger in one stand-alone unit. However, there are UPSs that use external batteries, and PowerStream has made inverters with battery chargers, so the differences blur as features proliferate.
    
    UPSs also can have communication with the equipment that it is powering, which lets the equipment know that it is operating on standby, giving it shutdown warning, or communicating with the human in the loop. Inverters typically don't have this communication.
• Q: What if I want a DC output to run such things as a laptop from a car cigarette lighter, or telephone equipment at -48 volts?
  • A: Then you want a DC/DC converter. PowerStream has many DC/DC converters just for those purposes. /dcdc.htm
• Q: What is the difference between sine wave and modified sine wave?
  • A: Alternating current (AC) has a continuously varying voltage that swings from positive to negative. This has great advantages in power transmission over long distances. Power from your power company is carefully regulated to be a perfect sine wave, because that is what naturally comes out of a generator, and also because sine waves radiate the least amount of radio power during long distance transmission.
    
    On the other hand, a sine wave is expensive to make in an inverter, and many sine wave techniques use heavy, inefficient transformers. The most inexpensive way to make AC is to switch the DC on and off--a square wave. A modified sine wave is scientifically designed to simulate a sine wave in the most important respects so that it will work for most appliances. It consists of a flat plateau of positive voltage, dropping abruptly to zero for a while, then dropping again to a flat plateau of negative voltage, back to zero for a while, then returning to the positive voltage. This pause at zero volts puts more power into the 60HZ fundamental than a simple square wave does, so it is called "modified sine wave" instead of "square wave." Because the MOSFETs only have to turn completely on and completely off the dissipate he least amount of heat for the power generated, and so smaller semiconductors and heat sinks are needed than if you were trying to generate a real sine wave.
• Q: Can I use a modified sine wave inverter for my medical equipment?
  • A: For Medical equipment, oxygen generators, etc. talk to the manufacturer of the equipment. PowerStream inverters are never tested or rated with medical equipment, and we don't guarantee that they will work to save your life. For such applications please find inverters that are rated and tested for such applications.
• Q: What about square wave inverters?
  • A: These old-fashioned inverters are the cheapest to make, but the hardest to use. They just flip the voltage from plus to minus creating a square waveform. They are not very efficient because the square wave has a lot of power in higher harmonics that cannot be used by many appliances. Synchronous motors, for example, use the 60Hz component and turn the rest of the frequencies into heat. The modified sine wave is designed to minimize the power in the harmonics while still being cheap to make.