Building a Three Phase Converter METAL WEB （建立三相变换器金属网络）.pdfVIP

Building an Auto-Start Rotary Three Phase Converter by: Matt Isserstedt Disclaimer: Electrical wiring is inherently dangerous. No warranties are issued or implied about the safety or success of this system. What I built is an automated-start version of a standard rotary phase converter with 3hp capacity. While the auto-start feature is not required and thus adds a little complexity, the general construction rules of a rotary phase converter still apply. One major benefit of the auto-start feature appears when it comes to expansion; I can start the converter from anywhere I can install another start/stop button. General Rotary Converter Principles Sizing The general rule of thumb is that you can start and run a motor equal to the hp of your idler. My largest machine tool motor is 3hp and thus I bought a spare 3hp, three-phase motor to be my idler. The frame spec and shaft condition of the idler is not important so a surplus motor can be used. Static Conversion To get to rotary conversion we must first understand static conversion. The idler motor in the rotary converter starts and runs in a static mode. In a typical household, 220 VAC exists on double-pole breakers. We say this has “2 legs”. A three-phase motor will RUN on only two of its three legs. Otherwise said, with single-phase power we can run a three-phase motor. The issue then becomes how to start said motor, because a three-phase motor will NOT START on single phase by itself. Motor Starting There are two ways to start a motor that is going to be run with static phase conversion. Most basically, we can start the three-phase motor mechanically by spinning its shaft with an outside source of power. This is typically a belt- drive arrangement from a smaller single-phase “pony” motor, and requires lots of design and safety considerations. The second, and simpler method is to start the motor electrica