3. Rotary Phase Converter: A rotary converter amounts to a three-phase electric motor with some starting and control circuitry, all of which together acts as a generator producing nearly balanced three-phase electricity. The motor, called an idler motor, runs with no load on the supplied single-phase power. As described above, a three-phase motor can run on single-phase electricity at a reduced power output, but it cannot start on single-phase without additional help. Either some mechanical means such as a pull cord or a single-phase motor or some electric means - a static phase converter - are used to start the idler motor turning. Once it is turning, it is powered on two of it's three sets of windings by the single-phase power supply and, because an electric motor being spun is a generator, generates the third leg. Voila: three-phase power for the shop. This is an effective way to power multiple pieces of three-phase machinery , given an adequately sized rotary converter. One caveat applies to this type of system, which is that typically more than one load cannot be started at a time. Also, certain loads fall into different classes of "hardness to start", and require rotary converters oversized by a corresponding factor. For air compressors, considered one of the toughest starting loads, the recommended factor is at least 2. In my case, that meant a 10HP rotary converter, which is not even a little bit cheap.