Rotary phase converter

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Contents 1 Definition 2 How RPCs work 3 Use of RPCs 4 See also 5 External links

[edit] Definition

A rotary phase converter, abbreviated RPC, is an electrical device that allows running three phase loads on Three-phase electric power using generator or utility supplied single phase electric power. The RPC can be connected directly to single phase power and will output three phase electrical power. The best types of RPC use actual three phase generators and apply power factor correction so the power output is balanced on all three legs.

Other homemade models attempt to generate a third leg by means of a rotating three phase induction motor called an idler. If the idler's rotor spins while two terminals are energized, it induces voltage in the third terminals that is shifted by +/- 120 degrees from the voltage between the first two terminals. The quality of three phase power generated by such a phase converter may or may not be satisfactory, depending on the following factors:

• Capacity of the phase converter (idler horsepower rating)
• Power level demands of the equipment being supplied. For instance, "hard starting" loads such as heavily loaded machinery or well pumps may have higher requirements than other loads rated at the same horsepower.
• Power quality demands of the equipment being supplied (CNC equipment may have more stringent power quality requirements than a welding machine )
• Use of capacitors to balance voltage between the three legs

[edit] How RPCs work

The main principles of home built RPC operation are as follows:

• Three phase induction motors have three contacts called "legs", usually numbered (arbitrarily) L1, L2, and L3. Their regular use under three phase power is to apply three phases to legs L1, L2, and L3 respectively, to convert electrical energy into mechanical power.

• A three phase induction motor can be run at two-thirds of its rated horsepower on single phase power applied to legs L1 and L2 (or any pair of legs), once spun up by some means.

• A three phase induction motor that is spinning under single phase power applied to legs L1 and L2, generated an electric potential (and can deliver unbalanced power through) leg L3.

• RPC's Built with three phase generators are a better choice than using an electric motor as they provide more balanced power output.

• Power factor correction is a very important consideration when building or choosing a RPC. Power factor correction is desirable because an RPC that has power factor correction will consume less amperage from the single-phase service supplying power to the phase converter and its loads. It is also better for the equipment that the power is supplied to.

Balanced voltage between the three legs of power is important for your equipment to have a long operational life. Unbalanced three phase can damage the equipment that it is meant to operate.

[edit] Use of RPCs

RPCs are used anywhere three phase devices need to be used, but only single phase power is available. Three phase machines cannot run on single phase power without a device to generate three phase power. Since prices (and quality) of used three phase machines are usually more favorable than those of their single phase counterparts, demand exists for phase converters. This is also true because there are almost no manufacturers of single phase electric motors of the larger sizes. In the larger HP sizes only three phase motors are available.

RPCs are sold by various vendors, but also are popular items to attempt to be made by do it yourselfers. Of practical importance to a do it yourselfer attempting to make a phase converter, is to understand the issues related to sizing and quality of three phase power produced.

Besides RPCs (the most popular technology used to convert phase), there are other technologies available today that may or may not perform as well as this proven technology.

[edit] See also

• Three-phase electric power
• Rotary converter
• Motor-generator
• Variable-frequency drive
• Frequency converter
• List of commercial phase converter manufacturers

[edit] External links

Please put all commercial links to page List of commercial phase converter manufacturers. Thanks.

• Jim Hanrahan's classic paper on making homemade RPCs
• Another article on making homemade RPCs
• How to Build a Phase Converter
• Article on Power Factor
• MC