Rotary Converters
Technical Information


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In a home workshop, farm, garage or small business environment there is often a requirement for the operation of machinery driven by three phase induction motors where only a single phase electricity supply is available.

The Rotary Converter provides an artificial means by which a three-phase motor can be operated from a single-phase supply thereby offering a cost-effective solution to this dilemma. In most instances, no modification to the machine is necessary.

The Rotary Converter is particularly suited to the multi-motor, multi-operator environment. Multi-motor applications can be accommodated up to the maximum loading of the converter provided that the specified maximum single motor load is not exceeded.

The Rotary Converter is often operated in conjunction with machine tools, however it is also suitable for applications where equipment has a heavy starting load or is subjected to an abnormal surge current. Vehicle Hoists, Compressors, Pumps and Extractor Fans fall into this latter category. It should be noted that converters are designed for applications with a cyclic duty. Please seek advice for continuous duty applications.

Currently, eight sizes of Rotary Converter are available designed to operate single motor loads up to 18.5kW (25hp) and multi-motor loads up to 22.0kW (30hp).

For applications with single motors in excess of 18.5kW (25hp) or combinations of motors in excess of 22kW (30hp), please seek further advice.

A Static Converter can also be considered for single motor applications. This style of converter is typically used in a single operator environment where only one machine is used at a time.

TECHNICAL DATA
The converter offers no inherent overload protection to either the circuit cable or the driven machinery. Adequate overload protection for both the motors in the driven machinery and the supply circuit to the converter is the responsibility of the customer. The customer should also ensure that the electricity system and cable supplying the converter is of sufficient capacity to allow the motor to start without causing undue supply disturbances as a consequence of voltage drop.

TECHNICAL NOTES
The full load running current (flc) of an induction motor operating on a single-phase supply is approximately 4 amps per hp. When operated in conjunction with a Rotary Converter, the starting current of a three-phase motor is limited to approximately 3 times its flc. This is significantly lower than the motor starting current of an equivalent sized single-phase motor, which would typically draw between 6-8 times its flc.

As the starting characteristics of a three-phase motor supplied by a converter are similar in nature to Star/Delta starting on a three-phase supply, significant reductions in starting torque are experienced when compared with direct on line starting on a three-phase supply.

Generally when machinery is operated in conjunction with a Rotary Converter direct on line starting is recommended. For machinery fitted with a Star/Delta starter, the period in the star connection should be set as short as possible to ensure a successful start. This is not the case when machinery is operated on a mains three-phase supply.

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