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Specialized Machines

CNC/EDM and Other

Specialized Machine Operation

CNC, EDM, lasers, computers and other sophisticated equipment are operated by a digital controller. This controller is affected adversely by changes in line frequency and/or line-to-line voltage. GWM's catalog includes a thorough Application Guide for most types of equipment that are voltage sensitive.

Electrical Harmonics and Their Effect:

Digitally-driven equipment produces an electrical harmonic which creates heat in support equipment. Rotary converters used in these applications must be oversized to prevent electrical insulation breakdown in the converter two or three years into the installation. Use a ratio of 2 rotary kVA for each kVA of EDM or CNC.

Preventing Operating Problems of Voltage Drop:

A large rotary unit--relative to the CNC spindle motor--will provide stable voltage for CNC controls and XYZ axis motors during spindle acceleration or reverse braking, insuring successful operation of the equipment. Even though the rotary converter generates only one wire (T3) of 3-phase, the loads on that wire constitute two-thirds of the equipment's power, since both the B-to-C and A-to-C phasing voltage is derived from it. (Single-phase is the A-to-B phase voltage.) GWM's DIGI-Series converters are designed to produce ±5% voltages for this equipment. On special, we have provided CNC converters which met a manufacturer's requirement of ±3 volts! (See also "Light-Dimming and Phase Converters." and "Special Converter Sizing for CNC with Regenerative Loads."

Multiple Machine Operation:

Operating multiple CNC machines on the same converter is an iffy proposition, although many of our customers have done so with some success.

The best explanation is this: Some CNC will tolerate another motor starting and stopping during operation, some won't. The best recommendation I have is--try it! If it doesn't work, try advancing the power leads going to the machine that upsets regularly on the converter: specifically: move machine input lead No. 1 to terminal No. 2, lead No. 2 to terminal No. 3, and lead No. 3 to terminal No. 1. If that doesn't help, do it again. The third time you do so, of course you will be back to the original wiring configuration. Doing this will sometimes take a critical control circuit off of T3 (the manufactured phase) to permit multiple operation. In this writer's opinion use a separate converter for each CNC.