The Rotary Converter is designed to supply full running current to a three-phase motor normally providing it with full running torque. However, most motors will draw five times their running current during start-up. When used at its maximum HP rating the Rotary Converter cannot deliver the full (5 times) starting current to the motor and therefore cannot provide full starting torque. For heavy start-up loads a larger converter should be used. Below are the minimum size recommendations for various applications.
NOTE: You can always use a larger Rotary Converter than the HP of the motor. There is no minimum load requirement for the Rotary Converters. Some customers will install a Rotary Converter larger than they need to accommodate any future additions to their equipment. However, in some cases when a machine motor is significantly smaller than the HP rating of the converter, it may be necessary to add a Phase-A-Matic™ Voltage Stabilizer.
Sizing For Load Types
1. Motor Loads
May be used up to the HP rating of the converter. This applies to machinery with American made motors and which start with no load such as mills with step-pulley speed change, lathes with a clutch, sewing machines, and so forth.
NOTE: For instant reversing (as for rigid tapping), size according to TYPE 3 LOADS. Many restrictions apply. Most applications require sizing the converter a minimum of 50% larger (see all load types). Contact Phase-A-Matic, Inc. to verify load type.
These include domestic & European lathes without a clutch, some pumps, wheel balancers, paper cutters, flywheel driven equipment, blowers, woodworking band saws, dough mixers, meat grinders, motors rated below 1000 RPM, etc. Use a converter with HP rating of at least 50% larger than HP of the motor.
NOTE: For instant reversing (as for rigid tapping), size according to TYPE 3 LOADS
These include Design "E" motors, Taiwanese, Chinese, Mexican motors, pumps starting under load, etc. Also, any motor that is used to instant reverse as in rigid tapping, use a converter with twice the HP rating of the motor.
Use a converter with three times the HP rating to run Brazilian made WEG motors. Size the converter three times larger to run laundry extractors, hoists, elevators, etc. This type of equipment can be extremely heavily loaded on start up. Consult Phase-A-Matic for possibility of successfully using a converter sized less than three times on these machines.
Hydraulic pumps, which come under a momentary load during use, will be loaded well beyond their rated HP for the brief period of maximum PSI. Examples includes bailers, compactors, paper cutters, shears, pumps, etc. The HP of the converter must be at least as high as the actual HP developed by the motor. To calculate the HP developed, you must first find the actual amperage drawn during maximum PSI. This is different from the rated amps of the motor. Next you would divide the maximum amperage by 2.8 to find the actual HP being developed by the motor. That figure is the minimum size converter to be used. Example: A 10 HP compactor with a motor rated at 28 amps but draws a peak of 40 amps momentarily at maximum compression. Divide 40 by 2.8 = 14.3 HP being developed, use model R-15 Rotary Converter.
2. Resistive Loads
Resistive loads must use the Rotary type converter, the Static type should never be used because it would be damaged. There are two methods to determine the HP of the converter to be used. One method is to take the amperage rating of the equipment and divide by 2.8 to find the equivalent HP. The other method is to take the KW rating and multiply times 1.34 or divide by .75 to find the equivalent HP of the equipment.
3. Computer, Rectifier & Transformer Loads
Transformers and electric equipment (welders, lasers, EDM machines, CNC equipment, computers, plating rectifiers, power supplies, etc.) can operate on the Rotary Converter. Use the same formula as for resistive loads to determine the proper size converter to use.
If a 4-wire wye input is required (all lines equal voltage to ground), a three phase delta-to-wye isolation transformer must be installed between the converter and the equipment to change the delta power to wye power.
4. Multiple Motor Applications
Due to the high in-rush current required to start a motor (5 to 10 times the normal running current), most applications require sizing the HP of the Rotary Converter 50% larger, or more than the horsepower of the largest motor, or any combination of motors started at exactly the same time. The first motor started, if not running heavily loaded, generates additional 3-phase power back into the circuit. You can then run additional motors, provided they are not running heavily loaded and not all started at the same time. A maximum of up to 3 times the HP rating of the Rotary Converter can run at the same time, if not heavily loaded, and not started simultaneously. For example, a 10 HP Rotary Converter potentially could run motors totaling up to 30 HP. Contact factory for verification of sizing.