Appendix C. How to Select the Right AC Motor Drive｜VFD-EL-W
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C-2 General Precautions
Selecting an AC Motor Drive
1. When connecting the AC motor drive directly to a large-capacity power transformer (600 kVA or
higher), or when switching a phase lead capacitor, excess peak currents may occur in the power
input circuit and may damage the converter section. To avoid this, use an AC input reactor (optional)
before the AC motor drive mains input to reduce the current and improve the input power efficiency.
2. When using a special motor or when driving more than one motor in parallel with a single AC motor
drive, select the AC motor drive current to be 1.25x (sum of the motor rated currents).
3. The starting acceleration and deceleration characteristics of a motor are limited by the AC motor
drive rated current and the overload protection. Compared to running the motor D.O.L. (Direct On-
Line), you can expect a lower starting torque output with the AC motor drive. If a higher starting
torque is required (such as for elevators, mixers, tooling machines, etc.), use a higher capacity AC
motor drive or increase the capacities of both the motor and the AC motor drive.
4. When a fault occurs on the drive, a protective circuit is activated and the AC motor drive output is
turned off. The motor coasts to stop. For an emergency stop, use an external mechanical brake to
quickly stop the motor.
Setting Parameters
1. You can set the AC motor drive to an output frequency up to 400 Hz (less for some models) with the
digital keypad. Setting errors may create a dangerous situation. For safety, setting an upper limit
frequency function is strongly recommended.
2. High DC brake operating voltages and long operation time (at low frequencies) may cause
overheating of the motor. In that case, forced external motor cooling is recommended.
3. Motor acceleration and deceleration time is determined by motor rated torque, load torque, and load
inertia.
4. If you activate the stall prevention function, the acceleration and deceleration time is automatically
extended to a length that the AC motor drive can handle. If the motor must decelerate within a
certain time with a higher load inertia than the AC motor drive can handle in the required time, either
use an external brake resistor and/or a brake unit (depending on the model) to shorten deceleration
time only, or increase the capacity of both the motor and the AC motor drive.
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