Technical information

23
Installation
• The AC power is derived from an open delta, earthed midpoint power source.
A “constant voltage” ferro-resonant transformer is not recommended under any
circumstances. This type of transformer is intended only for constant load applications,
and can cause high voltage surges during power up.
If an input transformer is being used, the size of the transformer will be determined by the
application requirements of the system. The easiest way to size a transformer is to calculate
the continuous wattage rating of the amplifier and choose the transformer size accordingly.
For purposes of this explanation, the wattage and transformer KVA rating will be used
interchangeably.
If your application has multiple axes, each of the drive’s KVA requirements must be added
together to determine the proper transformer size. This method may oversize the transformer
in a system where all of the drives may not operate at the same time.
Failure to follow safe installation guidelines can cause death or serious injury. When an
FX drive is powered up, there is a large inrush current or surge current caused by the
capacitance of the drive. This inrush current can cause the voltage to drop enough to cause
positioning drive malfunctions. Because of this, the minimum size transformer for each
axis is .5 KVA. If there are three axes of motion control on a system, the minimum size
transformer is 1.5 KVA.
The following parameters are required in order to correctly calculate and select the proper
transformer size:
• The maximum motor speed in RPM that will be required for the motion profile.
• The average torque in lb-ins required for the motion profile demanding the highest torque.
This average value does not include dwell time.
The calculation to determine the KVA rating of the transformer is as follows:
Single Phase
RPM x T(avg) x 0.018/1000 = KVA
Three Phase
RPM x T(avg) x 0.01182/1000 = KVA
Where RPM is maximum required motor speed in RPM and T(avg) is the average torque
required in lb-in.
After calculating the transformer size, select the correct transformer for the application. If the
calculated transformer size is not a “standard” size, then the next larger size should be used.
It is better to oversize than to undersize. If the KVA rating is too small, the available voltage