8 Unidrive SP Low Voltage DC Installation Guide
www.controltechniques.com Issue Number: 1
2.4.2 Operation with a servo motor
The speed of a servo motor is limited based on the Ke (voltage constant) value as
shown in the example below: -
A Unidrive SP with a Low Voltage DC supply of 48V running a 3000rpm unimotor which
has a Ke value of 98V/Krpm.
• Calculate rpm per Volt.
• Calculate drive output voltage.
• From the above calculations the motor speed will be limited to:
When in Low Voltage DC operation the Unidrive SP may NOT be able to limit the speed
of a servo motor with an overhauling load.
If a permanent magnet motor is made to rotate at a high enough speed by an external
torque, the DC bus of the drive and its associated wiring could rise above the lower
voltage DC operating level.
WARNING
WARNING
1000rpm 98V⁄ 10.2rpm per volt=
48V 2()⁄ 34V=
10.2 34× 347rpm=
The calculation above gives an estimated value and does not take into account motor
volt drops etc.
NOTE
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