AutomationDirect SureServo2 Manual - Page 16

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Chapter 2: Installation

Calculation of the regenerative power when there is external torque and the motor does the

negative work.

1) Direction of motion of the object

2) Force direction of the motor

3) Regenerative power

Usually, the motor does positive work and the motor's torque direction is identical to the

rotation direction. However, in some instances, the motor's torque direction is opposite to

the rotation direction. This means the motor is doing negative work and the external power

is applied to the servo drive through the motor. For instance, if the external force direction

is identical to the rotation direction (such as vertical downward motion of the machine), the

servo system outputs more power to counterbalance the excessive external load (the weight

of vertical-mounted machine) in order to keep up with the specified target speed. In this case,

considerable power returns to the servo drive. When DC Bus cannot store more power, this

power is consumed by the regenerative resistor.

Example 2:

For a 400W motor (SV2L-204B) with an external torque load +70% of the rated torque (1.27

N·m), with rotation speed up to 3000 rpm, the required external regenerative resistance is:

So, a regenerative resistor of 560W and 40Ω is needed.

Page 2–16

3000 rev/min x 2 x π

2 x (0.7 x 1.27 Nm) x

= 560W

60 sec/min

SureServo2 User Manual – 1st Edition – 05/20/2021