ABB ACS850 series, Hardware Manual

Page: 103 / 120

Resistor braking
103
Resistor braking
What this chapter contains
This chapter describes how to select, protect and wire braking choppers and
resistors. The chapter also contains the technical data.
Braking choppers and resistors with the ACS850-04
Braking choppers
ACS850-04 (frame A…D) drives have a built-in braking chopper as standard
equipment to handle the energy generated by a decelerating motor.
When the braking chopper is enabled and a resistor connected, the chopper will start
conducting when the DC link voltage of the drive reaches 780 V. The maximum
braking power is achieved at 840 V.
Braking resistor selection
To select a braking resistor:
1. Calculate the maximum power generated by the motor during braking.
2. Calculate the continuous power based on the braking duty cycle.
3. Calculate the braking energy during the duty cycle.
Pre-selected resistors are available from ABB as shown in the table below. If the
listed resistor is not sufficient for the application, a custom resistor can be selected
within the limits imposed by the internal braking chopper of the ACS850-04. The
following rules apply:
• The resistance of the custom resistor must be at least R
min
. The braking power
capacity with different resistance values can be calculated from the following
formula
where UDC equals 840 V.
WARNING! Never use a braking resistor with a resistance below the value specified
for the particular drive type. The drive and the chopper are not able to handle the
overcurrent caused by the low resistance.
• The maximum braking power must not exceed P
brmax
at any point
• The average braking power must not exceed P
brcont
P
max
<
U
DC
R
2