ABB ACS880-M04 - Brake Resistors

174 Resistor braking
 Brake resistors
To select a brake resistor, calculate the following:
1. maximum power generated by the motor during braking
2. continuous power based on the braking duty cycle
3. braking energy during the duty cycle.
Pre-selected resistors are available from ABB as shown in the Brake resistors data
table on page 177. If the listed resistor is not sufficient for the application, a custom
resistor can be selected within the limits imposed by the internal brake chopper of the
ACS880-M04. 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:
WARNING! Never use a brake 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
• The braking energy must not exceed the energy dissipation capacity of the
selected resistor
• The resistor must be protected from thermal overload; see section Contactor
protection of drive on page 179.
(U
DC_BR
+ 30 V)
R
Pmax <
2