12.3 Brake Resistor
12.3.1 Brief Introduction
Energy regenerated when a 3-phase AC motor is decelerated (the frequency is
reduced) is recovered and fed into the frequency converter. To prevent over
voltage of the frequency converter, an external brake resistor may be used. A
power transistor discharges the DC bus voltage energy (braking voltage thresh-
old at approx. 720 VDC for 400 V model, and 380 VDC for 200 V model) to the
brake resistor, and the energy is lost as heat.
● If a resistance lower than the recommended value (and no less
than the minimum resistance) is used, contact the agent or manu-
facturer for calculation of resistance power.
● Safety and flammability of surrounding conditions shall be consid-
ered. Keep all items 10 cm away from the brake resistor.
● A brake resistor can not work overload for a long time. 10 times
of rated load should not exceed 5 seconds.
● There could be smoking for the first use of the brake resistor as
its surface uses organic silicon, which is normal and does not af-
fect the performance of the brake resistor.
12.3.2 Brake Resistor Selection
Brake resistors with different power ratings are available to dissipate braking
energy when the frequency converter is in generator mode.
The adjacent tables list the optimal combination of frequency converter, brake
unit and brake resistor and the number of components required to operate one
frequency converter with respect to a given moderating ratio OT.
OT (On Time percentage)
Braking ratio
Tb Braking time
Tc Engineering cycle
time in application
Fig. 12-10: Braking ratio
For definition of typecode, see chapter 17.3 "Appendix 3: Type Cod-
ing" on page 242.
EFC 3600 Bosch Rexroth AG
Accessories
DOK-RCON03-EFC-3600***-IT03-EN-P
171/259
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