Danfoss iC2-Micro Series - Brake Resistor Selection; Introduction; Brake Resistance Calculation

Design Guide | iC2-Micro Frequency Converters iC2-Micro Frequency Converters
l DC brake: An overmodulated DC current added to the AC current works as an eddy current brake (parameter P 5.7.3 DC Brake
Time≠0s).
3.7.3 Brake Resistor Selection
3.7.3.1 Introduction
To handle higher demands by generatoric braking, a brake resistor is necessary. Using a brake resistor ensures that the heat is absorbed
in the brake resistor and not in the drive.
If the amount of kinetic energy transferred to the resistor in each braking period is not known, calculate the average power based on the
cycle time and braking time. The resistor intermittent duty cycle is an indication of the duty cycle at which the resistor is active. A typical
braking cycle is shown in Figure 13.
T
ta
tc
tb
to ta
tc
tb
to ta
e30ba167.10
Load
Time
Speed
Figure 13: Typical Braking Cycle
The intermittent duty cycle for the resistor is calculated as follows:
Duty cycle=t
b
/T
t
b
is the braking time in seconds.
T = cycle time in seconds.
Table 12: Braking at High Overload Torque Level
Cycle time (s) 120
Braking duty cycle at 100% torque Continuous
Braking duty cycle at overtorque (150/160%) 40%
Danfoss offers brake resistors with duty cycles of 10% and 40%. If a 10% duty cycle is applied, the brake resistors are able to absorb brake
power for 10% of the cycle time. The remaining 90% of the cycle time is used for dissipating excess heat.
 NOTICE
Make sure that the resistor is designed to handle the required braking time.
3.7.3.2 Brake Resistance Calculation
The maximum allowed load on the brake resistor is stated as a peak power at a given intermittent duty cycle and can be calculated as:
where
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