Danfoss iC2-Micro Series - Danfoss Recommended Brake Resistance Calculation

As shown, the brake resistance depends on the DC-link voltage (U
dc
).
Table 13: Threshold of the Brake Resistance
Size Brake active U
dc,br
Warning before cutout Cutout (trip)
3x380–480 V 770 V 800 V 800 V
The threshold can be adjusted in parameter P 3.2.2 Brake Chopper Voltage Reduce, with 70V range.
 NOTICE
The greater the reduction value, the faster the reaction to a generator overload. Should only be used if there are problems with
overvoltage in the DC-link voltage.
 NOTICE
Make sure that the brake resistor can cope with a voltage of 800V.
3.7.3.3 Danfoss Recommended Brake Resistance Calculation
Danfoss recommends calculating the brake resistance R
rec
according to the following formula. The recommended brake resistance
guarantees that the drive is able to brake at the highest braking torque (M
br(%)
) of 150%.
η
motor
is typically at 0.80 (≤7.5kW/10hp); 0.85 (11–22kW/15–30hp).
η
VLT
is typically at 0.97.
For iC2-Micro Frequency Converters, R
rec
at 150% braking torque is written as:
for drives ≤7.5kW (10hp) shaft output.
for drives as 11–22kW (15–30hp) shaft output.
 NOTICE
The resistance of the brake resistor should not be higher than the value recommended by Danfoss. For brake resistors with
a higher ohmic value, the 150% braking torque may not be achieved because the drive might cut out for safety reasons. The
resistance should be bigger than R
min
.
 NOTICE
If a short circuit in the brake transistor occurs, prevent power dissipation in the brake resistor by using a mains switch or contactor
to disconnect the mains for the drive. The drive can control the contactor.
 NOTICE
Do not touch the brake resistor because it can get hot during braking. To avoid fire risk, place the brake resistor in a secure
environment.
34 | Danfoss A/S © 2024.08 AJ402315027937en-000401 / 130R1239
Design Guide | iC2-Micro Frequency Converters iC2-Micro Frequency Converters