Danfoss Recommended Brake Resistance Calculation - Danfoss iC2-Micro Series Design Manual

Design Guide | iC2-Micro Frequency Converters
As shown, the brake resistance depends on the DC-link voltage (U
Table 13: Threshold of the Brake Resistance
Size
3x380–480 V
The threshold can be adjusted in parameter P 3.2.2 Brake Chopper Voltage Reduce, with 70 V range.
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.
Make sure that the brake resistor can cope with a voltage of 800 V.

Danfoss Recommended Brake Resistance Calculation

3.7.3.3
Danfoss recommends calculating the brake resistance R
guarantees that the drive is able to brake at the highest braking torque (M
η is typically at 0.80 (≤7.5 kW/10 hp); 0.85 (11–22 kW/15–30 hp).
motor
η is typically at 0.97.
VLT
For iC2-Micro Frequency Converters, R
for drives ≤7.5 kW (10 hp) shaft output.
for drives as 11–22 kW (15–30 hp) shaft output.
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
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.
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
Brake active U
dc,br
770 V
NOTICE
NOTICE
according to the following formula. The recommended brake resistance
rec
at 150% braking torque is written as:
rec
NOTICE
.
min
NOTICE
NOTICE
).
dc
Warning before cutout
800 V
) of 150%.
br(%)
iC2-Micro Frequency Converters
Cutout (trip)
800 V
AJ402315027937en-000401 / 130R1239