Lenze 6034 Brake chopper - Manual (Page 8)

6
4. Selection of the brake resistors
The resistance is calculated as follows:
Resistance [ ] =
(Threshold)2 [V]2
required peak power [W]
Ω
The value may not fall below the minimum resistance of the brake
chopper. Otherwise, the unit might be destroyed.
After having calculated the resistance, determine the rated
power of the brake resistor for cyclic braking operation.
For most applications, the brake time remains under 15s. In cyclic
braking operations, the relative ON period does not exceed max.
10%.
Rated power [W] =
ON period [s]
Cycle time [s]
required peak brake power [W]
⋅
For single or cyclic braking operations the heat capacity of the
brake resistor is calculated as follows:
Heat capacity kWs = ON period s peak brake power W
⋅
required
To avoid a thermal overload of the resistor, the heat capacity of the
brake resistor must be considered (if necessary please contact the
manufacturer).
Brake resistors may reach surface temperatures of up to 350°C.
Therefore the resistors mentioned above are equipped with
temperature monitoring. When using other brake resistors, an
appropriate overcurrent/overtemperature protection, e.g. thermal
overcurrent sensors, must be provided.
The thermostats of the brake resistors should be used to
disconnect the inverter from the mains in case of overheating (see
pages 9 and 10).