Lenze MDxMA-MHxMA-MFxMA-MDERA-MHERA Three-phase AC motors - Manual (Page 29)

Mechanical installation
Spring−applied brakes
5
l
29 BA 33.0005−EN 2.0
5.5 Spring−applied brakes
Important notes
As an option, the motors can be fitted with a brake. The installation of brakes (in or on the
motor) increases the length of the motor.
)
Note!
The brakes used are not fail−safe because interference factors, which cannot
be influenced (e.g. oil ingress), can lead to a reduction in torque.
The brakes serve to hold the axes at standstill or in the deenergised state.
They operate according to the closed−circuit principle, i.e. the brake is closed in the
deenergised state. The brakes for DC supply can be fed with a bridge−rectified DC voltage
(bridge rectifier) or with a smoothed DC voltage. The permissible voltage tolerance is
± 10 %.
If long motor supply cables are used, pay attention to the ohmic voltage drop along the
cable and compensate for it with a higher voltage at the input end of the cable.
The following applies to Lenze system cables:
U *
+ U
B
)
ƪ
0.08
W
m
@ L @ I
B
ƫ
U* [V] Resulting supply voltage
U
B
[V] Rated voltage of the brake
l [m] Cable length
I
B
[A] Rated current of the brake
(
Stop!
If the brake is not supplied with the correct voltage (see nameplate), the brake
is applied and may be overheated and destroyed by the motor that possibly
continues to rotate.
The shortest operating times of the brakes are achieved by DC switching of the voltage and
a suppressor circuit (varistor or spark suppressor). Without suppressor circuit, the
operating times may increase. A varistor/spark suppressor limits the breaking voltage
peaks. It must be ensured that the power limit of the suppressor circuit is not exceeded.
This limit depends on the brake current, brake voltage, disengagement time and the
switching operations per time unit.
Furthermore, the suppressor circuit is necessary for interference suppression and also
increases the service life of the relay contacts (external, not integrated in the motor).
For permissible operating speeds and characteristics, please see the respective valid motor
catalogue. Emergency stops at higher speeds are possible, but high switching energy
increases wear on the friction surfaces and the hub.
(
Stop!
The friction surfaces must always be free from oil and grease because even
small amounts of grease or oil will considerably reduce the braking torque.
The formula below provides a simplified way to calculate friction energy per switching
cycle which must not exceed the limit value for emergency stops that depends on the