Braking operation
11−1
L EDB82MV752 EN 5.2
11 Braking operation
11.1 Braking operation without additional measures
In order to brake low masses you can parameterise the "DC injection brake DCB" ( 7−30) function.
11.2 Braking operation with external brake resistor
Larger moments of inertia or longer generator−mode operation require an external brake resistor. It
converts mechanical energy into heat.
The brake transistor integrated in the controller switches the external brake resistor in addition when
the DC−voltage exceeds a threshold. It can thus be avoided that the controller sets "overvoltage"
and pulse inhibit and forces the drive to coast to standstill. External brake resistors ensure braking
operation at any time.
11.2.1 Selection of brake resistors
The Lenze brake resistors recommended in the tables are matched to the corresponding controller
(with regard to 150 % of regenerative power). They are suitable for most of the applications.
For special applications, e.g. centrifuges, the suitable brake resistor must meet the following
requirements:
Brake resistor Application
Criterion with active load with passive load
Continuous braking power [W]
P
max
h
e
h
m
t
1
t
cycl
P
max
h
e
h
m
2
t
1
t
cycl
Thermal capacity [Ws]
P
max
h
e
h
m
t
1
P
max
h
e
h
m
2
t
1
Resistor [Ω]
R
min
R
U
DC
2
P
max
h
e
h
m
Active load Can move by itself without any influence from the drive
(e.g. unwinder)
Passive load Stops by itself without any influence from the drive
(e.g. horizontal travelling drives, centrifuges, fans)
U
DC
[V] Switching threshold for brake transistor from C0174
P
max
[W] Maximum braking power defined by the application
e
Electrical efficiency (controller + motor)
Guide values: 0.54 (0.25 kW) ... 0.85 (11 kW)
m
Mechanical efficiency (gearbox, machine)
t
1
[s] Braking time
t
cycl
[s] Cycle time = Time between two subsequent braking cycles (= t1 + dead time)
R
min
[Ω] Lowest permissible brake resistance (see rated data of the integrated brake transistor)
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