Lenze 8400 protec - Selection of the Brake Resistors

Braking operation
Braking operation with external brake resistor
Selection of the brake resistors
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EDS84DPS424 EN 5.0
9.2.1 Selection of the brake resistors
To decelerate greater moments of inertia or with a longer operation in generator mode an
external brake resistor is required. It converts braking energy into heat.
The brake resistors recommended in the accessories chapter are designed to tolerate a
regenerative power of approx. 1.5 times the normal value. The cycle time of the brake
resistors is 150 s and includes a braking time of max. 15 s and a recovery time (pause) of
min. 135 s.
ƒ The brake resistors are equipped with a thermostat each (potential−free NC contact,
switching capacity: AC 250V, 0.5A).
ƒ To increase the power, brake resistors can be connected in parallel or in series.
– The resistance for the controller must not fall below the lowest permissible value.
– The thermostat of several brake resistors at a controller must always be connected
in series.
 Note!
The 8400 protec devices do not allow for the thermostats of brake resistors to
be monitored via a specific terminal.
Exception: E84DHxxx7524
For special applications, e.g. centrifuges, the brake resistor must meet the following
criteria:
Brake resistor Application
Criterion With active load With passive load
Continuous braking power
[W]
w P
max
@ h
e
@ h
m
@
t
1
t
zykl
w
P
max
@ h
e
@ h
m
2
@
t
1
t
zykl
Heat quantity [Ws]
w P
max
@ h
e
@ h
m
@ t
1
w
P
max
@ h
e
@ h
m
2
@ t
1
Resistance [Ω]
R
min
v R v
U
DC
2
P
max
@ h
e
@ h
m
Active load Is able to start moving independent of the drive
(e.g. unwinder)
Passive load Is able to come to a standstill independent of the drive
(e.g. horizontal travelling drives, centrifuges, fans)
U
DC
[V] Brake chopper switching threshold from C0174
P
max
[W] Maximum occurring braking power determined by the application

e
Electrical efficiency (controller + motor)
Guide value: 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 successive braking processes (= t
1
+ dead time)
R
min
[] Minimum permissible brake resistance (see rated data of the integrated brake chopper)