Braking operation
Braking operation with brake resistor
Selection of the brake resistors
7
97
EDS84DG752 EN 5.0
7.2 Braking operation with brake resistor
To decelerate greater moments of inertia or with a longer operation in generator mode, a
brake resistor is required. It converts braking energy into heat.
The brake resistor is connected if the DC-bus voltage exceeds the switching threshold. This
prevents the controller from setting pulse inhibit through the ”Overvoltage” fault and the
drive from coasting. The brake resistor serves to control the braking process at any time.
Options with 8400 motec:
1. There is no internal brake resistor integrated in the device. Braking energy cannot be
converted into heat.
2. An internal brake resistor can optionally be attached from the corresponding
accessories ( 114). This enables the conversion of small amounts of braking
energy into heat, according to the technical data.
3. An external brake resistor can optionally be attached from the accessories ( 115).
This enables the conversion of braking energy into heat, according to the technical
data.
7.2.1 Selection of the brake resistors
The recommended Lenze brake resistors are adapted 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 brake resistor must meet the following
criteria:
Brake resistor Application
Criterion With active load With passive load
Continuous braking power
[W]
≥ P
max
⋅ η
e
⋅ η
m
⋅
t
1
t
zykl
≥
P
max
⋅ η
e
⋅ η
m
2
⋅
t
1
t
zykl
Heat quantity [Ws]
≥ P
max
⋅ η
e
⋅ η
m
⋅ t
1
≥
P
max
⋅ η
e
⋅ η
m
2
⋅ t
1
Resistance []
R
min
≤ R ≤
U
DC
2
P
max
⋅ η
e
⋅ η
m
Active load Can start to move independent of the drive
(e.g. unwinder)
Passive load Can stop independent of the drive
(e.g. horizontal travelling drives, centrifuges, fans)
V
DC
[V] Switching threshold of brake chopper (8400 motec = 783 V)
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
+deadtime)
R
min
[] Minimum permissible brake resistance (see rated data of the integrated brake chopper)
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