LENZE
2
Drive selection
Technical data B-side built-on accessories
2-178
Small drives en 07/2010
Brakes
Description
Spring-applied brakes work on the closed-circuit principle,
i.e., the braking torque is generated by the spring force
when the supply is off. The brake is released electro-
magnetically by applying a DC voltage.
Spring-applied brakes should be fitted if
˘
a holding torque is required during motor standstill,
˘
the coasting time after motor disconnection must be
very short,
˘
short operating cycles (on/off cycles) are required.
Three-phase asynchronous motors are equipped with a rec-
tifier in the terminal box.
Tacho generators
DC tachogenerator
An armature with winding and commutator rotates in a
permanent magnetic field. The induced voltage is tapped at
the commutator by carbon brushes.
Features
˘
Detection of the direction of rotation when the polarity
of the tacho voltage changes
˘
Very low residual ripple of the tacho signal thanks to sui-
table dimensioning of the windings
˘
Very good linearity of the tacho signal even at very low
speeds
AC tachogenerator
A rotating permanent magnet induces a single- or multi-
phase AC voltage in the stator winding. An integrated
rectifier rectifies the AC voltage so that the output signal
is a DC voltage.
Features
˘
Simple structure (price)
˘
Simple assembly
˘
No wearing parts, therefore maintenance-free
˘
Direction of rotation not detected from polarity of the
tacho voltage, therefore not suitable for 4-Q drives
˘
Tacho voltage and speed are only proportional from
a minimum speed n
min
> 0 because of the threshold
voltage of the integrated rectifier.
Technical data
Brake
Braking torque
Brake voltage
Coil power
Rotor bore
Weight
Type
[Nm]
[DV]
[W]
[mm]
[kg]
BFK 457-03
0.5
24 or 205
9
10
0.25
BFK 457-04
1
24 or 205
12.5
7 or 10
0.3
BFK 457-05
2
24 or 205
16
10
0.4
BFK 458-06
4
24 or 205
20
10
0.8
Technical data
Design
Detection of
Voltage
Ripple
Reversing
Linearity
Minimum
Max
Thermal
Enclosure
Weight
Type
direction
per 1000 rpm
error
error
limit of
speed
limit current
[approx.
of rotation
control range
for 4-Q drives
[V]
[rpm ]
[rpm ]
[mA]
kg]
DC current
tacho
yes
20 (-10%)
< 0.3%
+
/
–
0.0%
< 0.05%
0
9000
24
IP54
0.5
Type GT7.08
Three-phase AC
current tacho
no
30 (+/– 3%)
4%
–
< 1%
60
10000
20
IP54
0.5
Type TD3