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KFU 2-/4-
216
17.4
Brake Chopper and Brake Resistance
The frequency inverters feature a brake chopper transistor. The external brake resis-
tor is connected to terminals Rb1 and Rb2. The parameter
Trigger threshold
506
defines the switch-on threshold of the brake chopper. The generator output of the
drive, which leads to the increase in the DC link voltage, is converted to heat by the
external brake resistor above the limit set via parameter
trigger threshold
506
.
Parameter
Settings
No.
Description
KFU
Min.
Max.
Fact. sett..
2- 225
385
506
Trigger
threshold
4- 425
1000.0 V
770
The parameter
Trigger threshold
506
is to be set in such a way that it is between the
maximum DC link voltage which the mains can generate and the maximum admissi-
ble DC link voltage of the frequency inverter.
max
BC
Netz
Ud
Ud
2
1,1
U
If the parameter
Trigger threshold
506
is set larger than the maximum admissible DC
link voltage, the brake chopper cannot become active, the brake chopper is switched
off.
If the parameter
Trigger threshold
506
is set to a value below the DC link voltage
generated by the mains, error message F0705 (chapter "Error Messages") is dis-
played if the start command is issued to the frequency inverter.
If the DC link voltage exceeds the maximum value of 400 V for the KFU 2- series of
devices or 800 V for the KFU 4- series of devices the error message F0700 is dis-
played (chapter "Error Messages").
The sampling time of the function is 125 µs. The brake chopper remains on for at
least 125 µs after the set trigger threshold was exceeded even if the value drops be-
low the trigger threshold within this period again.
Brake chopper
ON
OFF
125 s
µ
t
U
d
Trigger Threshold
506
t