KEB COMBIVERT F5-A, Applications Manual, Page: 492 / 552

Page 9.1 - 4 COMBIVERT F5-A, -E, -H © KEB, 2012-10
General design
9.1.2 Design of braking resistors
The
KEB COMBIVERT fitted with an external braking resistor or an external braking option is suitable for a
limited 4-quadrant operation. The braking energy, refeed into the DC-bus at generatoric operation, is dissipated
over the braking transistor to the braking resistor.
The braking resistor heats up during the braking process. If it is installed in a control cabinet sufficient cooling
of the control cabinet interior and sufficient distance to the KEB COMBIVERT must be observed.
Different braking resistors are available for the KEB COMBIVERT. Please refer to the next page for the corre-
sponding formula and restrictions (valid range).
1. Preset desired braking time.
2. Calculate braking time without braking resistor (t
Bmin
).
3. If the desired braking time shall be smaller than the calculated time, it is necessary to use a braking resistor.
(t
B
< t
Bmin
)
4. Calculate braking torque (M
B
). Take the load torque into account at the calculation.
5. Calculate peak braking power (P
B
). The peak braking power must always be calculated for the worst case
(n
max
to standstill).
6. Selection of braking resistor:
a) P
R
> P
B
b) P
N
is to be selected according to the cycle time(ED).
The braking resistors may be used only for the listed unit sizes. The maximum cyclic duration of a braking re-
sistor shall not be exceeded.
6 % ED = maximum braking time 8 s
25 % ED = maximum braking time 30 s
40 % ED = maximum braking time 48 s
For a longer cyclic duration time special designed braking resistors are necessary. The continuous output of the
braking transistor must be taken into consideration.
7. Check, whether the desired braking time is attained with the braking resistor (t
Bmin
).
Restriction:
Under consideration of the rating of the braking resistor and the brake power of the motor, the braking torque
may not exceed 1.5times of the rating torque of the motor (see formula).
When utilizing the maximum possible braking torque the frequency inverter must be dimensioned for the higher
current.
Braking time DEC
The braking time DEC is adjusted at the frequency inverter. If it is chosen too small the KEB COMBIVERT
switches off automatically and the error message OP or OC appears. The approximate braking time can be
determined according to following formula.