Braking Resistors - Bosch Servodyn-ASC Betriebshandbuch

5.3 Braking Resistor
Installation
Instructions
Selection of the braking
resistor
1070066022 - 101
BOSCH ASC is equipped with an external braking resistor and is
suited for restricted 4 quadrant operation. The braking energy that is
refed into the intermediate circuit during regenerative operation is
dissipated by means of the braking transistor, the control and the
braking resistor.
The braking resistor heats up during braking. If it is installed inside a
control cabinet sufficient cooling of the control cabinet interior must be
provided and sufficient distance to the BOSCH ASC must be kept.
Different braking resistors are available for BOSCH ASC. They are
selected according to their application requirements. The respective
formulas and restrictions (validitiy range) are listed on the next page.
1. Preset desired braking time.
2. Calculate braking time without braking resistor (t
3. If the desired braking time is smaller than the calculated braking
time, it will be necessary to use a braking resistor. (t
4. Calculate braking torque (M
5. Calculate peak braking power (P
for the "worst case" (n
6. Selection of the braking resistors:
a) P • P
R B
b) P is to be selected in accordance with the cyclic duration factor
N
(c.d.f).
The braking resistors may only be used for the units listed. The max.
ON period of the braking resistor may not be exceeded.
6 % c.d.f. = maximum braking time
25 % c.d.f. = maximum braking time
40 % c.d.f. = maximum braking time
Longer ON periods require special-designed braking resistors.
Take into account the continuous output of the braking transistor.
7. Check whether the desired braking time is attained with the braking
resistor (t ).
Bmin
Restriction: Considering the capacity of the braking resistor and
the braking capacity of the motor, the braking torque may not exeed
the rated torque of the motor by more than 1.5 times (see formula).
To utilize the maximum possible braking torque the frequency
inverter must be layed out for the increased current.
Servodyn - ASC
Braking Resistor
) and take the load torque into account.
B
). This must always be calculated
B
at standstill).
max
8 s
30 s
48 s
GB
).
Bmin
< t
B Bmin)
GB - 62