DE-STA-CO F5-B AC Inverter Drive - Manual (Page 24)

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Different braking resistors are available from KEB. They are selected according to their
application requirements. The selection formulas and technical data of the resistors are
listed on the following pages. In most cases the suggested braking resistor is sufficant.
This can be verified using the procedure below.
*Braking resistors aren’t required on 1/3 to 1 HP applications
1. Establish desired braking time.
2. Calculate braking time without braking resistor (t
Bmin
).
3. If the desired braking time is shorter than the calculated braking time, it will be nec-
essary to use a braking resistor. (t
B
< t
Bmin
)
4. Calculate braking torque (T
B
) taking the load torque (T
L
) into
account. T
L
is a positive value for friction and windage and negative for overhauling loads.
5. Calculate peak braking power (P
B
). This must always be calculated for the "worst
case" (n
max
to standstill).
6. Selection of the braking resistors:
a)
The resistor should be selected so that P
R
> P
B.
b) P
N
is to be selected according to the duty cycle factor (d.c.f.).
The braking resistors may only be used for the specified value. The maximum
ON period of the braking resistor may not be exceeded.
6 % d.c.f. = maximum braking time 8 s
25 % d.c.f. = maximum braking time 30 s
40 % d.c.f. = maximum braking time 48 s
Longer ON periods require specially-designed braking resistors. Take into ac
count the current through the braking transistor.
7. Check whether the desired braking time is attained with the selected braking resistor
(t
Bmin
).
Braking time
3.4.4 Selection
Note: Consider the capacity of the braking resistor and motor. The braking torque may
not exceed the rated torque of the motor by more than 1.5 times. To realize maximum
possible braking torque, the frequency inverter must be sized for the increased motor
current.
The braking time is adjusted in the frequency inverter through the deceleration param-
eters. If the selected deceleration time is too short, either the peak inverter current level
or the maximum DC bus voltage will be exceeded. The error message
E.OC or E.OP will
result. The following formulas can be used to determine an allowable braking time.
Installation and Connection