4. Select the resistor so that the following conditions are met:
•
The rated power of the resistor must be greater than or equal to P
Rmax
.
•
Resistance R must be between R
min
and R
max
given in the table for the used
drive type.
•
The resistor must be able to dissipate energy E
Rpulse
during the braking cycle T.
Equations for selecting the resistor:
For conversion, use 1 hp = 746 W.
Equation 1
When the drive supply voltage is 200 … 240 V:
When the drive supply voltage is 380 … 415 V:
When the drive supply voltage is 415 … 480 V:
Equation 2
Equation 3
R Calculated brake resistor value (ohm). Make sure that: R
min
< R < R
max
P
Rmax
Maximum power during the braking cycle (W)
P
Rave
Average power during the braking cycle (W)
E
Rpulse
Energy conducted into the resistor during a single braking pulse (J)
t
on
Braking time (one cycle) (s)
T
Braking cycle time (s)
WARNING!
Do not use a brake resistor with a resistance below the minimum value specified
for the particular drive. The drive and the internal chopper are not able to handle
the overcurrent caused by the low resistance.
174 Resistor braking
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