Resistor braking
138
2. Select a suitable drive and brake resistor combination for the application
according to the rating table on page 141. Take also account of other factors in
the drive selection. The braking power must be greater than or equal to the
maximum power generated by the motor during braking:
where
3. Check the resistor selection. The energy generated by the motor during a 400-
second period must not exceed the resistor heat dissipation capacity E
R
.
Note: If the E
R
value is not sufficient, it is possible to use a four-resistor assembly
in which two standard resistors are connected in parallel, two in series. The E
R
value of the four-resistor assembly is four times the value specified for the
standard resistor.
A resistor other than the standard resistor can be used provided that:
• its resistance is not lower than the resistance of the standard resistor
WARNING! Never use a brake resistor with a resistance below the value specified
for the particular drive / brake chopper / resistor combination. The drive and the
chopper are not able to handle the overcurrent caused by the low resistance.
• the resistance does not restrict the braking capacity needed ie,
where
• the heat dissipation capacity (E
R
) is sufficient for the application, see step 3
above.
Placing the brake resistors
All resistors must be installed outside the drive module in a place where they will
cool and the maximum allowed cable length (10 m [33 ft]) is not exceeded.
Arrange the cooling of the resistor in a way that:
• no danger of overheating is caused to the resistor or nearby materials
P
br
denotes P
br5
, P
br10
, P
br30
, P
br60
, or P
brcont
depending on the duty cycle.
P
max
Maximum power generated by the motor during braking
U
DC
Voltage over the resistor during braking eg,
1.35 · 1.2 · 415 V DC when supply voltage is 380 to 415 VAC
1.35 · 1.2 · 500 V DC when supply voltage is 440 to 500 VAC
R Resistor resistance (ohm)
P
br
> P
max
P
max
<
U
DC
R
2
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