Rockwell Automation DC3N DC Drive User Guide, 1/4-2HP-115/230 VAC User Manual

Page 31

Operation

Dynamic braking

Dynamic braking may be used to rapidly stop a motor as shown in Figure 13 on
page 24. For the RUN/BRAKE switch, use a two-pole, two-position switch rated
for at least 250 VDC, 20 amps. For the dynamic brake resistor, use a 40-watt
minimum, high power, wirewound resistor.

Dynamic brake resistor value

Sizing the dynamic brake resistor depends on load inertia, motor voltage, and
braking time. Use a lower-value, higher-wattage dynamic brake resistor to stop a
motor more rapidly.

IMPORTANT

: For motors rated 1/17 horsepower and lower, a brake resistor is not

necessary since the armature resistance is high enough to stop the motor without
demagnetization. Replace the dynamic brake with 12 gauge wire.

Table 2. Recommended Dynamic Brake Resistor Sizes

Motor

Minimum

Armature

Dynamic Brake

Current Rating

Resistor Value

Resistor Wattage

Less than 2 ADC

1 ohm

2–3 ADC

5 ohm

3–5 ADC

10 ohm

10W

5–10 ADC

20 ohm

20W

10–17 ADC

40 ohm

50W

ATTENTION:

Wait for the motor to completely stop before switching it back

to RUN. This will prevent high armature currents from damaging the motor or
drive.

ATTENTION:

Armature output can drift full ON with the switch in the

BRAKE position and will be driven full ON if the minimum speed option is
selected with the inhibit circuit. Failure to observe this precaution could result
in severe bodily injury or loss of life.