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L100 Inverter
Motor Control
Accessories
5–5
Dynamic Braking
The purpose of dynamic braking is to improve the ability of the inverter to stop (deceler-
ate) the motor and load. This becomes necessary when an application has some or all of
the following factors:
• High load inertia compared to the available motor torque
• The application requires frequent or sudden changes in speed
• System losses are not great enough to slow the motor as needed
When the inverter slows its output frequency to decelerate the load, the motor can
temporarily become a generator. This occurs when the motor rotation develops a voltage
higher than the inverter internal (DC) bus voltage. This condition can cause the inverter
to have an over-voltage fault and enter the Trip Mode. In many applications, the over-
voltage condition serves as a warning signal that we have exceeded the deceleration
capabilities of the system. The L100 inverter can connect to an external braking unit,
which accepts the excess energy from the motor during deceleration to its internal resis-
tor(s). The power resistor serves as a generator load, developing heat to stop the motor
just as brakes on an automobile develop heat during braking. You can also add an
external resistor to the braking unit for additional braking torque.
A switching circuit and power resistor are the main components of the dynamic braking
unit, which includes a fuse and thermally activated alarm relay for safety. However, be
careful to avoid overheating its resistor. The fuse and thermal relay are safeguards for
extreme conditions, but the inverter can maintain braking usage in a safe zone. The
following table specifies the braking options for 200V class L100 inverters and the
braking torque for each option. Use BRD–E2 braking unit for 200V class inverters.
Note 1:
A = Average braking torque from 60 Hz to 3 Hz.
Note 2:
B = Average braking torque from 120 Hz to 3 Hz.
Note 3:
BRD maximum duty cycle = 10%, where T
b
/T
c
≤
0.1 sec.
Note 4:
BRD maximum continuous On time T
b
≤
10 sec.
L100 Inverter 200V Models BRD–E2 Braking Unit
Model Number HP
Braking torque
without
braking unit
Using built-in
resistor only
External resistor added
HRB1 HRB2 HRB3
A B A B A B A B
002NFE/NFU 1/4 50% 150% 120% Over-range Over-range Over-range
004/005NFE/NFU 1/2 50% 150% 120% Over-range Over-range Over-range
007NFE/NFU 1 50% 100% 80% 150% 120% Over-range Over-range
011/015NFE/NFU 2 50% 60% 60% 100% 80% 150% 120% Over-range
022NFE/NFU 3 20% 50% 50% 100% 80% 120% 100% Over-range
037LFU 5 20% 40% 40% 60% 60% 80% 80% 150% 120%
055LFU 7.5 20% 30% 30% 50% 50% 60% 60% 100% 80%
075LFU 10 20% ——40% 40% 60% 60% 80% 80%
f
time
T
b
T
c
output
Technologies Inc.
Toll Free: voice: 1-877-539-2542 fax: 1-800-539-2542 www.mgitech.com