# Electronic Overcurrent Protection (pr. 9) - Mitsubishi Electric FR-A500 Instruction Manual

Transistorized inverter.

Note: 1.
In S-shaped acceleration/deceleration pattern A (refer to page 84), the set time is a period
required to reach the base frequency set in Pr. 3.
• Acceleration/deceleration time calculation expression when the set frequency is the base
frequency or higher
4
×
t =
9
(Pr.3)
• Guideline for acceleration/deceleration time at the base frequency of 60Hz (0Hz to set frequency)
Frequency setting (Hz)
Acceleration/
decelerationtime (s)
2. If the Pr. 20 setting is changed, the settings of calibration functions Pr. 903 and Pr. 905
(frequency setting signal gains) remain unchanged. To adjust the gains, adjust calibration
functions Pr. 903 and Pr. 905.
3. When the setting of Pr. 7, Pr. 8, Pr. 44, Pr. 45, Pr. 110 or Pr. 111 is "0", the acceleration/
deceleration time is 0.04s. At this time, set 120Hz or less in Pr. 20.
4. If the shortest acceleration/deceleration time is set, the actual motor acceleration/deceleration time
cannot be made shorter than the shortest acceleration/deceleration time determined by the mechanical
system's J (moment of inertia) and motor torque.
5. Changing the Pr. 21 setting changes the setting values of acceleration/deceleration time (Pr. 7, Pr. 8, Pr.
16, Pr. 44, Pr. 45, Pr. 110, Pr. 111, Pr. 264, Pr. 265). (The Pr. 611 setting is not changed.)
<Example>
When Pr. 21 = "0", setting "5.0"s in Pr. 7 and "1" in Pr. 21 changes the Pr. 7 setting to "0.5"s
4.2.6

## Electronic overcurrent protection (Pr. 9)

Pr. 9 "electronic thermal O/L relay"
Set the current of the electronic overcurrent protection to protect the motor from overheat. This feature
provides the optimum protective characteristics, including reduced motor cooling capability, at low speed.
Parameter Number
9
Rated output current*
*0.4K and 0.75K are set to 85% of the rated inverter current.
<Setting>
• Set the rated current [A] of the motor.
(Normally set the rated current value at 50Hz if the motor has both 50Hz and 60Hz rated current.)
• Setting of "0" makes the electronic overcurrent protection (motor protective function) invalid. (The inverter's
output transistor protective function is valid.)
• When using the Mitsubishi constant torque motor, first set any of "1" or "13 to 18" in Pr.71. (This provides a
100% continuous torque characteristic in the low-speed range.) Then, set the rated motor current in Pr. 9.
Note: 1. When two or more motors are connected to the inverter, they cannot be protected by the
electronic overcurrent protection. Install an external thermal relay to each motor.
2. When a difference between the inverter and motor capacities is large and the setting is small, the
protective characteristics of the electronic overcurrent protection will be deteriorated. In this case,
use an external thermal relay.
3. A special motor cannot be protected by the electronic overcurrent protection. Use an external
thermal relay.
T
5
2
× f
+
T
2
9
T: Acceleration/deceleration time setting(s)
f: Set frequency (Hz)
5
15
Factory Setting
Setting Range
60
120
5
12
15
35
Pr. 71 "applied motor"
0 to 500A
76
PARAMETERS
200
27
82
Related parameters
400
102
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