Instruction manual

4-68
F50 to F52
Electronic Thermal Overload Protection for Braking Resistor
(Discharging capability, Allowable average loss and Resistance)
These function codes specify the electronic thermal overload protection feature for the braking resistor.
Set the discharging capability, allowable average loss and resistance to F50, F51 and F52, respectively. These
values are determined by the inverter and braking resistor models. For the discharging capability, allowable
average loss and resistance, check with the manufacturer of the braking resistor and set the function codes
accordingly.
Depending on the thermal marginal characteristics of the braking resistor, the electronic thermal overload
protection feature may act so that the inverter issues the overheat protection alarm even if the actual
temperature rise is not large enough. If it happens, review the relationship between the performance
index of the braking resistor and settings of related function codes.
The standard models of braking resistor can output temperature detection signal for overheat. Assign an
"Enable external alarm trip" terminal command THR to any of digital input terminals [X1] to [X7], [FWD]
and [REV] and connect that terminal and its common terminal to braking resistor's terminals 2 and 1.
Calculating the discharging capability and allowable average loss of the braking resistor and configuring
the function code data
When using a braking resistor, check with the resistor manufacturer about the resistor rating and then configure
the related function codes.
The calculation procedures for the discharging capability and allowable average loss of the braking resistor differ
depending on the application of the braking load as shown below.
- Applying braking load during deceleration
During normal deceleration, the braking load decreases as the speed slows down. In the deceleration with
constant torque, the braking load decreases in proportion to the speed. Use equations (1) and (3) given below.
- Applying braking load during running at a constant speed
Different from during deceleration, in applications where the braking load is externally applied during running at a
constant speed, the braking load is constant. Use equations (2) and (4) given below.
Applying braking load during deceleration Applying braking load during running at a constant speed
 Discharging capability (F50)
The discharging capability refers to kWs allowable for a single braking cycle, which is obtained based on the
braking time and the motor rated capacity.
Data for F50
Function
0
To be applied to the braking resistor built-in type
1 to 9000
1 to 9000 (kWs)
OFF
Disable the electronic thermal overload protection
During deceleration:
Discharging capability (kWs) =
Braking time (s) x Motor rated capacity (HP) x 0.75
2
Equation (1)
During running at a constant speed:
Discharging capability (kWs) = Braking time (s)  Motor rated capacity (HP)  0.75
Equation (2)
When the F50 data is set to "0" (To be applied to the braking resistor built-in type), no specification of the
discharging capability is required.
Time
Braking load (kW)
Time
Braking load (kW)