Overview of Braking Resistor Selection   
 
 
If the regenerative energy generated in deceleration or 
descent in an application is too large, the main circuit voltage 
in the inverter may increase, which results in damage to the 
inverter. 
Normally, the inverter has a built-in overvoltage protection 
function, which detects an overvoltage (0 V) in the main 
circuit to prevent inverter damage. However, because it 
detects a fault to stop the motor, stable and continuous 
operation will be prevented. 
Therefore, you need to use one or more braking resistors/ 
regenerative braking units to absorb this regenerative energy 
outside the inverter. 
 
What is Regenerative Energy? 
The load connected to a motor has kinetic energy when 
rotating, and potential energy when it is subject to the gravity. 
When the motor decelerates, or when the load descends, the 
energy is fed back to an inverter. This phenomenon is known 
as  regeneration,  and  the  energy  is  called  regenerative 
energy. 
 
 
This is a simple method to select an appropriate braking resistor 
based on the percentage of the time in which regenerative energy 
is produced in a normal operation pattern. 
[r/min]
 
 
 
Time
 
 
 
 
• Usage rate [%ED] = 100 x t/T 
t: Deceleration time (regenerative time) [s] 
T: 1cycle operation time [s] 
 
For models with built-in regenerative braking circuit 
All models of the 3G3MX2-EV2 Series Inverter have built-
in regenerative braking circuit. 
Select a braking resistor based on the usage rate 
calculated from the operation pattern. 
Connect a braking resistor suitable for your inverter 
according to the braking resistor list provided in the 
inverter manual/catalog. 
 
 
 
 
 
Regenerative
 
energy
 
Kinetic energy 
Potential energy
 
 
 
When decelerating, the motor serves 
as a generator to convert the kinetic/
 
potential  energy  into  regenerative  energy. 
 
For  models  without built-in regenerative  braking  circuit 
If a braking torque or regenerative energy is extremely 
large, even the 3G3MX2-EV2 Series Inverter may 
require the Regenerative Braking Unit. 
Select an appropriate regenerative braking unit and 
braking resistor. 
 
Preventing an overvoltage (0 V) in the main circuit without use 
of braking resistors 
The following are methods to prevent the occurrence of an 
overvoltage (0 V) in the main circuit without connection of 
braking resistors. 
Since  these  methods  prolong  the  deceleration  time,  check 
that the selected method will not cause application problems. 
•  Enable the Overvoltage Suppression Function during 
  Deceleration   
The Overvoltage Suppression Function during Deceleration 
is enabled by default. 
It automatically increases the deceleration time to prevent 
the occurrence of an overvoltage in the main circuit. 
•  Set a longer deceleration time 
 
 
Increase the deceleration time to prevent the occurrence of 
an overvoltage in the main circuit. 
This decreases the amount of regenerative energy per unit 
time. 
 •  Select free-run stop   
This prevents the regenerative energy from being fed back 
to the inverter. 
Connect a regenerative braking unit and braking resistor 
suitable for your inverter according to the regenerative 
braking unit/braking resistor list provided in the inverter 
manual and catalog.