The Voltage applied to a dynamic brake resistor is dependent on the threshold set for the brake switch by the Manufacturer. This is necessary to control and limit the Current passing into the resistor.
The resistor must be in the range between the minimum resistance specified by the Manufacturer and possibly a higher value where the power adsorbed will match the energy returning from the load.
The Wattage or physical size of the resistor must be suitable to absorb the power returning from the load, not over-heat, and work with the duty cycle for the application.
Many Manufacturers product manuals show protection components installed in the brake resistor circuit. Consideration must be given to the consequences for the load in tripping the drive to protect the resistor. Opening the resistor circuit is not an option, as this will allow the DC Bus Voltage to reach its trip level, and the Inverter Drive will eventually be damaged. It might be safer to over-size the resistor to keep it cool and prevent ‘heat skinning’ increasing its resistance.
The Voltage applied will be controlled by the Current limit built into the brake control circuit, as long as the resistor value is not too high.
Most product manuals provide guidance for calculating the values for the brake resistor. The information in this article is intended as a guide, and the Manufacturers recommendations must always be followed.
Power absorbed for a given resistor is a simple calculation based on ‘Ohms Law’. That is V2/R. In general 380V DC and 750V DC can be used for the purpose of calculation for 230V and 400V Drives (for accurate figues, see the tables below and other Manufacturers manuals).
Figures for the ABB ACS180 are here: -
| DC Voltage Level (V) |
|
|
|
|
| |
208V to 240V AC Supply |
380V to 415V AC Supply |
440V to 480V AC Supply |
Automatic/Not Selected |
| Overvoltage Fault Limit: |
421 |
842 |
842 |
842 |
| Overvoltage Control Limit: |
389 |
779 |
779 |
779 |
| Internal Brake Chopper Start Limit: |
389 |
760 |
760 |
760 |
| Internal Brake Chopper Stop Limit: |
379 |
745 |
745 |
745
|
Figures for Yaskawa GA500 are here: -
| Voltage |
E1-01 Setting |
0V Detection Level |
BTR Operation Level
(rr Detection Level)
|
L2-05 (Undervoltage Detection LVl (UV1) |
L2-11 (KEB DC Bus Voltage Setpoint) |
L3-17 (DC Bus Regulation Level) |
| 200V Class: |
All Settings |
410V |
394V |
190V |
260V |
375V |
| 400V Class: |
400V/460V Setting |
820V |
788V |
350V/380V |
460V/500V |
750V |