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Digistart D3: User Guide
Issue: G
10.5 DC Brake with External Zero Speed Sensor
For loads which may vary between braking cycles, there are benefits in using an external zero-speed sensor to
interface with the Digistart D3 for brake shut-off. This control method ensures that the Digistart D3 braking will always
shut off when the motor has reached a standstill, thus avoiding unnecessary motor heating.
The following schematic diagram shows how you can use a zero-speed sensor with the Digistart D3 to turn the brake
function off at motor standstill. The zero-speed sensor (A2) is often referred to as an under-speed detector. Its
internal contact is open at zero-speed and closed at any speed above zero-speed. Once the motor has reached a
standstill, DI4, +24V will open and the starter will be disabled. When the next start command is given (ie next
application of K10), DI4, +24V closes and the Digistart D3 is enabled.
The Digistart D3 must be operated in remote mode and Pr 3A
Input A Function
must be set to 'Starter Disable'.
CAUTION
If the brake torque is set too high, the motor will stop before the end of the brake time and the motor will
suffer unnecessary heating which could result in damage. Careful configuration is required to ensure safe
operation of the starter and motor.
A high brake torque setting can result in peak currents up to motor DOL being drawn while the motor is
stopping. Ensure protection fuses installed in the motor branch circuit are selected appropriately.
CAUTION
Brake operation causes the motor to heat faster than the rate calculated by the motor thermal model. If
you are using brake, install a motor thermistor or allow sufficient restart delay (Pr 6G).
