Danfoss VLT AutomationDrive FC 300, Design Manual, Page: 59 / 296

To control the electro-magnetic brake, use the following steps:
1. Use any relay output or digital output (terminal 27 or 29). If necessary, use a contactor.
2. Ensure that the output is switched off as long as the adjustable frequency drive is unable to drive the motor.
Examples include the load being too heavy or the motor not being mounted.
3. Before connecting the mechanical brake, select [32] Mechanical brake control in parameter group 5-4* Relays (or in
group 5-3* Digital Outputs ).
4. The brake is released when the motor current exceeds the preset value in 2-20 Release Brake Current .
5. The brake is engaged when the output frequency is less than the frequency set in 2-21 Activate Brake Speed [RPM]
or 2-22 Activate Brake Speed [Hz] and only if the adjustable frequency drive carries out a stop command.
NOTICE!
For vertical lifting or hoisting applications it is strongly recommended to ensure that the load can be stopped in case of
an emergency or a malfunction. If the adjustable frequency drive is in alarm mode or in an overvoltage situation, the
mechanical brake cuts in.
For hoisting applications, make sure that the torque limits in 4-16 Torque Limit Motor Mode and 4-17 Torque Limit Generator
Mode are set lower than the current limit in 4-18 Current Limit . It is also recommended to set 14-25 Trip Delay at Torque Limit
to “0”, 14-26 Trip Delay at Inverter Fault to “0” and 14-10 Line Failure to [3] Coasting .
3.9.1 Hoist Mechanical Brake
The VLT
®
AutomationDrive features a mechanical brake control specifically designed for hoisting applications. The hoist
mechanical brake is activated by 1-72 Start Function [6]. The main difference compared to the regular mechanical brake
control is that the hoist mechanical brake function has direct control over the brake relay. Instead of setting a current to
release the brake, the torque applied against the closed brake before release is defined. Because the torque is defined
directly, the setup is more straightforward for hoisting applications.
Use
2-28 Gain Boost Factor , to obtain quicker control when releasing the brake. The hoist mechanical brake strategy is based
on the following three-step sequence, where motor control and brake release are synchronized to obtain the smoothest
possible brake release.
1. Pre-magnetize the motor
To ensure that there is a hold on the motor and to verify that it is mounted correctly, the motor is first pre-
magnetized.
2. Apply torque against the closed brake
When the load is held by the mechanical brake, its size cannot be determined, only its direction. The moment the
brake opens, the load must be taken over by the motor. To facilitate the takeover, a user-defined torque that is set
in
2-26 Torque Ref is applied in the hoisting direction. This is used to initialize the speed controller that finally takes
over the load. To reduce wear on the gearbox due to backlash, the torque is ramped up.
3. Release brake
When the torque reaches the value set in 2-26 Torque Ref , the brake is released. The value set in 2-25 Brake Release
Time determines the delay before the load is released. To react as quickly as possible on the load-step that follows
upon brake release, the speed-PID control can be boosted by increasing the proportional gain.
Product Introduction Design Guide
MG34S222 Danfoss A/S © Rev. 2014-02-10 All rights reserved. 57
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