Dynamic Brake Selection for Sub-Micro & SMV Series Drives
Dynamic braking is used when an overhauling load causes regeneration from the motor to occur, especially in situations where the required deceleration time to stop the motor cannot be achieved due to High Voltage nuisance tripping. Most Lenze-AC Tech DB circuits are rated for light-duty use only. The dynamic braking (DB) control circuit is connected to and monitors the fixed DC bus line. When the DC bus reaches 114% of the maximum tolerance, it triggers the chopper circuit in the dynamic brake. The DB circuit will be active whenever the voltage rises on the DC bus. This can occur while the drive is running, while it accelerates or decelerates or even when it is stopped. Using dynamic braking allows a faster deceleration time of a high inertia load. However, fast deceleration of a high inertia load may sometimes cause regeneration and trip the drive into a High Voltage fault. To avoid this, a dynamic brake chopping circuit is switched on when the voltage levels exceed the rated tolerance and brake resistors dissipate the regenerated voltage as excess energy.
Thermal Protection from Overload for the DB Module
Lenze-AC Tech brake modules rated at 0.33 to 10 HP have resistors that are internally mounted. In these modules there is a thermistor that monitors the resistors temperature and can be connected back to the drive to trigger a drive fault.
Using a Lenze-AC Tech DB with Another Manufacturer’s Drive
Applications Support is often asked if the Lenze-AC Tech DB module can be used with a non-Lenze AC Tech drive. This is not possible. The Lenze-AC Tech sub-micro drives have specific inputs that are set to trigger the Lenze-ACTech DB modules. Other VFD manufacturers may encounter problems trying to trigger the DB chopper properly. 1 For the SMVector drives, the dynamic braking module includes a small connector that plugs onto the drive’s DC Bus Board for the B+ and B- connections. A set of mounting instructions is included.
Specifications for these Dynamic Brake Kits and diagrams are available on AC Tech Lenze manual#AN 0039A which can be viewed via PDF at our website at:
