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Crane Hooks: Braking/Overhauling – Bonitron Crane & Hoist Solutions

By September 1, 2016July 18th, 2024No Comments

Crane Hooks is a periodic update on topics related to materials handling with a particular focus on all things crane related

A motor connected to a load will be either “motoring” or “overhauling”. A motoring motor converts electrical energy into mechanical energy as is the case when a load is being lifted. An overhauling motor is driven by the load and converts mechanical energy in to electricity, acting as a generator. When the load is being lowered the motor acting as a generator is also acting as a brake for the load.

An overhauling load is creating power that, if left alone, could potentially cause an overvoltage fault in the drive. If this happens the motor will be out of control, potentially damaging the equipment being run by the motor. The overvoltage fault can be avoided by implementing either a dynamic brake or a regenerative brake. A dynamic brake or “chopper” uses transistors and resistors to dissipate the excess energy. A regenerative brake channels the energy back onto the utility grid or into a common DC Bus where it can be used by other motors.

 

When a load is lowered, the motor acts as a brake, generating electrical energy which is dissipated by regeneration or transistor/resistor units.


Transistor & Resistor vs. Line Regeneration

Braking units prevent overvoltage faults on drives. A dynamic brake or “chopper” uses transistors, which detect overvoltage situations, together with resistors to dissipate the excess energy. A regenerative brake channels the energy back onto the utility grid where it can be used by other equipment within the facility.

A dynamic brake or "chopper" uses transistors, which detect overvoltage situations, together with resistors to dissipate the excess energy A regenerative brake channels the energy back onto the utility grid where it can be used by other equipment within the facility
Dynamic Braking

The dynamic brake method typically has a lower up front cost, but heat generated by resistors can increase cost two ways. If the resistors are indoors, added cooling capacity may be required for the room. Large resistor banks may be kept outside, far from the drive, but this results in more wiring and conduit cost. Resistors also need time to cool down after a braking cycle. Regen units are rated for continuous use and so are typically a better choice for high duty applications such as cranes and hoists where utility power is used.

A dynamic brake or "chopper" uses transistors and resistors to dissipate the excess energy. A regenerative brake channels the energy back onto the utility grid or into a common DC Bus where it can be used by other motors.
Line Regeneration

Line regen solutions have many advantages. First, because the unit does not generate high levels of heat (99% efficient), it can be integrated into the drive cabinet. Second, the unit can run continuously without the need of a cool down period. Third, the lack of heat generation allows its use in environments where there might be flammable materials such as feathers, dust, or wood. The regen also boost energy efficiency as it puts electricity back into the AC line where it can be used by other equipment, considerably reducing the demand from the utility.

Both

A regen is most effective for frequent or continuous braking up to 450A, while a transistor/resistor is more suited to higher peak loads for shorter durations. If necessary, transistor/resistor and regen units can be used together for a more efficient solution, where the regen handles continuous braking needs and the dynamic brake activates when the regens’s capacity is surpassed.

Transistor/resistor and regeneration units can be used together for a more efficient solution

Source: Bonitron Crane & Hoist Solutions | 615-244-2825