INDUSTRY Cranes & Hoists Bonitron > Industries > Cranes & Hoists

Cranes and hoists are used extensively in industry and construction as a means to lift and place heavy loads. Many of these cranes and hoists are powered by electric motors with VFDs that allow for precision control of the load. Bonitron's drive accessories enhance VFD precision and reliability. A motor connected to a load will be either "motoring" or "overhauling". A motoring motor is converting electrical energy into mechanical energy to move the load. An overhauling motor is being driven by the load and is converting mechanical energy into electricity, acting as a generator.

Motoring vs Overhauling
  • Maximize drive system efficiency and reliability
  • Safely lower loads without tripping drives
  • Utilize braking current to power other drives
  • Backup power to protect from sags and outages

Braking/Overhauling

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

Power Sharing

Motors generating electricity while lowering a load can share power with other motors on a common DC bus.


A motor connected to a load will be either "motoring" or "overhauling". A motoring motor is converting electrical energy into mechanical energy as is the case when a load is being lifted. An overhauling motor is being driven by the load and is converting 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.

Motoring vs Overhauling

Overhead Crane

Braking/Overhauling

When a load is lowered, the motor acts as a brake, generating electrical energy which is dissipated by regen 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.

 

Dynamic Braking

The dynamic brake method typically has a lower up front cost, but heat generated by resistors can increase cost two way. 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.

 
 

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.

 

Common DC Bus

Crane and hoist applications can require the use of multiple electric motors in a system and can benefit from the use of a common DC bus. The use of a common bus allows for the reduction of wiring and components in the system as the linked drives can now share many components. It can also allow for the direct sharing of power between drives, reducing amount of power needed from the grid. This can be achieved with either a common bus power supply or with diode sharing.


Common Bus Power Supply

Using a common bus power supply reduces the amount of wiring and components in a system, resulting in a reduction of maintenance and footprint of the system. In a system with multiple motors, some motors may be regenerating while others are motoring. The common bus allows the regenerating drives to share power with the motoring drives, thus reducing the amount of power needed from the grid. If the drives are creating a net surplus of energy, a single line regen or braking unit can be installed to dissipate the excess energy.

A common bus power supply can also allow the use of single phase AC power with 3-phase motors without having to oversize the drive. The M3712 can create a common DC bus from single phase power while the M3713 uses 3-phase input power.

 

 

Common Bus Sharing Diodes
M3345CBM

If drives on the AC line are connected by a DC bus, circulating currents can be created that might cause drive faults. The sharing diodes allow a two way flow of power to and from drives enabling them to share power between their DC busses while preventing circulating currents. The two-way flow allows the drives to share power with each other and use a common braking, regen, or UPD.

 
 

Common Bus Isolation Diodes
M3460D

Unlike the sharing diodes, the isolation diodes allow only a one-way flow of power and do not allow drives to share power with each other, completely isolating the drives and preventing circulating currents. The isolation diodes allow multiple drives to be connected on the DC bus so that they can share one UPD. The M3460D allows inward flow of power so that one UPD can power all of the drives connected to the DC bus.

 

 

Emergency Power

UPD Lite

Some crane processes may not require uninterruptible power, but require enough power to shut down safely or reset the equipment to a default position during an outage. For these low speed applications the UPD can be undersized to 10-20% of the motor HP, greatly reducing the cost. This is possible because:

Power = Speed x Torque

So theoretically, if you run at one half of the regular speed with the same torque, it will use half of the regular power. Contact Bonitron to learn more about the potential of UPD Lite for your application.

 

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