I. Introduction
Construction hoists are usually used in conjunction with tower cranes on construction sites. A typical construction hoist has a lifting capacity of 1-3 tons and operates at speeds ranging from 1 to 60 meters per minute. There are many types of construction hoists; classified by operation mode, they include: counterweight type and non-counterweight type; classified by control method, they include manual control and automatic control. In practical applications, frequency conversion devices and PLC control modules can also be added, along with floor calling systems and leveling systems.
II. Main Components of Construction Hoists
Guide rail frame, cage, drive system, wall attachment frame, base frame guardrails, electrical system, safety protection devices, cable power supply device, etc.
III. Problems with Conventional Construction Hoists
1. Control System
The control system is the key part of a construction hoist and determines the overall performance. Traditional hoists use contactor-based control methods, which result in single-speed operation, large start-up and braking impact, significant damage to structural and mechanical components, and frequent failure of electrical parts. The operating speed is generally low, around 34–38 m/min, which affects both construction efficiency and enterprise profitability. Simply increasing the speed would cause excessive acceleration and greater impact on the structure and mechanisms, accelerating gear and brake disc wear, thereby reducing operational reliability.
2. Start-up and Braking Systems
Conventional hoists typically use direct-on-line (DOL) starting, which results in high inrush current that severely damages motors and electrical components. At the same time, materials inside the hoist may fall during start-up, posing a serious safety hazard.
Braking in conventional hoists is achieved through mechanical friction brakes. When the hoist stops suddenly from high speed, inertia causes impact on the structure and mechanisms, damaging them and causing materials inside the hoist to fall, which poses a safety risk.
3. Leveling System
Conventional hoists do not have a creeping phase when decelerating for leveling. They decelerate directly from operating speed to zero speed. The leveling process is manually controlled by the operator based on visual judgment, resulting in low efficiency. Several attempts are often required to achieve accurate leveling, which reduces efficiency and increases fatigue on the driving and control systems, shortening their lifespan. It also makes material handling difficult, wasting time and affecting work efficiency.
IV. Features of the Frequency Conversion Control System
Using frequency conversion speed control technology allows stepless speed regulation during start-up and braking. Experiments show that a 2-second start/stop time can reduce acceleration to 0.5 m/s². The starting current is small—only 1.4 times the rated operating current. These features address the above problems effectively. Additionally, the frequency conversion control system has strong anti-interference capabilities and can operate reliably in harsh construction environments. Applying modern AC frequency conversion speed control technology to upgrade the hoist's electric drive system enables smooth operation, improves running efficiency, enhances overload performance, eliminates start-stop impact, reduces electrical maintenance, lowers energy consumption, and improves power factor, achieving excellent results. It also includes overcurrent, overvoltage, undervoltage, input phase loss protection, as well as protections against inverter overheating, overload, overspeed, brake unit overheating, I/O faults, and motor faults. Stepless speed control effectively solves transmission impact issues, extending the life of gears, rollers, bearings, and racks. Due to the current-limiting function of the frequency converter, the inrush current during motor startup is reduced, alleviating the impact on the power grid and improving the interaction between electrical devices. This significantly increases cable current-carrying capacity. Power cables need not be larger and can even be smaller than those used in conventional-speed hoists, saving costs and facilitating cable management.
A high-performance leveling control system. In traditional hoists, leveling is manually controlled by the operator based on visual estimation, resulting in low efficiency and requiring multiple up/down adjustments to achieve accurate stopping. This reduces efficiency and increases fatigue on the drive and control systems, shortening their lifespan. Using frequency conversion for leveling simplifies the entire system and completely replaces relay-based systems with high failure rates.
V. Advantages of CMC Electrical’s Construction Hoist Dedicated Inverters:
1. High Starting Torque
High torque at low frequencies, 180% of rated torque at 0.5 Hz;
2. Multiple Protection Mechanisms
Brake short circuit protection, brake resistor short circuit protection, motor overheat and overload protection, etc.
3. Simple and Easy to Use
No parameter tuning required; ready to use upon power-on;
4. Intelligent Integration
Integrated overload protection, voice announcement, and status display panel;
5. Safety
The frequency conversion speed control system provides under-voltage, overvoltage, over-torque, over-current protection, ensuring the reliability and safety of the entire electrical control system. Since the system uses zero-speed braking, there is no relative friction on the brake, theoretically giving it an infinite service life, and practically extending its life by at least tenfold.
VI. Conclusion:
Based on extensive real-world applications of CMC’s BM hoisting series dedicated inverters across China, these inverters provide smooth speed adjustment and precise control, effectively ensuring safe and stable operation of construction hoists. The system’s production efficiency has been greatly improved, while operation is convenient and maintenance is easy, helping customers reduce operating costs and improve work efficiency. These inverters are highly recommended for widespread adoption and use.
