The crane is such an ancient machine that it has existed almost longer than written history. The earliest mention of a lifting device that mimicked the motion of today’s heavy-lifting machines came out of Mesopotamia, a crude device known as a shadouf or shaduf that consisted of a frame, a pole, and a bucket. The device appeared in areas as diverse as Egypt, Ukraine, China, and Crete. Innovations would include the addition of power produced by animals, people, and (with the advent of the Industrial Revolution) motors using various kinds of power sources such as steam, internal combustion, hydraulic pressure, and electricity.
In this guide, we will provide you with the information you need to purchase a crane motor, including details about their components, most popular configurations, common end uses, and how to size a motor for your end-use application.
Components of Crane Motors
No matter the end application of a motor, it will share certain common characteristics, the most notable being that it changes some kind of energy (e.g., steam, combustion, hydraulic) into mechanical motion. Motors that use the same kind of power will share many of the same kinds of components, and because crane motors are electric motors, they essentially work like other electric motors.
Pretty much all electric motors contain something called a stator, a stationary element containing magnets. Into this is placed a rotor. Designed to turn within the stator, a rotor also contains magnets of its own, although these are arranged so that their polarity pushes against those in the stator. This turns electromagnetic energy into mechanical energy. Other common elements include bearings (supportive structures that hold the rotor in a particular position), insulation (which protects against contaminants), and a case (which protects against physical shocks).
There are two basic kinds of electric motors. The oldest kind of electric motor is a direct current (DC) motor, which derives energy from a source where current flows continuously. DC motors may have brushes that magnetize the impermanent magnets that make the rotor turn and a commutator, which is essentially a rotary switch. Alternating current (AC) motors have power that pulses.
Both DC and AC motors are used as crane motors, although they excel at different applications.
Popular Types of Crane Motors
Though crane motors can come in a number of distinct configurations and as either DC or AC motors, they tend to have just a couple main types. In researching crane motors, you may discover references to asynchronous motors or induction motors. This is a very broad AC motor category that indicates the motor in question doesn’t turn its rotor in a manner that’s synchronized with the AC current, which fluctuates around a specific frequency. (That frequency will vary depending on the country.) In other words, it’s a way of stating that this particular kind of motor operates at a stable rate — and it represents the vast majority of AC motors, making it such a broad category that it’s scarcely useful.
Squirrel Cage Motor
The first most common kind of crane motor is an AC squirrel cage motor. This type of asynchronous motor earns its name from the unique shape of its rotor. The section that connects with the motor’s output shaft contains a pair of end caps joined to rotor bars with an outer, metal-covered section. This cage-like section gives this motor its name. These motors are relatively inexpensive, safe, efficient, and easy to maintain.
Slip Ring Motor
Another common type of crane motor is an AC slip ring motor. Also an asynchronous motor, it replaces the commutator in a DC motor with an electromechanical device called a slip ring. Often crafted of graphite or some kind of conducting metal, the ring transmits power and is used in any application with a rotating platform, making it easy to see why they’re popular with cranes.
How to Properly Size a Crane Motor
Correctly sizing any sort of motor requires a significant amount of knowledge about your current equipment and load requirements, as well as the correct calculations you need to perform. Dr. Alaa Khamis’ guide highlights the basic requirements for motor sizing include speed, load torque, and load inertia required for your specific task.
However, calculations and considerations become more complicated when considering crane motors. To start with, you should determine what kind of duty your crane will require duty types include:
- S1 – Continuous Running Duty
- S2 – Short-Time Duty
- S3 – Intermittent Periodic Duty
- S4 – Intermittent Periodic Duty with Starting
- S5 – Intermittent Periodic Duty with Electric Braking
- S6 – Continuous Operation Periodic Duty
- S7 – Continuous Operation Periodic Duty with Electric Braking
- S8 – Continuous Operation with Periodic Related Variations in Load and Speed
- S9 – Duty with Non-Periodic Load and Speed Variations
Each of these different duty types requires its own set of calculations. To learn more, read the first, second, and third parts of Ashok Parikh’s guide to crane motors at Electrical Engineering Portal.
What to Look for When Buying a Crane Motor
Every motor purchase will need to consider constants such as the size of the motor, its range of revolutions per minute (RPMs), its required voltage, and other standard elements. Understand, though, that crane motors have very unique considerations that you will have to take into account. In the previous section, we discussed the various duty types that your end-use scenario will require, which is an essential element to examine when buying a crane motor. Other aspects you should think about include:
- The motor’s ability to deliver high torque upon start up and even with low starting current
- The overload capacity of the motor, which helps ensure safer operations
- The motor’s exposure to the elements, which is often harsh
- The temperatures at which the crane will need to operate
Applications and Industries
Cranes excel at lifting heavy loads that would put human lives at risk. That makes them natural choices when it comes to:
- Construction
- Ship Building and Maintenance
- Manufacturing
- Warehousing
- Military Applications
- Cargo Shipping
- Railway Operation, Maintenance, and Construction
- Military Applications
Tips for Finding and Buying a Crane Motor
When you need to purchase a crane motor, make your selection from a trusted source. Surplus Record has decades upon decades of experience in connecting buyers and sellers with worthwhile equipment. Once you’ve determined exactly what kind of crane motor you’d like, you can easily search our listing to find out what’s available. Type “crane motor” into the search bar at the top of our website to get started.
Popular manufacturers for Crane Motors include General Electric, Westinghouse, P & H, and Reliance.
In addition to our classified listings, we have connections with multiple dealers who specialize in all kinds of different equipment. You can find dealers in your area or by name. Click on the “Dealer Search” drop down menu at the top of the page to begin your search.
