The hows and whys of lifting magnets


Science Lesson #1: What’s a lifting magnet and how does it work?
A magnet is really just a string of wire wrapped around a magnetic core. This string of wire has resistance we call ohms that govern what current, also called amps, flows at a given voltage. All DC magnets obey Ohm’s law and most lifting magnets operate in a 250-volt direct current system.

At ambient (room) temperature, the magnet has the greatest lift capability since it’s resistance is at the lowest point. The time in use, or duty cycle, affects its strength.

When a magnet is energized, the internal temperature rises quickly. Because of the size and construction of the magnet case, the heat is released slowly. The internal temperature increases and so does the conductor resistance. As the magnet temperature continues to increase, current will decrease and so will the magnet’s lifting strength.

Science Lesson #2: Keeping lifting magnets in their designed operating range
Magnet operators can operate lifting magnets safely just by paying close attention to the magnet’s duty cycle. Duty cycle is the time the magnet is in use. More specifically, duty cycle is the percentage of time a magnet is to receive its rated voltage in any 10-minute period. Most magnets are designed to operate at a 50 percent or 75 percent duty cycle.

For example, in any 10-minute operating period, the magnet can run five minutes on, five minutes off for a 50 percent duty cycle. For a 75 percent duty cycle, the magnet can run for 7.5 minutes, off for 2.5 minutes.

During the off cycle, the magnet is given time to cool and – provided this rule is not broken – should allow a magnet to operate at its designed rating throughout the day.

And remember… If you see a lifting magnet, they are very powerful. Never walk or stand below a lifted magnet.

Fun science fact: Steel begins to lose its magnetic properties at roughly 1000 to 1200 degrees F. Steel becomes completely non-magnetic at 1325 degrees F.

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