Ohm’s law — How a lifting magnet work


Industrial Lifting Magnets are very simple machines. They are nothing more than a string of wire wrapped around a magnetic core. This string of wire has resistance (ohms) that govern what current (amps) flows at a given voltage (volts). All DC magnets obey Ohm’s law.

A magnet at room temperature, or ambient temperature, has the greatest lift capability since its resistance is at its lowest point. The time in use (duty cycle), affects its strength. More specifically, the duty cycle is the percentage of time a magnet is to receive its rated voltage in any 10-minute period.

To operate a magnet, it’s important to pay strict attention to the magnet’s duty cycle. Most magnets are designed to work 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.

When a magnet is used, or energized, it warms up. The internal temperature rises quickly, and 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. Therefore, as the temperature continues to increase, current will decrease, and so will the magnet’s lifting strength.

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.

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