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Magnetic Potential
Generally, a continuously powered electromagnet will be weaker than a permanent magnet of the same size. However, an intermittently powered electromagnet that is allowed to cool down, or is forcibly cooled by a heat sink or other cooling method, can be considerably stronger than a permanent magnet.
Heat
The key difference between electromagnets and permanent magnets is that electromagnets create heat during operation. This byproduct needs to be managed for safe, consistent and uninterrupted operation, especially of in larger electromagnets requiring water cooling. Permanent magnets are often used in tandem with electromagnets, boosting the efficiency and usefulness of both types.
Life of Magnet
The creation of heat during the electromagnetic process of operation slowly shortens the life of the ferromagnetic material being charged . This places limits on how much it can be charged and for how long. Outside of natural processes of weathering, on the other hand, a permanent magnet can theoretically last for millions of years.
Various Uses
Many types of engines, from wind turbine generators to the power plants inside of electric cars, use a combination of electromagnets and permanent magnets to harness excess energy output. In microelectronics, this combination is especially useful, making hard drives and small motors possible. Some small appliances and gadgets, like magnetic jewelry and magnetized screwdrivers, use the passive attraction of permanent magnets for useful purposes.