Electromagnet
An electromagnet converts electrical current into a controllable magnetic field. It can attract suitable magnetic material or form part of an actuator. Its field also stores energy, which matters when the driving circuit switches the current off.
The fields produced by the turns of a coil combine. A ferromagnetic core can enhance the field through its magnetic response, but geometry, air gaps and core saturation limit the result. Inductance opposes changes in current: applying a voltage makes current rise over time, not jump immediately to its final resistive value. Turning off the driver requires a controlled path for the stored energy.
In plain terms
Imagine giving a crowd of tiny compass needles a common direction. Current through the coil provides the organizing field, and a ferromagnetic core responds to it. Some alignment can remain after the current is removed, so off does not always mean perfectly non-magnetic.
Why designers use it
- Control a magnetic field electrically.
- Produce attraction in a suitable holding or actuator arrangement.
- Study the relationship between coil current, magnetic material and field.
Best for
- Electromagnetic holding
- Actuator field coils
- Magnetism demonstrations
Key specifications
- Drive: Rated current or voltage and duty cycle (Check winding resistance and temperature rise.)
- Magnetic performance: Application-specific force or field (Air gap, geometry and core material matter.)
- Turn-off behavior: Stored energy and suppression (Match clamp voltage and energy handling to the driver and coil.)
When not to use it
- When the coil's thermal rating or allowed duty cycle cannot support the required energized time.
- When the design needs guaranteed zero residual magnetism but the selected core and assembly do not provide it.
Common mistakes
- Assuming an inductive coil initially draws its maximum steady-state current when a DC voltage is applied.
- Ignoring stored energy and the driver's turn-off voltage rating.
- Assuming magnetic force depends on current alone, without considering the air gap, geometry or saturation.
- Treating a freewheel diode as the only suppression option regardless of release-speed requirements.
Where you will find it
- OpenStax illustrates electromagnets used to lift ferromagnetic scrap. The required holding force still depends on the actual load and magnetic path.
- Nexperia's solenoid application note shows how a coil driver manages current and releases stored magnetic energy. Its simulation values describe examples, not universal coil ratings.
A short history
William Sturgeon exhibited his electromagnet in 1825, according to Britannica. Modern electromagnets range across very different magnetic, thermal and mechanical designs; this historical milestone does not establish a standard strength or current rating.
Good to know
- A core can retain some magnetization even after its coil current has decayed.
- A coil that produces useful force still stores magnetic energy; these are not mutually exclusive functions.