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Relay Coil as an Electromagnet

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Recipe #34 — relay coil as an electromagnet

A relay turns the nail-electromagnet idea into a useful component. Its coil pulls a movable armature, and that armature operates one or more electrical contacts.

RELAY COIL — AN ELECTROMAGNET THAT MOVES CONTACTS +9 VSW1 K1 COIL magnetic pull NO CONTACT mechanical linkage Energize coil → armature moves → contacts change state. Remove current → spring returns them.
The relay is an electromagnet plus a mechanical switch. Current through K1 creates magnetic force, the armature moves, and the contact changes state without electrically connecting the coil circuit to the contact circuit.

Electrical isolation is one reason relays remain useful

The coil can be controlled by a low-voltage circuit while the contacts switch a different voltage or current, subject to the relay's ratings. The two circuits are coupled mechanically and magnetically rather than by a direct conductive path.

The coil is also an inductor

The winding has resistance, but it also stores energy in its magnetic field. That stored energy is why relay coils produce flyback voltage when current is interrupted—a topic revisited shortly.

Try these yourself

What physically moves the relay armature?
The energized coil magnetizes its core and pulls the armature.
Are the relay coil and contact electrically the same conductor?
They are normally electrically isolated; the coil moves the contacts mechanically.
Why can a relay coil create a voltage spike when switched off?
An inductor resists sudden changes in current and releases stored magnetic energy when the current path is interrupted.
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