What Is a Solenoid?
A solenoid is an electromagnet that creates a magnetic field when current passes through it and moves an iron piston (core) linearly. It produces not rotation but a push/pull motion.
How Does It Work?
The magnetic field created when current is given to a coil pulls the movable core inside the coil. When the current is cut, a spring returns the core to its former position.
Difference From a Motor
A motor rotates continuously; a solenoid makes only a short, linear move (on/off). So it's used in "two-position" mechanical jobs like valves, locks and latches.
| Property | Solenoid |
|---|---|
| Motion | Linear (push/pull) |
| Position | Usually two (on/off) |
| Drive | Transistor + flyback |
Where Is It Used?
Solenoid valves (water/air/fuel), door locks, machine latches, washing-machine water intake and relay mechanisms (a relay contains a solenoid too).
Driving and Protection
Since a solenoid is a coil, it isn't driven directly by an MCU; a transistor is used. A flyback diode in reverse-parallel with the coil is essential for the reverse voltage it produces when switched off.
Pull-in and Holding Current
A solenoid needs a high pull-in current to pull the piston; but once the piston seats, far less current is enough to hold it. Some driver circuits reduce the current after the initial pulse (peak-and-hold) to lower heating and energy consumption.
Common Mistakes
- No flyback: the reverse voltage burns the driver.
- Continuous energy: keeping it energized for a long time overheats the solenoid.
- Insufficient power: low current doesn't pull the core fully (half position).
Frequently Asked Questions
Is a solenoid a motor?+
Why does it heat up?+
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