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A solenoid is an electromagnetic actuator that converts electrical energy into controlled mechanical motion. When current flows through a coil, it creates a magnetic field that moves a ferromagnetic plunger or armature. This linear or rotary movement can then be used to operate locks, valves, switches, dispensing mechanisms, and countless other mechanical components.

Solenoids are everywhere — from smart door locks and vending machines to automotive systems, medical devices, and industrial automation. Understanding how a solenoid works is essential when selecting the right actuator for a new product or designing a custom solenoid for a specific application.

This guide covers the fundamental principles, key components, performance factors, and selection criteria — with practical insights from NEXTCORE ELECTRONIC's engineering team.

1. What Is a Solenoid?

A solenoid is typically made up of several main components:

• Copper coil — the electrical winding that generates the magnetic field
• Ferromagnetic plunger or armature — the moving part that converts magnetic force into mechanical motion
• Magnetic frame or housing — concentrates and guides the magnetic flux
• Return spring — returns the plunger to its original position when power is removed
• Guide tube — ensures smooth, friction-reduced plunger movement
• Electrical terminals — connection points for the power supply

The coil generates a magnetic field when energized. This field attracts the plunger toward the center of the magnetic circuit, where reluctance is lowest. Depending on the mechanical design, this movement can provide either pulling, pushing, or rotary motion.

2. How Does a Solenoid Work?

The basic operating process is straightforward:

1. Electrical power is supplied to the coil
2. Current flows through the copper winding
3. The coil produces a magnetic field
4. The magnetic field attracts the ferromagnetic plunger
5. The plunger moves through the required stroke
6. The mechanical movement activates another component (lock, valve, switch, etc.)
7. When power is removed, a spring or other mechanism returns the plunger to its original position

This simple energy conversion makes a solenoid a practical, compact, and reliable way to control mechanical movement electronically — without motors, gears, or complex linkages.

3. What Happens Inside the Solenoid Coil?

The coil consists of insulated copper wire wound around a core or guide tube. When voltage is applied, electrical current passes through the winding and produces a magnetic field.

The strength of the resulting electromagnetic force depends on several interrelated factors:

• Number of coil turns — more turns = stronger magnetic field (but higher resistance)
• Current — determined by voltage and coil resistance (Ohm's law)
• Magnetic circuit design — shape and material of the frame and core
• Air gap — the distance between the plunger and the magnetic pole
• Plunger geometry — shape and surface area of the moving part
• Magnetic material — permeability of the steel used in the frame and plunger
• Stroke position — force varies depending on plunger position within the stroke

4. How Does the Plunger Move?

The plunger is manufactured from a ferromagnetic material (typically low-carbon steel with specific magnetic properties). When the coil is energized, the magnetic field attracts the plunger toward the center of the magnetic circuit.

The resulting movement can be configured in different ways:

The correct configuration depends on your application, available installation space, and required mechanical interface.

5. What Determines Solenoid Force?

Solenoid force is not constant throughout the stroke. In conventional designs, magnetic force is significantly affected by the air gap between the plunger and the magnetic components.

As the plunger approaches the magnetic pole, the magnetic circuit becomes more efficient and the available force generally increases. This is why engineers need to specify both initial-force and end-force requirements — not just "a strong solenoid."

6. What Is the Role of the Return Spring?

A return spring is commonly used to move the plunger back to its initial position when electrical power is removed.

The spring must be carefully matched to the electromagnetic force:

• If the spring force is too high, the solenoid may not generate enough initial force to start the movement.
• If the spring force is too low, the plunger may not return reliably (especially at high speeds or under vibration).

For some applications, gravity, external mechanical loads, or another actuator may provide the return force instead of a spring. However, a spring-return design is the most common and offers fail-safe operation — the plunger returns even during a power failure.

7. AC Solenoid vs DC Solenoid

Solenoids can be designed for either AC or DC power. The choice depends on the available power supply, control system, and application requirements.

Selection between AC and DC depends on: available power supply, required response time, noise requirements, duty cycle, control system, and application environment.

8. What Is Solenoid Duty Cycle?

Duty cycle describes how long a solenoid is energized compared with its total operating cycle.

Example: If a solenoid operates for 2 seconds and remains off for 8 seconds — Duty cycle = 20%.

Duty cycle is critical because electrical power is converted into heat inside the coil. A solenoid designed for intermittent operation (e.g., 10–20% duty cycle) should not be used for continuous energization (100% duty cycle) — it will overheat and fail.

When selecting a solenoid, engineers should specify:

• ON time (seconds or milliseconds)
• OFF time
• Operating frequency (cycles per hour / per day)
• Continuous or intermittent operation

These parameters help determine the appropriate coil design, wire gauge, and thermal performance.

9. Why Do Solenoids Get Hot?

Heat is primarily generated by electrical resistance in the coil (I²R losses). Longer energization periods generally produce more heat.

Excessive temperature can lead to:

• Reduced coil lifespan
• Insulation degradation
• Increased electrical resistance (positive temperature coefficient)
• Reduced reliability
• Coil burnout

For applications with strict temperature requirements, engineers can consider:

• Lower-power coil designs — optimized magnetic circuit for higher force per watt
• PWM control — reduces holding current after initial pull-in
• Improved magnetic efficiency — reducing the current needed for a given force
• Appropriate duty cycle — matching the coil to the actual operating pattern
• Better thermal dissipation — larger housing, heat sinks, or forced cooling
• Higher insulation class — Class F (155°C) or Class H (180°C)

10. What Are the Main Types of Solenoids?

Different applications require different solenoid configurations. Here are the most common types:

11. How to Select the Right Solenoid

When selecting a solenoid for an OEM product, engineers should consider at least the following parameters:

Providing these specifications to a solenoid manufacturer can significantly shorten the development process and ensure the final product meets your expectations.

12. When Should You Use a Custom Solenoid?

A standard off-the-shelf solenoid may not be suitable when your product has specific requirements for:

• Installation dimensions (length, diameter, mounting pattern)
• Stroke (standard parts may not offer the exact travel you need)
• Force (higher or lower than catalog options)
• Voltage (not standard 12V, 24V, or 120V)
• Power consumption (must be minimized for battery operation)
• Noise (silent operation required)
• Temperature (high- or low-temperature environments)
• Response time (faster or slower than standard)
• Service life (more than 1 million cycles)

13. What Information Should You Provide to a Solenoid Manufacturer?

If you are developing a new product and need a custom solenoid, providing the following information is helpful:

1. Application — what does the solenoid need to do?
2. Required voltage — AC or DC, nominal voltage and tolerance
3. Required stroke — total travel distance in mm
4. Required force or load — at initial stroke and end stroke (in N or kg)
5. Operating frequency — cycles per hour / per day
6. Duty cycle — ON time vs. total cycle time
7. Available installation space — maximum length, width, height
8. Working temperature — ambient and maximum internal temperature
9. Expected service life — number of cycles or years
10. Sample, drawing, or existing actuator — if available

If you do not have a complete solenoid design, an experienced manufacturer can often help determine the appropriate configuration based on your application requirements.

Why NEXTCORE for Custom Solenoid Solutions?

For OEM equipment manufacturers, choosing the right solenoid is more than selecting a voltage and stroke. The actuator needs to work reliably within the complete mechanical, electrical, and environmental conditions of the final product.

NEXTCORE ELECTRONIC provides custom solenoid solutions for OEM applications, including tubular solenoids, push-pull solenoids, rotary solenoids, latching solenoids, and other electromagnetic actuators.

• ✔ Engineering expertise — FEA magnetic simulation, thermal analysis, and material selection
• ✔ Fast prototyping — custom samples in 2–3 weeks
• ✔ ISO9001 & Sedex 4P — certified quality and ethical manufacturing
• ✔ Competitive pricing — direct factory with no middleman
• ✔ Full support — from concept through mass production

If you have a drawing, sample, existing solenoid, or simply a project requirement, our engineering team can evaluate the application and develop a suitable solenoid solution.

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FAQ — Solenoid Basics