Bobbin Coil Guide: Winding & Tech Explained

The Bobbin Coil is often the unsung hero in the fields of precise fluid control and electro-hydraulics. Solenoids, proportional valves, and other devices owe their operation to these apparently simple devices.

If you are a purchasing manager sourcing components for industrial automation systems or a mechanical engineer working on hydraulic systems, it is vital you understand bobbin coils. From the basics, including definitions and operation, through construction and operation, this guide covers all aspects of bobbin coils.

A bobbin coil, or solenoid coil, is a type of electromagnetic device consisting of a copper wire wound around a rectangular or cylindrical core referred to as a “bobbin.” A magnetic field is produced when an electric current passes through the wire. A plunger or armature is actuated by this magnetic field, converting electrical energy into linear mechanical motion.

It is an electromechanical part consisting of a bobbin, which is a spool or a frame where the wire is wound. It is the most important part in devices such as relays, solenoids, proportional valves, and sensors. The bobbin makes sure the winding, insulation, and mechanical integrity are all perfect.

Important Parts of a Bobbin Coil

Core of the Bobbin (Frame)

It is usually constructed from plastic and other materials that can withstand heat.

It provides a place where the wires are wound and the structure is held together.

It is sometimes constructed in such a way that there are flanges to prevent the wires from slipping.

Winding Copper Wire

It is the part where the wires are wound and conduct electricity.

It has a single layer or more depending on the required inductance and force.

It determines the intensity of the magnetic field and the performance of the coil.

Layer of Insulation

It makes sure there are no short circuits between the layers of the wires.

It is sometimes constructed from materials such as polyester, enamel, and mica tape.

It makes sure the device is safe and efficient even at high temperatures and voltages.

Leads or Terminals

It is the part where the power supply can be connected.

It can be soldered, crimped, and plugged in.

Plunger or Core (used in proportional valves and solenoids)

It is the part where the magnetic field affects the movable part.

It is constructed from soft iron and other materials that are ferromagnetic.

The operation of a bobbin coil is based on the principles of electromagnetism:

Current Flow: An electric current passes through the copper wire.

Magnetic Field Generation: The wire is encased in a magnetic field generated by the current.

Plunger Actuation: A ferromagnetic plunger or armature is attracted by the magnetic field.

Linear Motion: The movement of the plunger is due to the magnetic force that attracts the plunger, which in turn shifts the spool inside the valve.

Bobbin coils can be grouped into different classes based on how they are encapsulated and insulated:

Standard Encapsulated Coils

Protected from dust and light moisture by being covered with plastic, usually nylon or thermoplastic.

High Temperature Coils

For high-heat applications, these coils can be used because they contain heat-resistant wire and materials, Class H and Class C.

Proportional Solenoid Coils

These coils are designed especially for proportional valves and contain unique pole tubes that ensure linear force is achieved in direct proportion to the applied current.

Rotatable Coils

These coils contain a housing that makes it easier to install the coil in confined spaces because the connector can be rotated 360 degrees.

It is important to pay attention to the following when reading the data sheet of a bobbin coil:

Voltage

12V DC, 24V DC, 110V AC, and 230V AC, which is usually internally rectified.

Power Consumption

For proportional valves, it is usually between 8 and 30 watts.

Duty Cycle

It is usually rated at 100% duty cycle.

Class of Insulation

For example, Class F 155°C and Class H 180°C.

Electrical connections

Flying leads, M12 connectors, and DIN 43650 (Form A, B, and C).

Protection Class

IP67 and IP65, which is resistant to water jets and dust.

Benefits

It is best used with proportional valves because it offers precise control and is not limited to on/off operation; it can be infinitely variable.

Reliability: Long service life because there is no mechanical wear between the coil and the armature.

Compact Design: Provides considerable force in a relatively compact package.

Standardization: The majority of coils are interchangeable between different valve manufacturers since they are all standardized to DIN specifications, e.g., DIN 43650.

Drawbacks

Heat Generation: When coils are constantly energized, heat is produced. Coil burn-out may happen if the heat is not dissipated.

Current Sensitivity: There is a direct relationship between current and magnetic force. Performance may be compromised by voltage variations.

Moisture Sensitivity: Short circuits may be caused by moisture if encapsulation integrity is breached.

Reliability, standardization, and repairability are at the top of the list for industrial clients. These are all provided by bobbin coils.

Global Interchangeability: A coil from one manufacturer may be used in a valve from another manufacturer, owing to standardized specifications like DIN 43650.

Scalability: Bobbin coils may be scaled to deliver the needed force to open a large main stage valve or a small pilot valve.

Safety: By providing maximum electrical insulation and grounding, encapsulated coils significantly reduce electrical hazards in industrial environments.

Low Maintenance: Since there are no moving parts in the coil, all that is needed is to ensure that the environment is clean and that all connections are secure.

Bobbin coils are commonly used in industrial automation systems. These include:

Standard AC Solenoid, DC solenoid , Solenoid Valve , holding electromagnet.

Hydraulic Proportional Valves: Used in turbine controls, presses, and injection molding machines.

Pneumatic Solenoid Valves: For Packaging Equipment and Automatic Assembly.

Clutch and Brake Actuation: For Heavy Machinery and Material Handling.

Medical Technology: For Ventilators and Precise Dosage Pumps.

The winding process is the most critical part that affects the performance of the bobbin coil. The optimization of the copper fill factor and the constant resistance value are the objectives.

The Process of Winding:

Bobbin Preparation: A winding machine is used to prepare the plastic bobbin, which is the former.

Wire Selection: Depending on the required resistance value and the number of turns required, copper wire with a specific gauge value is used.

Layer Winding: The wire is then wound on the bobbin. The wire is wound in such a way that it fits into the groove of the previous wire, which is known as the ‘perfect layer’ winding method and is used in the winding of the coil.

Insulation: Tape is used as the turn-to-turn insulation.

Termination: The start and end wires are terminated with the help of terminals.

Encapsulation: The wound bobbin is then over-molded with plastic.

The performance depends on the correct choice of the coil. Follow the checklist below:

Check the voltage: The voltage must match the control system voltage, which is usually 24V DC.

Check the connector type: The connector type is either DIN 43650 Form A, which is ‘large,’ or DIN 43650 Form B, which is ‘small.’

Determine the Resistance: To ensure that it meets the specifications indicated on the driver card, the resistance is measured or verified in Ohms. Higher current is generated by lower resistance.

Think About the Environment: Ensure the rating is adequate (IP67 > IP65) when the application is going to be used outside/washdown.

Temperature Rating: Select a higher insulation class (H) when the coil is near a hot manifold/engine.

Valve Series: Ensure the armature tube type of the coil is suitable for the specific valve series in use.

The coil is too hot to handle:

Cause: High ambient temperature, wrong coil type for the cycle, and excessive voltage.

Solution: Check the voltage. Ensure the valve spool is stuck and hence has a high inrush current.

The valve is not being activated:

Cause: Loose connector, broken wire, and/or burned coil.

Solution: Check the resistance. If the coil is burned out and has to be replaced, the message “Open Line” (infinite resistance) will be shown.

Unpredictable/Sporadic operation:

Cause: Broken cable and/or bad ground connection.

Solution: Ensure the ground pin is inserted and the DIN connector pins are not corroded.

AC coil-only humming noise:

Cause: Broken shaded ring and/or wrong seating of the plunger.

Solution: Clean the valve armature and/or replace the coil.

In the world of industrial control systems, the Bobbin Coil is a critical interface between mechanical motion and electronic control systems. For durable and accurate performance, it is critical to understand its bobbin winding technology, electrical characteristics, and environmental limitations.

Always prioritize the proper voltage, proper insulation, and proper protection when choosing a coil for a brand-new proportional valve project or diagnosing a malfunctioning actuator. Industrial clients promise their clients minimal downtime and maximum system performance through the use of high-quality and standardized coils..