Flipper Coil – Structure, Function, and Interesting Facts

The pinball coil—commonly referred to as a “coil” in English-speaking countries—is one of the most important electromechanical components of a pinball machine. Virtually every movement within a pinball machine is generated directly or indirectly by a coil. Whether it’s moving the flipper fingers, triggering a pop bumper, ejecting a ball, or resetting a drop target—in most cases, a pinball coil is responsible for this movement.

Although coils often appear unremarkable on the outside, they play a central role inside a pinball machine. It is only through their interaction with pistons, sleeves, stops, and other mechanical components that the precise movements which make the game so dynamic are created.

Since coils are activated thousands of times during every game, they are also among the most heavily used components in a pinball machine. A basic understanding of how they work therefore helps not only with repairs, but also with maintenance and troubleshooting.

What is a pinball coil?

A pinball coil is an electromagnetic actuator. It converts electrical energy into mechanical motion within a few milliseconds. Inside the coil is a copper winding wrapped around a coil form. As soon as current flows through this winding, a magnetic field is generated.

This magnetic field pulls a movable metal piston—often called a plunger—into the interior of the coil. The piston’s movement is then transmitted to the actual game function via various mechanical components.

Depending on its application, the piston may, for example, move a flipper finger, eject the ball from the ball tray, activate a pop bumper, or trigger other mechanical functions on the playfield. As soon as the current stops flowing, the magnetic field disappears and a return spring brings the piston back to its starting position. This allows the solenoid to be immediately reactivated for the next game action.

Why does a pinball machine have so many solenoids?

Many beginners assume that solenoids are located only under the flipper fingers. In fact, modern pinball machines often feature several dozen solenoids working together. They perform a wide variety of tasks on the playfield and ensure that nearly every mechanical movement can be executed automatically.

Typical applications include, among others:

- Flipper fingers

- Pop bumpers

- Slingshots

- Ball trough

- Scoops

- Diverter

- Drop targets

The more complex a pinball machine’s design, the more solenoids are typically used.

How is a pinball solenoid constructed?

Although solenoids vary depending on the manufacturer and application, their design is almost always based on the same principle. A complete solenoid assembly typically consists of several components that work together to ensure reliable movement.

The actual coil consists of an insulated coil body with a copper winding. Inside, the plunger moves; when activated, it is attracted by the magnetic field. To ensure this movement occurs with as little friction as possible, the plunger slides through a coil sleeve, which also reduces wear.

Detailed Structure of a Pinball Coil

The following illustration shows the most important components of a classic pinball coil. Only the interaction of all these components ensures that movements in the pinball machine can be executed precisely, powerfully, and reliably.

At the end of its travel, the plunger strikes the coil stop, which limits the stroke and enables force transmission. Depending on the application, additional components such as return springs, mounts, linkages, or lever mechanisms are included to transmit the motion to the respective game function. It is only through the interaction of all these components that a pinball coil operates reliably, powerfully, and consistently over many thousands of switching cycles.

Why do pinball coils come in different sizes?

Not every movement in a pinball machine requires the same amount of force. While a pop bumper only needs to deflect the pinball briefly, pinball fingers require significantly more energy to strike the ball in a controlled manner across the playfield. For this reason, pinball coils differ in their size, winding, and electrical design. Some coils generate a particularly powerful, short stroke, while others are designed for longer movements or a continuous holding current.

This allows each game function to be precisely tailored to its specific task. The coil used is therefore always part of a pinball machine’s overall design and should not be replaced with another model without careful consideration.

The Two Windings of a Pinball Coil—Why Some Coils Perform Two Tasks Simultaneously

Anyone who takes a closer look at a pinball coil will sooner or later come across terms like “power winding,” “hold winding,” or “dual-wound coil.” Coils with two separate windings are frequently used, especially in the main flippers of many pinball machines. The reason for this lies in the varying force requirements during a pinball movement.

As soon as the player presses the flipper button, the flipper finger must generate maximum force within a very short time to strike the ball precisely across the playfield. The so-called “power winding” is used for this initial, powerful impulse. It generates a particularly strong magnetic field and pulls the piston into the coil at high speed.

As soon as the plunger reaches its end stop, this high-power winding is deactivated. If it remained active continuously, the coil would heat up significantly within a short time and could be damaged.

From this point on, the second winding—the so-called “Hold Winding”—takes over. It requires significantly less current and simply holds the piston in its end position as long as the player keeps the flipper button pressed. This keeps the flipper finger raised without placing unnecessary strain on the coil. This interaction enables powerful flipper movements while minimizing heat generation and protecting the entire mechanism.

The EOS Switch—An Important Component of Many Pinball Coils

Closely connected to the pinball coil is the so-called EOS switch. The abbreviation stands for “End of Stroke,” meaning the end of the stroke. In many classic pinball machines, this switch is located directly on the flipper mechanism. As soon as the piston reaches the end of its stroke, the EOS switch is activated and interrupts the current flow to the power winding. At the same time, only the hold winding remains active.

Without this switching mechanism, the main winding would operate continuously at full power. This would result in the coil overheating, unnecessary energy consumption, and, in the worst case, damaged windings or scorched components. Modern pinball machines often handle this switching electronically via the control boards. However, the basic principle remains the same: maximum power when activating, significantly lower power when holding.

Typical Wear Parts of a Pinball Coil

The coil itself has no moving parts and often lasts for many years under normal operation. Nevertheless, the entire coil assembly is subject to natural wear and tear. The coil sleeve, in particular, is one of the classic wear parts. Due to the constant movement of the piston, it wears down or becomes contaminated over time. This increases friction, which in turn can lead to a noticeable loss of power.

The piston itself also frequently shows significant signs of wear after many thousands of switching cycles. Worn surfaces or burrs can impair smooth operation and should be checked regularly. The coil stop should not be overlooked. It absorbs some of the kinetic energy with every stroke and also wears out over time. A worn stop alters the mechanism’s stroke and can directly affect the feel of the game.

For this reason, several components are often replaced at the same time during a pinball mechanism overhaul. A new sleeve alone often significantly improves function, but in many cases it’s worth replacing all the wear parts within the assembly.

How can you tell if a pinball coil is defective?

An actual burned-out coil is much less common than many pinball owners assume. Often, the cause of weak or faulty operation lies in worn components around the coil or in problems within the control system. Nevertheless, there are some typical signs that may indicate a damaged or overloaded coil.

These include, for example, a significantly reduced impact force of the flipper fingers, unusually high heat generation, or a noticeable smell of burnt paint. Visible discoloration of the winding or damaged connection wires should also be taken seriously. Likewise, worn sleeves, stiff pistons, or defective EOS switches can cause similar symptoms. For this reason, the entire assembly should always be inspected before replacing a coil.

Maintenance significantly extends service life

Pinball coils themselves require very little maintenance. The situation is different for the surrounding components. Regular maintenance of the entire mechanical system plays a key role in ensuring that the coil can operate at full capacity over the long term. This includes, in particular, inspecting sleeves, pistons, stops, and return springs. Dirt and debris should be removed regularly. At the same time, it is recommended to check that all fasteners and plug connections are secure.

An important note: Coil sleeves should always be installed dry. Lubricants or oils attract dust and debris and can even impair smooth operation over time. Modern sleeves are made of self-lubricating materials and do not require additional lubrication.