The starter hair-pin motor armature is an internal component of a starter motor. It plays a big role in the working of vehicle starting systems. 

The starter motor armature consists of windings, an iron core supported on a shaft, and a commutator. 

Starter motor armature function

Starter motor armatures exist in a wide range of sizes. It depends on the intended application, which can be low-power or heavy-duty. They all operate identically, though, by using an electric current to cause rotation.

The starter hair-pin motor armature contains a slotted iron core around which many loops of conductor wire are wound. When current flows through these windings, a magnetic flux is generated.

The coils on the armature end in a part called a commutator. The commutator itself is made up of segments. Each segment is a conducting surface, and insulated from the others. The segments allow different sections of the coil to receive current at different times during rotation.

Surrounding the starter armature assembly is a magnetic field from the stator. The motor stator can be coil windings on a magnetic core or a permanent magnet. When the field is from an electromagnet, the wires connect to the battery.

Here is what happens when the ignition key is turned, and what culminates in the starter armature rotation.

As the armature turns, the commutator also turns with it, causing the sections in contact with the brush to change. That results in the next section conveying current to the armature windings. The adjacent part of the coil energizes, and the process repeats.

Starter Armature

The core of the starter hair-pin motor armature is its largest part. It consists of thin circular and slotted layers of iron, also called laminations. The pieces are insulated from each other to reduce eddy currents. If it were a continuous block of metal, eddy currents would occur and waste electrical energy in the form of heat.

Starter hair-pin motor armature core

Iron is used for the armature core due to its excellent magnetic properties. It produces a strong magnet, which is necessary for the amount of torque required to start an engine. All around the core are slots to secure the coil windings. The slots run the length of the armature assembly.

Starter hair-pin motor Armature Coil Windings

Looped around the core are the starter hair-pin motor armature windings. These are fairly thick copper wires that conduct current with the least resistance. To prevent shorting and other problems, the starter armature coil wires feature a thin layer of insulation.

The coil windings of a starter motor armature end in the commutator where they attach to specific segments. This enables the changing of electrical connections with the windings. It also allows the reversal of polarity and, therefore, the continuity of armature rotation.

Starter armature coil windings

As we have seen, the coils, together with the iron core, have to produce a strong rotational force. For that reason, several different loops are used, which can be as many as 30 in a single core. Each coil also features many turns of the wire to help increase the strength of the magnetic field and, therefore, torque.

Starter Armature Windings Pattern

Electric motor manufacturers use three different ways to wind armature wires: Shunt, Series, and Compound.

Series Winding

The field or stator coils are in series with those of the hair-pin motor armature. Current follows a continuous path from the field wires, brush, commutator, to the armature windings and back to the brush on the other side.

Series wound motors produce a strong rotational force immediately after starting. That drops considerably as the speed of rotation picks up. This arrangement suits the requirements of car starting systems where initial torque matters the most. Most automotive starter motor armatures are, therefore, shunt wound.

Shunt winding

The hair-pin motor armature coil features parallel connections with the field coils. This type of winding pattern does not produce a high enough torque. However, an increase in the speed of rotation does not cause the torque to reduce. Because of the low force generated by the armature, shunt wound motors are not suited for starting systems. Instead, they are mostly used in vehicle accessories.

Compound winding

In this hair-pin motor armature wiring pattern, a section of the armature coils are connected with those of the stator (or field coils) in series. The other section is connected in parallel. The pattern allows the motor to have the benefits of both shunt and series patterns. As a result, the armature torque remains high enough and constant throughout the motor operation.