When a permanent magnet is used instead of coils, there is no field circuit in the motor. These motors are also used in many different applications. Most newer vehicles have starter motors that use permanent magnets in place of the field coils. A permanent magnet motor has only an armature circuit, as the field is created by strong permanent magnets. This is possible because the shunt coil is energized as soon as battery voltage is sent to the starter. Also, on Ford’s positive engagement starters, the shunt coil is used to engage the starter drive. The field coil that is shunt wound is used to limit the speed of the starter motor. This configuration allows the compound motor to develop good starting torque and constant operating speeds.
#Motor winding types series#
In a compound motor most of the field coils are connected to the armature in series and one field coil is connected in parallel with the battery and the armature. A compound motor uses both series and shunt coils. However, shunt motors may be found as wiper motors, power window motors, power seat motors, and so on. Due to a shunt motor’s inability to produce high torque, it is not typically used as a starter motor. This is because the CEMF produced in the armature does not decrease the field coil strength. A shunt motor does not decrease in its torque output as speeds increase. A shunt-wound field is used to limit the speed that the motor can turn. Shunt means there is more than one path for current to flow. A shunt-wound (parallel) starter motor.Įlectric motors, or shunt motors, have the field windings wired in parallel across the armature. As speed increases so does CEMF, reducing current draw and torque. Graph illustrating the relationship between CEMF, starter motor speed, and current draw. Since current decreases, the amount of rotating force (torque) also decreases.įIGURE. As the motor spins faster, CEMF increases and current decreases. At this time, maximum current flow from the battery through the starter motor will be possible. Notice that, at 0 (zero) rpm, CEMF is also at 0 (zero). Figure shows the relationship between starter motor speed and CEMF. This results in less current flow through the starter from the battery as the armature spins faster. The faster the armature spins, the greater the amount of induced voltage that is generated. This induced voltage will be opposite the battery voltage that is pushing the current through the starter motor. Since a starter motor has a wire loop rotating within a magnetic field, it will generate an electrical voltage as it spins. This decrease of torque output is the result of counter electromotive force (CEMF) caused by self-induction. As the motor speed increases, the torque output of the motor will decrease. This design permits all of the current that passes through the field coils to also pass through the armature.Ī series-wound motor will develop its maximum torque output at the time of initial start. Most starter motors are series-wound with current flowing first to the field windings, then to the brushes, through the commutator and the armature winding contacting the brushes at that time, then through the grounded brushes back to the battery source. Also, many newer motors are designed to be brushless. In addition, many motors are using permanent magnet fields. The motor design is referenced by the method these two components are wired together. The ⚡ field windings ⚡ and armature of the DC motor can be wired in various ways.