How a starter motor works?
A starter motor is the main part of your car starting system, which crank up the engine for the first time before running. People used some "crank handle" to start the engine in the Oldsmobile, but today, all modern car engines use a starter motor. Just turn the ignition key to start, then your car engine will crank.
The starter motor is built from several components were work together with the electromagnetic principle. Here are the main starter motor components for starter motor conventional types
Starter solenoid switch, yoke and pole core, field coil, armature, brush and holder, drive lever, over-running clutch, and pinion gear. For more details about how these components work, you can read "Starter motor parts and functions."
In this post, I will give you some information about how a starter motor works. See the images below for a conventional starter motor type and diagram.
There are three conditions drawn a starter motor works. The first is when the ignition switch is in ST (Starting) position. The second is when the pinion and ring gears engage. And the third is when the ignition switch turns back to the ON position. Below are the details of each condition.
I. Ignition Switch In Starting (ST) position
Starter motor works begin from the ignition switch in starting (ST) position. At this position, electric current travels from the battery through terminal "50" to the hold-in and pull-in coils—the current end to the ground in the hold-in coil. Electric current continues through terminal "C" to the field coils, armature coils, and ends to the ground from the pull-in coil. See the current flow (red lines) below.
As the electric current flows to the ground through the starter motor components, several conditions will happen when the ignition switch is in starting position, such as
- Both pull-in and hold-in coils are an electromagnet, and the magnet will attract the plunger to move to the right side.
- The drive lever will push the over-running clutch and pinion gear to mesh with the ring gear.
- The pinion gear is set to the ring gear and ready to drive the pinion gear correctly.
II. Pinion and ring gears engage
After the pinion gear is engaged correctly to the ring gear, the contact plate behind the plunger connects terminal "30" and terminal "C". When the contact plate is engaged, a massive electrical current flows from the battery through terminal "30", contact plate, field coils, armature, and it ends to the ground. See the current flow (green lines) on the image below.
A massive amount of current flows to the armature, making the armature rotate with high torque and speed. It makes the pinion gear rotates and drives the ring gear to spin and crank the engine.
The pull-in coil loses its magnet because there are no voltage potential differences between terminal "50" and "C". For this reason, hold-in coil magnetic force is still available and keeps the plunger in its position. As a result, the pinion gear can rotate as long as the hold-in coil keeps the plunger in.
Read also:III. Ignition switch in ON
After the engine crank and fire up, the ignition switch normally back automatically to the ON position. In this condition, the current is no longer present at terminal "50". Still, the contact plate remains closed to allow current from terminal "C" through the pull-in coil to the hold-in coil.
The magnetic fields in the two coils cancel each other, and the plunger is pulled back by the return spring. As the plunger pulled back, the contact plate opened its connection.
When the contact plate is open, the high current to the armature coils is cut off, and the pinion gear disengages from the ring gear. All the electromagnetic force and current inside the starter motor components are stopped. So this is the end of the starter motor works.