Did you know that the car starter motor draws the most battery voltage in your entire car?
Despite its small, compact size, it consumes more power than the headlights, fuel pump or air conditioner in a burst!
In this article, we’ll go through the inner workings of the car starter motor and break down its basic components. We’ll also go through the different starter motor types and answer some related FAQs.
This Article Contains
- How Does A Starter Work?
- What Are The Components Of A Starter Motor?
- Types Of Starter Motors
- 9 Starter Motor FAQs
- What Is The Starter Motor?
- Why Are Starter Motors Required?
- Where Is The Starter Motor Located?
- How Long Does The Starter Motor Work?
- How Does A Starter Motor Fail?
- What Are The Symptoms Of A Bad Starter Motor?
- Where Do Car Battery Cables Connect?
- What Is The Neutral Safety Switch?
- How Can I Get My Starter Motor Fixed?
Let’s dive in.
How Does A Starter Work?
To crank the engine, the starter motor uses a small pinion gear to rotate the larger engine flywheel (or flex plate).
The engine flywheel has a ring gear around its edge. The starter pinion gear is designed to mesh temporarily with the flywheel ring gear — just enough to get it spinning.
What exactly happens?
The starter motor has two circuits — the starter motor circuit and the control circuit.
The starter circuit carries the large currents from the battery to drive the starter motor, but doesn’t immediately power up when the ignition key is turned. For this, it needs the starter solenoid because there’s too much power for a small switch (like the ignition key) to handle.
So instead, the battery activates the control circuit — which energizes the solenoid, often through a starter relay and neutral safety switch.
The solenoid is an electromagnet that acts as the starter switch.
When energized, it does two things:
- The solenoid draws a plunger down its center, closing two metal contacts. This completes the starter circuit, allowing heavy current from the battery to flow to the starter motor.
- Simultaneously, the plunger engages a lever fork which pushes the starter pinion gear outwards to mesh with the larger flywheel ring gear.
Since the starter circuit is now complete, the starter motor powers up and turns the pinion gear which rotates the flywheel. The flywheel cranks the engine into a running sequence, where the pistons move, the air-fuel mixture is released, the spark plugs fire and so on.
As the engine turns over, the flywheel picks up rotational speed, and return springs retract the pinion gear. This is important as the backdrive from the flywheel can damage the pinion gear and the starter motor.
Note: ‘Backdrive’ is when the flywheel moves faster than the pinion, “driving” it instead of the other way round. This system is called a Pre-Engaged System because the pinion “pre-engages” the flywheel before turning.
Next, let’s break down the starter motor into pieces.
What Are The Components Of A Starter Motor?
Here’s a look at the basic components of a starter motor.
1. Field Coils
The starter motor housing holds 2-4 field coils, which surround the armature. The field coil array produces a strong, stationary electromagnetic field as current from the battery passes through.
The armature is an electromagnet fixed onto the starter drive shaft (also called the armature shaft). It’s made of a laminated soft iron core wrapped with numerous conductor windings.
The armature shares an axle with the commutator, which provides the current to generate an electromagnetic field. The reaction between armature and field coil magnetic fields is what rotates the armature.
3. Commutator And Brushes
The commutator is located at the rear of the starter motor housing. It’s made of two plates attached to the axle of the armature shaft. Carbon brushes connect to each plate, providing an electrical connection for the armature windings.
The starter solenoid functions as a powerful electric relay.
A typical starter solenoid has a small connector for the starter control circuit wire (connected to the ignition key) and two larger terminals; an input terminal for the positive battery cable and an output for the cable that powers the starter motor itself.
The solenoid usually has two coils of wire wrapped around a movable plunger.
The coils do this:
- A strong closing coil draws in the plunger
- A weaker coil holds the plunger in position — when this happens, current is removed from the strong coil, saving some power
When activated through the control circuit, the solenoid also extends the pinion gear to mesh with the flywheel ring gear, closing the starter circuit to send battery voltage to the starting motor.
The plunger works with the solenoid to connect battery power to the starting motor and pull in the lever fork.
7. Lever Fork
The lever fork is attached to one end of the plunger. When the plunger moves into the solenoid core, the lever fork pushes out the pinion gear to mesh with the flywheel ring gear.
8. Pinion Gear (Drive Gear, Starter Gear)
The pinion gear turns the engine flywheel ring gear. It’s also called a drive gear or starter gear and is part of what’s sometimes known as a starter Bendix drive.
It’s attached to the armature drive shaft, often through an overrunning sprag clutch. The sprag clutch allows the pinion gear to transmit drive in only one direction.
So, if the pinion stays engaged with the flywheel (which can happen if the ignition key isn’t released when the engine starts), the pinion will spin independently of the drive shaft. This prevents backdrive and damage to the starter motor.
It’s important to note that the starter motor has evolved over time, and we now have various types of starters.
Let’s take a look.
Types Of Starter Motors
Here’s an overview of some common types of electric starter motors:
1. DD – Direct Drive
The DD is the most common type of starter motor and is usually solenoid operated. The drive gear (pinion gear) on the DD is attached directly to the armature, thus “direct drive.”
2. PLGR — Planetary Gear
The PLGR starter motor uses a planetary gear assembly located between the armature and the pinion gear. The planetary gear assembly allows a gear reduction which increases torque at a significantly reduced starter motor speed, and in this way, cutting current demands.
3. PMGR — Permanent Magnet Gear Reduction
The PMGR starter motor was designed to lessen the weight, ease construction and reduce heat generation. Instead of using the heavier field coil assembly, the PMGR employs permanent magnets.
4. PMDD — Permanent Magnet Direct Drive
As its name suggests, the PMDD is a direct drive starter motor that uses permanent magnets in place of field coils.
5. OSGR — Off-Set Gear Reduction
The OSGR starter motor was designed to work with high speed and low current. Its internal gear sets are offset, meaning the drive gear and starter motor rotate on different axes.
Now that we’re familiar with how a starter motor works, let’s go through some FAQs.
9 Starter Motor FAQs
Here are answers to some starter motor questions you may have in mind.
1. What Is The Starter Motor?
The starter motor is a device used to turn over or “crank” an internal-combustion engine. It typically consists of a starter solenoid and a powerful motor starter.
The electric starter motor is commonly found in petrol or small diesel engines, but it isn’t the only kind.
Other types include the:
- Inertia starter: This is a variant of the electric motor starter used on aircraft with large radial piston engines
- Hydraulic starter: This offers a sparkless, reliable method of engine starting for applications like remote generators or lifeboat propulsion engines
- Manual starter: This consists of an on/off switch and an overload relay, and is typically used for smaller motors like small pumps and power saws
2. Why Are Starter Motors Required?
The internal combustion engine runs on a feedback loop, relying on inertia from its cycles to run on its own. An engine needs air, fuel and a spark to run unassisted, but something has to start the cycles — which is where the starter motor comes in.
Once the starter motor has initiated engine function, rotational energy from the engine feeds off a drive belt that powers different components like the alternator or power steering pump.
3. Where Is The Starter Motor Located?
In most vehicles, the starter motor is bolted to the engine or transmission. An easy way to find it is to follow the thick cable from the positive battery terminal.
4. How Long Does The Starter Motor Work?
The starter motor’s electrical components are typically designed to operate for 30 seconds at the most, before overheating.
Most manuals instruct for a pause of at least 10s after each 10-15s of engine cranking if an engine doesn’t immediately turn over.
And if it still won’t crank, it might be time to call in your mechanic.
5. How Does A Starter Motor Fail?
A faulty starter can stem from several issues.
Here are some causes that can manifest a starter problem:
- Burned, worn out, or dirty solenoid contacts stop the starter circuit from closing
- Worn-out carbon brushes fail to deliver current to the starter motor
- The pinion gear doesn’t mesh correctly with the engine flywheel
- Insulation on the armature winding starts to break down, reducing the starter’s ability to generate torque
- The starter neutral safety switch fails or is out of adjustment
- The ignition switch fails, so the solenoid isn’t activated
6. What Are The Symptoms Of A Bad Starter Motor?
Here are the typical symptoms you’ll encounter if you have a bad starter motor:
- Clicking noise: Your car battery is fully charged, but there’s only a clicking noise when the ignition key is turned. This is the sound of the starter solenoid engaging, but the starter motor doesn’t power up.
- Grinding noise: The starter motor runs but fails to turn over the engine, and there’s a painful grinding noise. This could be the sound of the starter pinion gear failing to mesh correctly with the engine flywheel ring gear.
7. Where Do Car Battery Cables Connect?
The negative (ground) battery cable attaches the negative (-) battery terminal to the engine cylinder block or transmission. The positive battery cable links the positive (+) battery terminal to the starter solenoid.
The starter motor needs a very high electric current to turn over the engine. So, a faulty connection on even one battery cable (like a loose terminal connector or corroded one) can cause the starter motor to fail.
8. What Is The Neutral Safety Switch?
Most cars incorporate a safety switch, which electrically sits between the ignition key and starter solenoid. It forms part of the starter control circuit, which includes the ignition switch and starter relay.
The neutral safety switch ensures that cars with automatic transmission aren’t started in driving gear. It limits starter motor operation to when the automatic transmission is in the Park or Neutral position.
In some manual transmission cars, the engine can only be started when the clutch pedal is depressed.
9. How Can I Get My Starter Motor Fixed?
The starter system plays a vital role in your vehicle’s engine function. If your car won’t start, you do have the option of troubleshooting it yourself.
However, a starter problem can often mimic that of a bad battery or bad alternator — and are sometimes interconnected. To ensure all your starting issues are resolved, it’s best to let a professional see to it.
And you’re in luck, as RepairSmith is readily available to help you out!
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Here are some benefits:
- Vehicle maintenance and repairs can be made right in your driveway
- Expert, ASE-certified technicians perform auto inspection and servicing
- Competitive and upfront pricing
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- All vehicle repairs and maintenance are completed with high-quality tools and replacement components
- RepairSmith provides a 12-month | 12,000-mile warranty for all repairs
For an accurate cost estimate for a starter motor replacement, just fill this online form.
The starter motor is a neat, little device that forever eliminated the need to hand crank a car engine. It’s also a component that rarely fails, despite the amount of power it harnesses each time it starts your car.
However, if you do run into a starter problem, don’t worry.
Just get hold of RepairSmith.
Their ASE-certified mechanics will be in your driveway in no time to help you get that starter issue fixed up!