How To Bench Test Starter

How to Bench Test a Starter Motor: A Comprehensive Guide

Starting your car's engine relies heavily on a functioning starter motor. When your car refuses to crank, a faulty starter is often the culprit. Before replacing it, a bench test can save you time and money by confirming the problem. This guide provides a detailed, step-by-step process for bench testing your starter motor.

Understanding the Starter Motor

Before diving into the testing process, let's quickly review the starter motor's basic function. It's an electric motor that receives power from your car's battery to rotate the engine's flywheel, thus initiating the combustion process. A typical starter motor consists of several key components:

• Solenoid: This is the electromagnetic switch that engages the starter gear with the flywheel.
• Gear: This meshes with the engine's flywheel to turn the engine over.
• Armature: This is the rotating part of the motor that produces the torque to turn the flywheel.
• Brushes: These make electrical contact with the commutator, supplying current to the armature.
• Commutator: This acts as a switch for the armature windings.

A malfunction in any of these parts can lead to a non-starting vehicle.

Tools and Materials You'll Need

Before you begin, ensure you have the necessary tools and equipment:

• Battery: A 12-volt battery with sufficient amperage (at least 500 CCA – Cold Cranking Amps). Safety First: Always handle a car battery with care to avoid electrical shock or burns. Wear safety glasses.
• Wires with Clamps (Jumper Cables): Heavy-duty jumper cables to connect the battery to the starter.
• Screwdriver: To remove the starter motor from its mounting bolts (if needed).
• Wrench(es): The appropriate size to disconnect the starter motor's battery cables.
• Voltmeter: To measure the voltage across the starter's terminals.
• Multimeter: To check the continuity and resistance of the starter's internal components. (Optional but recommended).
• Work gloves: Always wear protective gear when working with automotive parts.
• Protective eyewear: Essential for safety when working with electrical components.

Step-by-Step Bench Testing Procedure

This section will walk you through the bench testing process:

1. Preparation

Secure the Starter: Find a stable, well-ventilated workspace. Ideally, place the starter motor on a workbench or sturdy surface. Secure it to prevent movement during the test.

2. Connecting the Battery

Connect the Positive Cable: Using a heavy-duty jumper cable, connect the positive (+) terminal of the battery to the large positive (+) terminal on the starter motor.

Connect the Negative Cable: Connect the negative (-) terminal of the battery to the starter motor's case. This will provide a ground connection. Avoid Connecting the Negative to the Small Terminal: Never connect the negative cable to the small terminal; this will damage the solenoid.

3. Testing the Solenoid

Use a Screwdriver (or similar non-conductive tool) to bridge the two small terminals on the solenoid. If the starter motor engages and spins, the solenoid is working correctly. If not, it may require repair or replacement.

4. Testing the Motor

If the solenoid tested well, it's time to check the motor itself. Reconnect the negative cable to the starter's case. Use a screwdriver to manually bridge the large positive terminal to the small positive terminal (on the solenoid). The motor should crank vigorously. If it fails to spin, the motor itself may be defective.

5. Voltage Drop Test (Using a Multimeter)

Measure the Voltage Drop Across the Terminals: This helps determine if there is excessive internal resistance in the motor. With the starter connected to the battery, use a multimeter to measure the voltage drop across the large positive and negative terminals. A significant voltage drop (more than a volt or two) could indicate a problem within the starter.

6. Resistance Test (Using a Multimeter)

This step requires a multimeter capable of resistance measurements. Disconnect the battery from the starter. Measure the resistance of the armature windings and other components according to your multimeter's instructions. Compare your readings to the specifications provided in a repair manual for your specific starter motor. High resistance values typically indicate a problem within those components.

Interpreting the Results

• Solenoid and Motor Working: If both the solenoid and motor function correctly during the bridging test, the starter is likely in good working order.
• Solenoid Failure: If the solenoid fails, it requires replacement.
• Motor Failure: If the motor fails, it's likely the armature, brushes, or commutator requires attention or replacement. The motor might be repairable by a specialist, or a replacement might be necessary.
• High Resistance: High resistance readings indicate internal problems requiring either repair or replacement of the faulty component.

Remember that this is a guide and some starter motors might require slightly different testing techniques. Always consult a repair manual for your specific vehicle's starter motor model if you have difficulty or encounter unusual circumstances. If you lack confidence in working with automotive electrical systems, it's always best to seek professional help.