Testing Starter Motor Current Draw

Summary

This video provides a detailed, step-by-step guide on how to measure starter current draw in a vehicle, using a basic amp clamp and a battery tester. The process includes checking battery voltage, setting up the equipment, cranking the engine, and observing the current and voltage readings. By monitoring these metrics, you can assess the health of the starter and ensure it's functioning correctly. The video also explains how to interpret the results, with practical insights into what current readings are typical for different engine types, helping users accurately diagnose potential issues with their starter or battery.

Takeaways

• 😀 Measuring starter current draw is a simple yet effective way to assess the health of the starter and indirectly gauge engine health.
• 😀 The battery voltage should be checked before conducting a starter current draw test to ensure accurate results. A voltage around 12.4V or higher is typically good.
• 😀 An amp clamp is used to measure the current drawn by the starter, and it is important to position it correctly around the battery cables leading to the starter.
• 😀 Before starting the test, ensure that the engine cannot start by disabling the fuel system (e.g., removing the fuel pump relay).
• 😀 During the test, the current drawn by the starter will spike initially and then stabilize at a lower value.
• 😀 A drop in voltage will occur as the starter draws current, but it should not go below 10V during the test for the battery to be considered healthy.
• 😀 If the voltage drops below 9.6V during the test, it may indicate a problem with the battery or starter.
• 😀 The typical current draw for a small engine like a Hyundai Accent's 4-cylinder is around 100 amps, but larger engines like V8s or diesel engines can draw significantly more.
• 😀 The key indicators for a good starter test are stable voltage (above 10V) and a reasonable current draw (around 100 amps for a small engine).
• 😀 A current draw of 100 amps for a small 4-cylinder engine like a Hyundai Accent is considered normal, but specifications should be checked for each vehicle make and model.
• 😀 The test is simple and can be done quickly with basic tools like an amp clamp, making it an easy diagnostic procedure for automotive technicians.

Q & A

What is the purpose of measuring the starter current draw?

Measuring the starter current draw helps determine if the starter motor is in good condition and functioning properly. It can also provide insights into the overall health of the engine, although the focus here is primarily on the starter motor itself.

Why is it important to check the battery's voltage before performing the test?

It's essential to check the battery's voltage before performing the test because a weak or low battery might not supply the correct amount of current. This would lead to inaccurate test results. Ideally, the battery should be at around 12.4 to 12.6 volts.

How do you connect the amp clamp to measure current draw?

The amp clamp should be placed around the wire that connects the battery to the starter motor. This allows the clamp to measure the current flowing from the battery to the starter during the cranking process.

What is the significance of ensuring the engine will not start during the test?

It's important to ensure the engine does not start during the test because the test requires observing the starter's current draw while cranking, not during normal engine operation. Disabling the fuel system, such as removing the fuel pump relay, ensures the engine remains off.

What happens to the current draw when the starter motor first engages?

When the starter motor first engages, the current draw jumps to a high level and then decreases slightly as the starter motor begins to rotate the engine. The current eventually stabilizes at a lower value once the engine is cranking consistently.

What is the acceptable voltage drop during the current draw test?

The voltage should not drop below 10 volts during the cranking process. A voltage drop lower than 9.6 volts suggests that the battery or starter motor may be in poor condition, as it indicates a significant loss of voltage under load.

Is a 100-amp current draw typical for a small vehicle like the Hyundai Accent?

Yes, a 100-amp current draw is considered normal for a small engine like the Hyundai Accent's 4-cylinder. Larger engines, especially those with more cylinders or diesel engines, may draw higher currents, such as 200 amps or more.

What is the main indicator that the starter motor is in good condition?

If the current draw stabilizes at a reasonable value and the voltage remains above 10 volts, the starter motor is likely in good condition. However, it’s essential to compare the readings to the manufacturer’s specifications for the specific vehicle.

How can you determine if the battery is good before starting the test?

You can determine the battery's health by checking its voltage. A good battery should read around 12.4 to 12.6 volts. If the voltage is significantly lower, it may not provide enough current for the test, leading to potentially inaccurate results.

What would be considered an abnormal current draw for a starter motor?

An abnormal current draw would be any value significantly higher or lower than the manufacturer's specified range. For a small engine like the Hyundai Accent, around 100 amps is typical, but larger engines may draw more. A very high or low value could indicate issues with the starter motor or the battery.