Part of Lesson Plan: **Perform a battery, starter, charging system test using the VAT-40 (updated) by Eli Jaramillo
Activity Overview / Details
Charging system load test: Using the same lab vehicle and VAT tester you used for the starting system test, you'll now be demonstrating the charging system test.
With the vehicle engine running at about 2,000 RPM, you’ll be applying an AMPS load on the alternator to obtain the highest AMPS reading possible without causing the battery voltage to drop lower than 12 volts. A low amperage output reading could mean the alternator or regulator may need replacing. For this test, you’ll continue use of the VAT machine.
- Student Worksheet : Testing a Charging System
- One lab vehicle with all systems working
- VAT machine
- Instructions for that tester if needed
Pre-checks/set-up on the lab vehicle :
Under your supervision, have select students perform the steps below.
- Turn off all switches, lights, accessories, make sure all doors are closed.
- Perform a visual inspection on the battery and cable connections.
- Check for cracks, corrosion, other damage to the battery.
- Write down the alternator output rating specification for the vehicle you’re working on: ______ amps.
NOTE: For the spec needed above (step 4), choose two students to look it up on-line or refer to the vehicle service manual for reference.
- Turn the tester large LOAD control knob fully counter-clockwise.
- Turn TEST SELECTOR to #2 CHARGING.
- Turn VOLT selector switch to INT.
- Use the Zero-Adjust control to adjust the AMPERES (ammeter) to read ZERO.
- Connect the large alligator clamp tester leads, red to battery positive, black to negative.
- Clamp the green inductive ammeter pickup around the negative vehicle battery cable.
Set-up: Vehicle running amps test:
- Turn the ignition switch to ON, don’t start the vehicle.
- Read the amount of discharge on the ammeter. This reading is the vehicle ‘running amps’, or the current the alternator must supply to the vehicle before charging the battery.
- Write down the above ' running amps' reading. It's usually around 6 amps.
Perform charging system test:
- With the engine running at around 2,000 RPM, turn the large LOAD control knob slowly clockwise to obtain the highest ammeter reading without causing the voltage to drop lower than 12 volts.
- Write down this reading: _______ Now add the running amps reading you wrote down above.
- Write down your final reading: _______
This reading should be within 10% of the alternator’s
Based upon results from the above test: Ask the class for their opinion: Within spec?
Materials / Resource
- Worksheet: Testing a Charging System [ Download ] Worksheet used by students in the lab.