03Checking Voltage Drops Tech Tip130006272016

May 24, 2016 (03Checking Voltage Drops Tech Tip) Conducting a Voltage Drop Test, continued Part 2: Alternator Circuit with Carbon Pile (Recommended Method) Alternator Circuit Voltage Drop Test (+) Side Ensure the vehicle’s batteries have been tested and that the terminals have been cleaned and tightened. 1. Ensure the battery is charged to 12.4 volts minimum (AGM batteries 12.6 volts). • • Connect the carbon pile tester positive lead to the B+ stud (output terminal) on the alternator. • • Connect negative lead to the ground at the alternator. 2. Connect the voltmeter (set on low scale) to look for excessive resistance on the (+) side. • • Voltmeter (+) test lead to the alternator output terminal. • • Voltmeter (-) test lead to the battery (+) post. 3. Turn on and adjust the carbon pile to alternator-rated amperage output. 4. Read the voltmeter and record voltage. This is the positive circuit voltage loss. Immediately turn off carbon pile. Alternator Circuit Voltage Drop Test (–) Side 1. With the carbon pile tester still connected, connect the voltmeter to the negative battery cable. • • Voltmeter (+) test lead to the battery (-) post. • • Voltmeter (–) test lead to the alternator ground stud or case. 2. Turn on and adjust the carbon pile to alternator-rated amperage output. 3. Read the voltmeter and record voltage. This is the negative circuit voltage loss. Immediately turn off carbon pile. Calculating Total Circuit Voltage Drop 1. Add positive circuit loss and negative circuit loss to get total system loss. This loss shall not exceed: • • 12-volt system: 0.500 volts maximum voltage loss • • 24-volt system: 1.000 volts maximum voltage loss 2. Replace cables or repair circuits with excessive voltage loss. The higher the reading in each circuit, the bigger the problem. For instance if your readings showed .2 volts loss on the positive circuit and .7 volts loss on the negative circuit, the technician needs to focus on the negative circuit. If the voltage drop exceeds specification, check for corrosion, frayed strands of wire, loose connections or a battery cable gauge that is too small. Part 3: Starter Circuit With Carbon Pile (Recommended Method) Starter Circuit Voltage Drop Test (+) Side Ensure the vehicle’s batteries have been tested and that the terminals have been cleaned and tightened. 1. Ensure the battery is charged to 12.4 volts minimum. • • Connect the carbon pile tester positive lead to the B+ stud on the starter solenoid. • • Connect negative lead to the ground stud on the starter. 2. Connect the voltmeter (set on low scale) to the positive battery cable. • • Voltmeter (+) test lead to battery (+) post. • • Voltmeter (-) test lead to starter B+ post. 3. Load the carbon pile tester to 500 amps and record voltage. This is the positive circuit voltage loss. Immediately turn off carbon pile. Starter Circuit Voltage Drop Test (–) Side 1. With the carbon pile tester still connected, connect the voltmeter to the negative battery cable. • • Voltmeter (+) test lead to starter ground stud or case. • • Voltmeter (–) test lead to battery (–) post. 2. Load the carbon pile tester to 500 amps and record voltage. This is the negative circuit voltage loss. Immediately turn off carbon pile. Calculating Total Circuit Voltage Drop 1. Add positive circuit loss and negative circuit loss to get total system loss. This loss shall not exceed: • • 12-volt system: 0.500 volts maximum voltage loss • • 24-volt system: 1.000 volts maximum voltage loss 2. Replace cables or repair circuits with excessive voltage loss. If the voltage drop exceeds specification, check for corrosion, frayed strands of wire, loose connections or a battery cable gauge that is too small. MIDWESTWHEEL.COM IOWA MISSOURI DES MOINES 1436 E. Ovid Ave. office 515.265.1491 fax 515.265.4120 parts fax 800.314.4329 parts 800.888.0248 CEDAR RAPIDS 200 50th Ave. S.W. main 319.365.4453 fax 319.365.6327 parts fax 877.706.6085 parts 800.332.5435 DAVENPORT 8502 Northwest Blvd. main 563.322.2671 fax 563.322.5940 parts 800.553.1886 SIOUX CITY 1819 4th St. main 712.252.7969 fax 712.252.6149 parts 800.943.3534 CLEAR LAKE 840 Hwy. 18 W. main 641.357.7101 fax 641.357.8190 parts fax 800.548.9674 parts 800.397.5630 KANSAS CITY 5801 E. Front St. main 816.471.1552 fax 816.471.0813 parts 800.821.7402 TRUCK PARTS SUPER STORE TM