Alternator Output
- Turn ignition switch to OFF position. Connect positive voltmeter lead wire to alternator B+ terminal and negative wire to ground. See Fig 1. Ensure voltmeter indicates battery voltage. If voltmeter reads zero, an open circuit exists in wire between B+ terminal and battery positive terminal.
CAUTION: During the next step, DO NOT increase engine speed any more than necessary to produce 16 volts. An unregulated alternator can produce excessively high voltage at high speed, which may damage components.
- With voltmeter still connected, start engine and run at idle. Using a screwdriver, ground brush assembly-to-regulator connecting strip to alternator frame. See Fig 2. Slowly increase engine speed while monitoring voltmeter. Alternator should produce at least 16 volts. If alternator produces at least 16 volts, replace voltage regulator. If alternator produces less than 16 volts, go to next step.
- With engine and all accessories off, connect a voltmeter across battery terminals. Record voltmeter reading for future reference (this is base voltage). Install tachometer (if necessary) to monitor engine RPM. Start engine and run at 1500 RPM with no electrical load. Observe voltmeter reading. Voltage should increase 2.5 volts from base voltage reading. If voltage increases, but increase is less than 2.5 volts, go to next step. If voltage does not increase or voltage increases greater than 2.5 volts, repair or replace alternator or regulator.
- Disconnect negative battery cable. Remove output lead from alternator terminal B+. Install a 100-amp ammeter in series between B+ terminal and disconnected output lead. Install positive lead of ammeter to B+ terminal and negative lead to disconnected output wire. Install a carbon pile load rheostat across battery terminals. Be sure carbon pile rheostat is turned OFF or in NO-LOAD position before connecting.
- Install positive lead wire of voltmeter to alternator B+ terminal and negative lead wire to a good ground. Install tachometer (if necessary) to monitor engine RPM. Start engine and run at idle. Adjust carbon pile rheostat until voltmeter reads 13.5 volts. Observe and record ammeter reading.
- Increase engine speed to 1000 RPM. Observe and record ammeter reading. Increase engine speed to 2000 RPM. Observe and record ammeter reading. Compare ammeter readings with specifications in ALTERNATOR OUTPUT CURRENT SPECIFICATIONS table. If alternator output current is within specifications, problem is not in charging system. Check other vehicle systems for cause of problem. If alternator output current is not within specifications, check for shorted or open stator and field windings. Check diodes which may be break down under load.
ALTERNATOR OUTPUT CURRENT SPECIFICATIONS
| Engine Speed (RPM) | Output Current At 13.5 Volts |
|---|---|
| Idle | 30-40 Amps |
| 1000 | 55-65 Amps |
| 2000 | 80-90 Amps |