New Generation Voltage Regulators

Specific setup instructions and installation procedures are typically packaged with all voltage regulators. When a system is first installed, it is recommended that the Shunt Paralleling Procedure be followed to set up the system. This will allow basic check out and performance to be accomplished. System performance across the entire speed and load range will be displayed and any deviations annunciated.

Should problems arise in a paralleling system, the first step is to identify what is happening. The problem is usually a failure to parallel or a failure to regulate. First, isolate the two channels and to treat them as two mutually exclusive entities. By attaching a voltmeter to the bus, the voltage may be determined and monitored.

New Generation Voltage Regulators

Aid troubleshooting

By Electrosystem's Technical Service Group

June 1999

Prior to starting the engine, turn on the master switch, battery switch, and alternator control switch and verify what voltages are observed at the alternator terminals. Battery voltage should be present at both the alternator battery terminal and field terminal. No voltage should be present at the AUX/STA terminal.

If battery voltage is not present at the field terminal of the alternator with the Alternator Control Switch turned on, the voltage regulator may be suspect. Also, check the LED indicator. If it is on, refer back to the ground fault diagnostic technique mentioned earlier. If the alternator and the field wire check out OK, the voltage regulator is suspect and should be checked on the bench.

If the voltages are correct then the next step is to start the engine and bring it up to approximately 20 percent above normal idle speed. Check bus voltage and record the value along with engine speed and alternator load. If the load is zero, check the bus voltage. If it is still reading battery voltage, there may be no field output from the Alternator Control Unit and it now becomes necessary to check the voltage delivered to the alternator field.

If there is no field voltage check if the LED is lit on the front of the regulator. If the LED is lit, refer to the Ground Fault Diagnostic Procedure for the voltage regulator in question.

Another problem occurs when both channels independently operate correctly, yet fail to parallel properly. This could be either a regulator or a system problem. It is very important to determine which one has occurred. Defective wiring, switches, connections, circuit breakers or even the alternator itself can cause paralleling problems.

Another place to check is the shunt connections to the regulators. These twisted shielded wires should have the shields grounded at the shunt end. Check the connections to make sure that they are not loose or reversed.

Alternator out sensing and indication
In most applications the "Alternator Out" circuit normally experiences little if any trouble. If the indicator light fails to extinguish after engine start with the alternator supplying load current, don't automatically replace the regulator. First check the indicator light for a short to ground.

If the problem is that the lamp remains out even with the engine stopped, check the light bulb or the negative lamp lead for an open connection. Try removing the lamp lead from the regulator and connect it directly to ground to see if the lamp will light. If not, disregard the regulator and concentrate on the lamp, socket or the annunciator assembly.

Another thing to check is the AUX/STA connection in the alternator itself. Check the terminal on the alternator for AC voltage while the alternator is supplying load current.

Using a voltmeter set to RMS and measure the voltage. Normal value expected here, up to 20% of electrical load is approximately 9 volts for a 14-volt system and 18 volts for a 28-volt system. If no output voltage is observed while the alternator is producing output current, remove the alternator and check the internal terminal connection. It may have been disconnected, broken or burned off.

In paralleling systems with two or more power sources, accurate indication of one alternator being off the bus may not be possible with bus low voltage sensing alone. To remedy this, Alternator Out Sensing is used to signal the arrival and departure of each alternator from the load bus. Also, the overall bus voltage may not be significantly different with one alternator off-line. The only place where the lack of participation of an alternator may be rapidly and accurately seen is at the "AUX or "STA" terminals of the alternators. This stator tap reflects the actual load status of the alternator.