New Generation Voltage Regulators

New Generation Voltage Regulators Aid troubleshooting By Electrosystem's Technical Service Group June 1999 General aviation aircraft electrical systems may be one of the least understood aircraft subsystems when it comes to...

Obviously the alternator cannot build up voltage or produce load current with its field terminal open, but, at this stage, we only want to see if the GFP LED remains off. If it does, since the field lead to the alternator is the only wire disconnected, the alternator itself is suspect. The problem may be a shorted rotor (flying short), a shorted brush, brush holder, etc.

If the LED immediately lights again (either before the engine is started or immediately afterward), the alternator is eliminated as the culprit since it is disconnected and the field lead itself is suspect. Shut down the system and remove the field wire from the harness side of the voltage regulator connector. Again, restart the engine, repeat the above procedure, and record the results. If the LED remains out, the lead wire is shorted to ground somewhere along its length. If on the other hand the LED comes back on, the voltage regulator is suspect and should be removed and tested.

Overvoltage protection
Ground fault protection and overvoltage protection are similar in that both are activated by an intermittent or continuous high voltage surge, which can cause extreme damage to the electrical system and components.

Overvoltage protection provides system shutdown to prevent such damage.

Overvoltage protection circuits in the Electrodelta regulators employ a level of protection for those conditions where too much excitation is provided to the alternator — causing it to "run away." This creates potentially damaging, excessive, output voltage. This condition is caused by either a shorted output transistor in the voltage regulator or the field wiring shorting to the bus either inside or outside the alternator.

The latest overvoltage protection systems are designed around a temperature compensated reference and an integrated circuit operational amplifier. Employing precision feedback control, it functions as a highly accurate, inverse time constant integrator to perform this function. Since its inception, this device and its function have been steadily improved. Today, it is one of the most reliable circuits in use.

In a system, which utilizes multiple alternators, the voltage regulator paralleling circuit assures each alternator carries its share of the load. Two methods are generally used: Field Paralleling and Shunt Paralleling.


Field Paralleling
Field paralleling may be found in two forms: alternator rotors directly connected together with a single regulator or a separate regulator connected to each alternator. Both of these techniques rely on the assumption that equal power to the alternator shunt field will yield equal output currents. This will only happen at equal alternator speeds. Any significant difference will result in the bulk of the current being carried by the channel — with the lowest line resistance. Also, with the first approach, which ties both alternator rotors to a common regulator, an internal rotor problem on either alternator could disable both alternators. The newer style approach utilizing separate regulators with individual field switches provides a means to isolate the two channels.

Proper feeder cable balance (impedance) is extremely important in all paralleling installations, especially field paralleling. Without paralleling, the system must overcome the imbalance in order to share the load. It is recommended that you set the system up in the manner it will be used in the installation without using simulations, if possible. Make sure each voltage regulator is attached to its own alternator — even if extension leads must be used. That way, bus impedance can be taken into account at the time of initial setup.

Shunt Paralleling
Shunt Paralleling is an improved approach. Installing a calibrated shunt in the output of each alternator and connecting them to individual regulators allows each regulator to evaluate the output current from it's own alternator and compare it to the output of the other and equalize it by means of a bus. A further benefit is that the system is more tolerant to imbalances and has the ability to supply dissimilar power to each alternator. This achieves the desired output current balance.

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