Electrical generators must have some form of voltage regulation. Without it, the generator will either run as a motor or overload itself and burn up. There are as many systems available as there are regulator designers and the schemes they can think up. That being said, there are a few basic systems that are in use today that would bear scrutiny.Some generators back in the 60’s had a “voltage relay” that was connected to the output voltage. It had a set of contacts that would close if the voltage lowered and opened if the voltage got too high. The relay points were connected to rectified generator output voltage and the resultant switched dc went to the rotor. It was simple, required little maintenance but was somewhat cyclic in its operation as the voltage surged up and down. It was also sensitive to engine speed and sometimes the regulator and speed cycled at the same time and things got a little out of hand.
Modern contractor level portables have two different regulation systems. The small (cheap) ones have two diodes and a capacitor that rectify ac output and feed it to the slip rings. The system works fine as a rough regulator but has some hash in the output frequency wave. The more these units are loaded, the smoother the sine wave gets. These systems are frequency sensitive.
The upper level contractor level portables may have an electronic regulator that rivals that of the RV generators except that most of them also use ac output as the source of power for the regulator as well as the sensing source. This makes the generator less responsive to large load changes.
An intermediate level of voltage regulation was used by several manufacturers during the early 70’s up to the mid to late 80’s. The output of the generator was fed through the coils of a transformer. The secondary of this transformer was fed to a full wave diode bridge and then on the brushes and slip rings and eventually to the rotor. The regulation level was dependent on the ac frequency and an over speeding engine could produce very large voltages.
The two major manufacturers of RV level generators (ONAN and Generac) more closely resemble large commercial generators. That is, they have a separate winding in the generator that provides the power supply for the regulator. Sensing signals are taken from the ac output of the generator and are fed to an electronic regulator. The regulator takes the sensed signal, compares it to an internal reference, decides if it is high or low and sends a corresponding decrease or increase signal to the output rectifiers in the regulator. These SCR’s receive the sensing signal and control the power winding dc output of the regulator. The output is fed to the rotating field (rotor) of the generator through brushes and slip rings to generate a smaller or larger magnetic field thus controlling the output voltage and current of the main generator. Simple, isn’t it.
Modern RV generators use digital voltage regulation. As technology has increased through the years, it has been found that better control and more precise gain and droop parameters could be obtained through digital signals rather than analog controls. The modern regulators do the same thing as their older counterparts but they are more precise in their controlling actions and faster in response to voltage and/or load changes in the generator.
The one thing regulators are not is – cheap. Don’t play with them unless your credit card/s have a really low balance.
Generator Jim