• True RMS trimming on no-battery applications
• Single or three-phase rectified
• Shunt, series or excited field
• Temperature compensation to satisfy lead acid battery requirements
• Low leakage current
• Three-phase designs

Permanent magnet (PM) alternators are usually controlled with either a shunt or a series regulator. In a few applications, small alternators are controlled by simply using a rectifier and the connected electrical load. This is not a practical approach for most systems with more than a 100 watt capability. All PM alternators can be series-regulated, though the costs to meet certain technical requirements can be high. Some PM alternators must not be shunt-regulated, or else serious damage will result.

Here are a few PM Alternator / Regulator - Rectifier basics:

• A rectifier converts an AC wave form to a DC wave form with ripple. A good battery or large capacitor properly connected across the output will reduce the ripple.
• A regulator's function is to reduce the average current through the rectifier to the amount that is necessary to satisfy the operating loads at any given time.
• Regulators using silicon controlled rectifiers (SCR's) may be either series (stops current flow) or shunt (diverts current flow). Shunt regulators adapt more readily to situations where a battery may not be required but where regulation for lights or other loads is required.
• When the voltage across the battery rises above a regulator's set point (nominally 14 volts),
  • the shunt SCR's are turned on as necessary to divert any excess available current away from the battery and/or its loads.
  • the series SCR's are turned off as necessary to block any excess available current from passing to the battery and/or its loads.
• Do not substitute shunt regulators for series regulators without first understanding the alternator characteristics or the engine manufacturer's recommendation. Otherwise alternator/regulator damage may result.
• If measurements are made in applications where there is neither a battery nor a large capacitor across the regulator output, a standard DC meter will give erroneous readings. Under these circumstances a true rms meter with a crest factor of at least six that measures the AC plus DC components of the wave form is needed.
• In order to better satisfy the charging needs of a typical lead acid battery, most regulators are designed with a temperature coefficient to approximate the battery's temperature-sensitive characteristics.

The following comparisons presume that undervoltage (lack of sufficient charge) is the preferred failure mode to an overcharge condition (excessive gassing, sometimes referred to as "boilover") where sulfuric acid leaks and explosive gases may accumulate.