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The Official Magazine of the Bluewater Cruising Association

Advantages of External Alternator Regulation

Jeff Cote

Pacific Yacht Systems
July 29th, 2015

Alternator regulators were traditionally built into or attached to the back of the alternator and were functionally either producing power or not producing power.  This approach is fine for many applications, particularly with power boats that run their engine and, therefore, the alternator for long periods of time.  Other vessel operators, however, may run their engines for shorter periods of time.  This is prevalent with sailboats that will operate their engine typically for a fraction of their cruising time or for power boaters doing only a short cruising day.  External regulators present several advantages to maximize charging efficiency and shorten engine run times to fully charge the battery bank from the alternator charging source.

Most external regulators take advantage of the digital processing technology to create charging regimes that maximize charging efficiency.  The power output will be tailored to the battery type and follow the three step charging protocol (a bulk phase, an absorption phase, and a float phase). This will charge the battery bank quickly and completely without over charging the batteries.  The battery bank voltage can give the regulator a voltage reading that is more accurate as it eliminates any error that may be introduced due to voltage drop on associated cabling.

There are other small advantages that are gained with external regulators:

  • A soft start up protocol allows the engine to be well started and belts to be well seated in before output power is ramped up.
  • The ability to limit the output from the alternator in cases where full output is unnecessary or undesirable.

However, the main reason for choosing external regulation over internal regulation is efficiency.


PYS Electrical Technician


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