Now check how many alternator rpms it takes to reach that output. Then figure the minimum engine rpms at which you will be charging. You need a pulley ratio that gives you maximum required output at your minimum engine speed. Make sure that if you punch your engine up to 3,000 rpms, thereby increasing your alternator speed to 12,000, you are not exceeding maximum safe alternator speed. The voltage regulator maintains voltage at a certain level by matching alternator output with the load and the charge level of the battery.
Voltage drops when a load is placed on the power system, or when the battery discharges.
The regulator then increases the amperage output of the alternator until the voltage level is restored, and then tapers output to a level that will sustain that voltage. You should have a regulator that is external, field adjustable, so that you can tailor the settings to your specific power needs and charging patterns. If your engine running time is minimal, you may need a high setting, like 14.4 volts, to get the fast charge you need without damaging your batteries. If you run your engine for extended periods, 13.8 volts may be adequate. Copyright 1999, BoatUS, all rights reserved.