>> Please note that the alternator charges at very low rate >>when the engine is idling. It will only provide decent charging current >>at above 2500 RPM. Is this true? I thought we gave up generators for alternators so they would charge at idle--so I spent some time with Google trying to understand this. Chart of RPM vs amps: http://www.fordmuscle.com/archives/2004/07/6GAlternator/index.shtml Look like a pretty flat "curve" on this. Balmar (marine alternators) with very good tables: http://www.balmar.net/PDF/Alternator-Regulator%20Guide.pdf A table that seems to contradict these: http://www.uuhome.de/william.darden/carfaq5.htm What I think I understand is that where generators were run at 1/2 engine speed (so they wouldn't self-destruct), alternators are typically run a 2x engine speed. The higher the output (amps) of the alternator, the more "curve" to the curve. The lower the output, the flatter the "curve." Here's Balmar data for an 80 amp alternator (vs the 90 amp used in most Vanagons, except early ones--which were 45 or 65 amp!): rpm amps 2000 56 3000 74 4000 82 5000 85 (These are alt rpms, so about 2x engine rpms.) So in this case, reving the engine to 2000 rpm (4000 rpm alt) gives ~45% more amps than idle. To me, that means idle isn't so bad after all. Anyone with certain knowledge of this stuff wanna comment? Richard A Jones Boulder, Colorado |
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