PBO reader Paul Farr wants help in understanding how his marine alternator works. Engine whisperer Stu Davies comes to his aid
Paul Farr writes: “I have a question due to my limited knowledge of electrics. My boat has a Yanmar 2GM20 engine with the marine alternator charging two batteries. The faster the alternator revolves more power is generated which then charges the batteries.
“How is the ratio of the driving pulley to alternator pulley determined ?
“At tickover the alternator is not generating a large amount of power so why don’t manufacturers ‘gear-up’ the alternator to increase the rpm and thereby increase the charging rate. Obviously at max revs the increased charge rate would then be even greater. Please explain.”
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