High-Out­put Al­ter­na­tors

Soundings - - Workings -

Most en­gine man­u­fac­tur­ers de­liver the elec­tri­cal sys­tem so that the in­staller just has to hook up a crank­ing con­duc­tor and en­gine block ground ca­ble. Once that’s done, whichever bat­tery was se­lected for start­ing be­comes the one that the al­ter­na­tor is charg­ing. All re­turn cur­rent runs through the en­gine block and al­ter­na­tor case to com­plete the cir­cuit — cur­rent flows through the whole cir­cuit, and volt­age is con­sumed. (Starter mo­tors sim­i­larly use the case as a grounded con­nec­tion.)

When we up­grade an al­ter­na­tor to pro­vide greater charg­ing ca­pac­ity, we can al­ter the cur­rent path to best suit the in­creased cur­rent flow. In most cases, di­rectly charg­ing the house bank with all avail­able am­per­age and al­low­ing for the mi­nor charg­ing of the start­ing bat­tery af­ter­ward is the most ef­fi­cient way of re­plen­ish­ing bat­ter­ies.

How­ever, sev­eral fun­da­men­tal sys­tem changes have to be made to the out­put wiring from the al­ter­na­tor to meet re­quired stan­dards. Con­duc­tor size must be in­creased to re­duce volt­age drop and en­sure safety, a cal­cu­la­tion made from max­i­mum ex­pected cur­rent and dis­tance along the con­duc­tor (and back). Over­cur­rent pro­tec­tion is now re­quired for this con­duc­tor be­cause we are tak­ing it off the starter mo­tor ter­mi­nal. Crank­ing con­duc­tors are not re­quired to have over­cur­rent pro­tec­tion, but in­stead of shar­ing, we are pro­vid­ing a new con­duc­tor that goes to the house bank, so we must in­stall a suit­able fuse or cir­cuit breaker. This pro­tec­tion is also re­quired at Paul Mirto is a dig­i­tal il­lus­tra­tor, long­time boater and for­mer Coast Guards­man. mir­toart.com

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