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post #2 of Old 10-12-2004
Sailboat Reboot
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High Output Alternators

In a word - yes. In another word - no. (Sorry, I just had to do that tonight!) If you don''t care how long it takes to recharge your batteries (because you only use them a little bit and then put them back on a shore power charger) then the answer is no - there is no need for a high output alternator. The more complete answer is - the output of the alternator needs to be matched to the size of the battery bank + the load you run during charging (e.g. navigation lights, helm instruments such as wind, speed, depth, radar, chart plotter; refigeration) + the amount of time you are willing to run the engine to charge the batteries + any other potential charging sources (e.g. Wind, Solar, Towed Generator.) Replacing the charge of 50% of a 50 amp hour battery bank takes a lot less time than replacing the charge of 50% of a 2000 amp hour battery bank. So you are really juggling four parameters: output of the alternator, size of the battery bank, how much of the alternator output is not available for charging as it is running other things and how much you deplete the charge on the battery bank.

Confession: Someone responded to one of my posts with the suggestion that I check out Nigel Calder''s Boatowner''s Mechanical and Electrical Manual (second edition.) Well, you know, I''m a guy and a trained engineer and have owned boats for years - what would be the point? But I took it out from the library and it is fantastic. Read Chapter 1 on "Establishing a Balanced Battery-Powered Electrical System. You will be glad you did.

Fair winds and following sea.
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