Comments on: How big an alternator do you need ? http://www.altendorff.co.uk/archives/107 sailing; navigation; electronics; computers; boat maintenance.. Sat, 04 Sep 2010 15:08:13 +0000 hourly 1 http://wordpress.org/?v=3.0.1 By: wackyracer http://www.altendorff.co.uk/archives/107/comment-page-1#comment-5764 wackyracer Sun, 20 May 2007 10:34:23 +0000 http://altendorff.co.uk/archives/107#comment-5764 The question is how big an alternator...surely this depends on the rate and amount of discharge of the batteries - which differs from owner to owner. Normally a saling boat (unlike a car) will deeply dicharge its batteries so the alternator must be big enough to recharge as quickly as possible on the basis that a sailor wants to run the engine as little as possible. A battery that is 50% discharged will will accept a rate of charge 25% higher than its rated capacity ie. a 200Ah battery will accept charge of 50amps. But as the battery comes up to charge the acceptance rate declines. By the time the battery is up tp 70% of full charge its acceptance rate will be down to 10/15% of its rated capaciy. The battery will begin to heat up an gas if the charger continues to run at the same rate... The question is how big an alternator…surely this depends on the rate and amount of discharge of the batteries – which differs from owner to owner.

Normally a saling boat (unlike a car) will deeply dicharge its batteries so the alternator must be big enough to recharge as quickly as possible on the basis that a sailor wants to run the engine as little as possible.

A battery that is 50% discharged will will accept a rate of charge 25% higher than its rated capacity ie. a 200Ah battery will accept charge of 50amps. But as the battery comes up to charge the acceptance rate declines.

By the time the battery is up tp 70% of full charge its acceptance rate will be down to 10/15% of its rated capaciy.

The battery will begin to heat up an gas if the charger continues to run at the same rate…

]]>