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Posted: Wed Mar 16, 2011 7:49pm

Post Subject: Battery Charging

I have a bank of 5No. 110amp leisure batteries charged by a 120A alternator. The batteries never seem to get anywhere near fully charged no matter how much cruising I do. Would an alternator regulator improve things and are they suitable for DIY fitting.


Posted: Wed Mar 16, 2011 9:06pm

Post Subject: Battery Charging

First of all the average output of that alternator over up to four hours is probably only 60 amps and it falls as you extend the charging time. Secondly it takes between 10 and 16 hours to fully charge a battery so most of us accept about a 80% charge and accept we will gradually loose battery capacity to sulphation so once the batteries are perhaps two years old then may only have 50% or less of their original capacity. It is vital that you work through the power audit & charging calculation sin then articles section of my website ( This will give you some idea about how to improve things on your particular boat with your use of it. If (its a big IF) your charging system is in decent order with minimal voltdrop on it And if your alternator's regulated voltage is 14.4 or above then an advanced controller is unlikely to make a significant difference. If it does then it is probably hiding another fault. If the regulated voltage is less than that it may well make a difference but I would question the economics on a modern engine. Most advanced regulators being fitted to most alternators require a modification to the existing voltage regulator or circuit. I would hesitate to advise someone I do not know to attempt it but some suppliers will supply an already modified regulator at a cost. The fitting instructions are normally clear enough. Without being given your symptoms I suspect you are suffering from sulphated batteries and an advanced controller will do nothing significant to cure that. Tony Brooks

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