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Posted: Mon Jan 26, 2009 3:25pm

Post Subject: Alternator regulator

I have had my boat for 6 months and from day 1 I have had 12v power problems. I'm only using about 30ah a night so i bought 3 new 110ah batterys and I ran my engine with an 80ah alternator for about 3 hours a day, within a month the batterys where flat. I went to a local boat yard who told me to fit a "sterling Digital Advanced Alternator Regulator" now after running the engine for about 4 hours a day the regulator says the batterys are charged but by the end of the night the batterys are flat again. I have now been told to buy an "Alternator to Battery Charger" but dont want to keep spending money on things that make no differance. Can you tell me how people who have boats with a fridge, lcd tv and other high consumption items manage?

Alternator regulator

Posted: Mon Jan 26, 2009 4:49pm

Post Subject: Alternator regulator

Dear ?????, I need far more information than what you give and even then the forum that will not allow blank lines or other formatting of text is not the place to try to give you a full answer. I note that you have not filled in your profile so I can not even email you. There are no short cuts to this and as only you know what you use and for how long only you can do the calculations required. Go to (all on one line) and work through the calculations using your own figures. For instance I am very suspicious of 30 Ah per day if you have an electric fridge. The calculations are much simplified but they will serve to give you some idea of where the problem is. You also need to know the output the alternator is capable of delivering as fitted on your boat. Many set-ups do not allow the alternator to deliver maximum output at cruising speed and if you are charging at tickover there is no way your alternator can be considered an 80 amp unit – perhaps 20 to 30 Amps might be more realistic. You need to measure the alternator output, at your usual charging speed within a very few minutes of starting. If you want to email me the charging current as per the above and your worked power audit I will try to advise you. I also need to know the size of your battery bank and what form of charge splitting you are using (if any). You can find my email address in my profile. The answer to your last question is that they ensure their charging regime, methods, alternator size and battery bank size are more or less correct for their particular use of their boats. From what you tell me I suspect you have never got your batteries to anything like fully charged so the discharged parts have sulphated to such an extent that their capacity is only a fraction of what it once was. This is perfectly normal and is the reason why most batteries fail on boats that do not use an auxiliary form of charging. I have seen figures quoted that suggest to fully charge a “typical” battery bank using alternator alone would take between14 & 16 hours. This is because the last (perhaps) 10 to 15% of charging takes an inordinate amount of time and neither of the devices you mention will are likely to affect this to a significant extent. If you can get hold of a charger that does an “equalisation charge” or can get a battery shop to do a manual equalisation charge for you it might make some difference to the sulphation, but I doubt it will be significant. Finally I think you need a mains, marine, multi-stage charger that can be left on all the time. If this is not possible I think you will need to look at a LARGE solar cell or, if its windy enough, a wind generator. Either, when working, will provide the long slow charging needed to get the batteries to close to fully charged – that is in addition to engine charging usually. Tony Brooks

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