--- In [email protected], Eno at Yahoo <enodre...@...> wrote: > > Hi, > > Has anyone any idea how long in general terms it will take a normal > sized alternator (50 amp) to recharge two 110amp batteries, and > recharge the starter battery back to its pre starting level assuming it > was fully charged before starting the engine. > > I know there are a number of variables that would need to be known to > give an accurate answer, but just for general everyday type use and > using normal levels of power, example:- TV for 2 hours, 2/3 (20w) lights > for 5 hours and the water pump and 12 volt compressor fridge. > > As a general guide how long would you think the engine would need to run > to replace the energy lost. > > Thanks >
Unfortunately the question is not the correct one for the information I think you want. The starter battery will be replenished in less than half an hour according to the experts but I doubt that will be fully charged. I would say that unless you are an inveteracy long distance cruiser each day then the chances of you getting your batteries fully charged are close to zero. In four hours the alternator either alone or with one of the fancy additions will get the batteries 80% charged or so BUT from then on the time taken to replace (say) one amp hour gets progressively longer as the batteries near fully charged. It is said that this could take ANOTHER 10 to 12 hours using alternator alone. It is easy getting to 80% of fully charged and fancy charge controllers will shorten this time but it is doubtful if they will make a significant difference to the time needed to get to fully charged. If you do as most boaters without external charging sources do and just concentrate on getting your batteries to 80% fully charged or so then treat them and expendable and expect them to last between two and four years. This is why it is often said that the most cost effective batteries are the cheaper open cell wet lead acid batteries even though the vendors are trying to push us towards sealed cells. Leaving your batteries at around 80% fully charged will result in a gradual loss of capacity caused by a permanent change in the batteries insides. The equalisation charge mentioned in another post will help to mitigate this but not totally resolve it and in any case equalisation charging is far more important for batteries that have been left on float or maintenance charge for long periods NOT those using alternator charging. If you are intent on maximising the batteries life then you need an alternative form of long slow charging that will go on for many hours. A shoreline and multistage charge is probably the best but a fair sized(Watt+) solar panel and controller will also do a fair job on a "holiday" boat whilst it is tied up and you are at home. My advice would be to either get an ammeter and voltmeter fitted and learn how to interpret them OR get a Smartguage but please note that as batteries loose capacity because of that chemical change I mentioned the Smartguage will show 98% charged or whatever based on the actual capacity and not the capacity the batteries were sold with. IF you want a better answer (but still not perfect) you need to work through the calculations you will find in http://www.tb-training.co.uk/Poweraudit.htm Tony Brooks
