--- In [email protected], Bruce Napier <br...@...> wrote: > >
snip > > > If you are worried about minimising sulphation you either need a > > shoreline & multi-stage battery charger or a decent sized solar > > array and/or a wind turbine. > > > Indeed, and much as you said earlier in the same edition. This is of > course the problem for folk like us, with rare access to a shoreline, > and subjecting the batteries to a charge/discharge cycle every day, > seldom getting near a full charge. > > The guys who supplied the batteries to Felonious Mongoose (name's > escaped me for the moment) reckoned that to avoid sulphation, a lead > acid battery needs regularly to undergo a charge at 2.4 V per cell > (ie 14.4 V for a nominal 12 V battery) for four hours continuously > to reduce sulphation to a minimum. > > It's for this reason that Sanity Again will have bog standard open > cell lead acid batteries rather than traction cells - without the > potent charging system of the hybrid drive, there's no way we could > keep the cells adequately charged, and so they will sulphate > regardless, and we may as well reconcile ourselves to a regular > replacement regime. > > > All the best > > Bruce > I am afraid that 14.4v is not as cut and dried as the chap implies. Some sealed cells (mainly gels)should not be charged at more than about 13.8 volts and some designs of AGM have similar voltage limitations. Sticking with ordinary wet lead acid batteries. 14.4 volts is probably the optimum for efficient charging (that is maximising the conversion of lead sulphate to lead oxide and minimising wasting current in producing heat and splitting the water in to H & O). However the four hour figure is a pretty empirical one because on a "typical" system (whats typical?) 4 hours is a figure that will ensure most systems are charged to between 80% & 90% of fully charged. The other 10 to 20% will take very much longer (say up to another 12 hours) and boosting the charging voltage may not help despite what the ammeter may be saying. It is very unlikely that a cruising boat can ever fully charge its batteries from the engine so they WILL gradually sulphate. AS you say, batteries are best looked at as consumables unless you can organise ,long term, low rate charging to deal with that last 10 to 20% fairly quickly after the discharge. Tony Brooks
