![]() 80 amps at a nominal 12 volts) and generally less than this. In both cases, the average charge rate into battery banks is typically no more than 1 kW (approx. In practice, cruising sailboat owners at anchor often end up running their main engine, or an auxiliary generator powering a battery charger, for two to three hours a day, while powerboat owners run a generator lightly loaded for even longer. You either run a fossil-fueled engine long hours lightly loaded to periodically fully recharge batteries or you kill the batteries in short order. Gel cells have a moderately higher charge acceptance rate, and AGMs an even higher rate, but nevertheless all suffer from low charge acceptance rates at higher states of charge. Unfortunately, the charge acceptance rate at 50 percent state of charge is, at best, 40 percent of a wet cell battery’s rated capacity, declining to 15 percent at 80 percent state of charge, and just a dribble of amps above 90 percent state of charge. In order to avoid premature failure, the general rule of thumb is to prevent discharges below 50 percent state of charge, and to regularly charge to 80 percent state of charge, with periodic charges to 100 percent state of charge. Ducting away the hot air from the alternator helps it maintain a higher output. However, if batteries are operated on a regular basis at these kinds of states of charge, they fail prematurely.Ĭalder found that high output alternators also produce substantial heat that can reduce output. The only way to pump relatively large amounts of energy into a battery bank in a relatively short period of time is to operate the batteries in a well discharged state - say between 50 percent state of charge and 20 percent state of charge. As a conventional battery comes to charge, its charge acceptance rate steadily declines until it is accepting little charging current, regardless of the power that is available. Both classes of boat tend to have a more-or-less permanent energy deficit. It is also a problem for any powerboat that spends a significant amount of time at anchor. This is a particularly acute problem on cruising sailboats which, much of the time, have little need of an engine for propulsion purposes and therefore have extremely limited engine run hours available to power an alternator for battery charging. ![]() This guide shows how to view the below listed amp, gauge and wire feet charts.For as long as I have been experimenting with boat electrical systems, the limiting factor in DC systems design (and, indirectly, much AC systems design) has been the low charge acceptance rate of traditional lead-acid batteries (whether wet cell, gel cell or AGM). alternator, battery, etc.) can produce more power than the amount being consumed by the DC device. You will also need to know that your power supply (e.g. Wire size by gauge, ampers draw and maximum feet of wire.Īs in most electrical situations it is important that you know the maximum amp draw of the device being installed. We have a chart for 12-volt, 24-volt, 36-volt, 48-volt and 72-volt applications. Don’t worry, calculating the wire size is made easy with the wire size guides below. The size of wire required for a given task depends on the voltage being used, the amount of amps required and also the distance that power is being transmitted. When installing DC powered appliances and accessories it’s important to use the proper size wire.
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