Tony-B...
Posted: Fri Jun 23, 2017 7:39am
Post Subject:
Adding an extra battery
Solar panels, even modest ones, are excellent at ensuring the batteries are fully charged when you are away from the boat but using them to cover your domestic needs requires a lot unless you are very frugal with electricity. This probably means a gas fridge, led lights, and very limited use of things like computers etc. They will also be very little use for day to day charging during the winter months. We are back to your need to do a power audit and charging calculations so you have a fair idea of the cause of any problem. I have an electric fridge, use a laptop via a 12V power supply and only run a 100 watt very infrequently. This year installed an extra 100 watt horizontal solar panel bringing the total up to 160 watts. Yesterday, a dull day, it produced about 25 A of charge. Even in the previous sunny days it only managed about 40 Ah. You also need some form of battery monitoring so you know when to start engine recharging and when its time to stop engine charging. If you do not monitor the batteries you stand a very good chance of regularly over discharging them and never fully recharging them. That will shorten their life dramatically. Some live-aboards can ruing battery banks in a very few weeks until they learn about recharging an battery monitoring. An accurate voltmeter will tell you when to start charging. Do your level best to never let the batteries rested voltage fall below about 12.3 volts. Basically that is the voltage first thing in the morning with no electrical loads running. Stopping charging so you optimise the batteries life by keeping then fully charges as possible and to minimise fuel use needs an ammeter. Stop engine charging when the ammeter reads about 1 to 2 percent of your battery capacity so in your case say about 10 amps with the engine revving at 1200 rpm as a minimum. Solar is more difficult because its modest output is likely to be producing a low charge because of poor light or lack of panels. Solar may not be the total answer but it will help to some degree. Unfortunately Vetus have fitted gearbox options that not be run for more than about 20 minutes in neutral so if you have this type of gearbox engine charging while stationary may not be an option. You may have to tackle any lack of charging from the other end by limiting your electricity use but that rings us back to a power audit.