Posted: Thu Jun 22, 2017 7:01pm

I have a Vetus 4.15 with and 95amp alternator. At the moment I have 3x 110 Ah leisure batteries and one 85 Ah starter battery. My charging system is through a Sterling PDAR unit which was already installed before I bought the boat second hand. I would like to add another 110 Ah leisure battery. Can you see any problems I would encounter? Any advice would be greatly appreciated.

Posted: Thu Jun 22, 2017 8:24pm

There should be no problem charging wise in adding the extra battery but unless you have accurately diagnosed the reason for needing it there could be. If you can produce enough charge each day to put back into the batteries what you have taken out but the simply do not have enough capacity then fitting an extra one will give you extra capacity. If, however, the battery bank has the capacity you need but is causing you problems because you do not charge it enough then an extra battery will be a waste of money and time. You will ruin the four as fast as you may now ruin the three. The fact the boat came with a PDAR fitted suggests someone had "insufficient charging" problems. The standard advice in this sort of case is that you do a power/energy audit of your use of electrical equipment and then the charging calculations that will give you a better idea of where any problem lies. You can find examples of these on TB-Training.co.uk in the maintenance course notes but you need to use your own figures.

Posted: Thu Jun 22, 2017 8:51pm

Thank you for your reply. The batteries I have are just over 2 years old and I suppose we use the boat for about 8 weeks a year. At the moment we are only doing about 4 hours a day motoring so I think we are not putting enough charge back in. Maybe our solution is to look at solar panels.

Posted: Fri Jun 23, 2017 7:39am

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.

Posted: Fri Jun 23, 2017 5:16pm

Thanks for the advice. I have done a 4 hour run today and the Sterling PDAR went into float charge near the end and my voltmeter was right up. In the morning when I turn the Eberspacher on the voltage is about 12.3v and as you know the initial start on that is heavy on juice and it sometimes drops to 12v which it doesn't like and so I run the engine for 5 mins. I do if I can put the gearbox in the ahead position if alongside with about 10000 revs, I never if i can help it run it in neutral for too long. We never used to watch much tv but I've just bought a small flat screen so my inverter is on more than usual, also with this hot weather I expect the fridge is working overtime. I'll look at your power management when I get home and have decent internet. Thanks again.