QI am looking to buy a three-stage battery charger for my 3 x 120 Ah domestic deep cycle batteries. Can you advise the correct size? I am thinking of 10%, so around about a 40A charger.
MOONFLEET1, from the CB website
ATONY REPLIES… It rather depends upon what you intend to do with it. If you are going to run it 24/7 on a shoreline then a much smaller one (say 10 amps) might be perfectly adequate and be kinder to the batteries. If you also want it to cover the demands of mains equipment then you might need a much larger one simply to ensure the inverter draws from the charger rather than from the batteries. If this is to run from a generator, you might need a higher output one to minimise the charge time, but for most of the time it would be delivering far less than its rated output.
When we were in Liverpool a couple of years ago, I used an 8-amp charger and it more than kept 3 x 110 Ah batteries charged on a simple 12-volt boat. A 40-amp charger will do the job but you might be spending more than you need to.