Charging Calculations

[Pete7]

Originally Posted by sailinglegend

Get one that is 25% of your battery capacity - so if yours are 115Ah each - and I couldn't find their actual capacity - then you need a 60 amp alternator. More importantly you need a "marine" hot rated alternator that will actually give you 60 amps when hot. Car alternators are not designed to charge deep-cycle batteries, but they are very cheap. You also need a multi-stage external regulator to charge the batteries properly. Search this forum to find out what this really means!

I'm afraid these items are expensive, you just have to decide what you want to spend your money on.

As SL says its going to get expensive. Add it up first then price up a couple of large solar panels, you might find the solar is the better option.

I seem to remember a cross channel trip when it took our 60 amp alternator 10 hours to charge 30 AH. It was flat calm so we were motoring but it really brought it home how long it takes to get he last few % into a bank which is why most folk don't bother and stop charging short of a full bank.

Pete

[a64pilot]

Originally Posted by Pete7

As SL says its going to get expensive. Add it up first then price up a couple of large solar panels, you might find the solar is the better option.

Particularly if you factor in your not running your engine, burning fuel, making noise and heat and possibly glazing your cylinders

[smac999]

do you have a starting battery as well. or just the two 27's?

is the two 27's one bank, or 2 batteries on a 1-2-all swtch?


keep in mind you are using amps while running too. so if you draw 50ah from the batterys. then start the motor. but are still using 10a (laptop, lights etc) and your alternator is putting out 20a. only 10 is used for charging. so now you're at 5 hours instead of 2.5 unless you turn everything on the boat off.

[Ford Prefect]

So i took the plunge; installed two 100w panels today. Was a pretty simple process all said and done. Thanks for everyone's input!