Originally Posted by Cheechako
Just keep in mind, even if you have a huge battery
bank... sooner or later you are going to have to refill all those amps!
A larger service
bank size also means it will be more efficient and accept more Ah more quickly from all charging
sources during the boost phase up to 80%.
It takes a bit of very over-simplified maths to prove the point, but a 100 Ah battery
that is discharged to 50% may accept 20Ah in the first hour during the boosts stage, maybe 10Ah in the second hour during the start of the less efficient absorption phase, and the remaining 20Ah in another 5 hour. Doubling the battery size to 200Ah, with the same charging
source of 20 amps, will accept 10Ah into each battery in 1 hour, thatís 20Ah into the bank. In the second hours it will store another 20Ah. Thatís 40Ah replaced in two hours, as compared to 30Ah with a single
bank. In the 3rd hour it may still accept 20 amps into the bank because a single
battery in the start of the absorption phase could accept 10 amps. Thatís 60Ah in three hours.
The key point is that for two hours it is still in the more efficient boost stage where the battery is taking all the current
the charge source can give it. Note that the initial boost charging stage has captured 40Ah in two hours and 60 Ah in three hours. With the smaller bank it could only capture 20Ah in the first hour during boost and 30Ah after the second hour during the start of absorption. The third hour may add another 5 amps. Thatís 35Ah with one batteries and 60Ah with two batteries. So a bigger bank will be more efficient and accept more Ah more quickly from all charging sources.
Since a lot of the time with an engine
or genset you are only charging up to the absorption stage which is about 80-85% then this increase in faster charge times is significant.
Just for the record
we are 24/7 liveaboards in the Med with 1050 Ah AGMs, only 140 watts solar
because we don't want another arch at the back for more solar panels
. A Duogen 400 watt towing/wind gunny, 2 x 100 amp Balmar
alternators - oh and a 280 amp FP DC genset. We run the genset once a week maybe.
We have all the goodies except a washing
machine, and can run the 12000 BTU air on from the batteries via a 2.5 kva Victron inverter
Lifeline AGMs now 10 years old.