Originally Posted by zeehag
count on longer than your math says. one d 8, or its equivalent, will take a week on shore power
at 6 amps per hour input. 24/7. good luck.
Lead Acid battery charging is a pretty complicated subject, made even worse by AGM
and gel forms. Smart chargers run the show and they decide when to switch from one charge state to the next based on... whatever their own algorithm is.
In the end the charger holds a bulk charge voltage (that the charger manufacturer thinks is correct) and watches the charge current. When the charge RATE drops below a specific value (that the charger manufacturer thinks is correct) then they drop to the Absorption charge voltage (that the charger manufacturer thinks is correct) and watches the charge current. When the charge RATE drops to an even (much smaller) value then the charger switches to float voltage (that the charger manufacturer thinks is correct).
As you can see, it all really depends on (in no particular order):
1) The max current the charger can supply
2) The charger itself and the algorithms that the manufacturer uses to switch the voltages.
3) The cell chemistry (open lead acid / AGM
4) The battery itself (brand / size)
So there will be no "one size fits all" answer to the question.
also make sure when you charge that your outgo is less than your input. i have met many males who cannot understand this concept.
LOL, don't quite know where to go with this one.
I do have to laugh however. I bought a boat with a charger already in place. It provided two independent circuits of 5 amps (max). As is normal i guess, I have a big red battery selector switch and I was selecting A as my house battery, saving B for my starter battery.
I was running a electric
ice box from walmart which draws 6 amps. Obvious (after thinking about it) my charge on the house battery was dropping. Once I moved the switch to A+B I was drawing current from BOTH batteries but more importantly I was drawing current from BOTH legs of the charger. Now my house battery voltage wasn't dropping any more.
Let me say that 5 amps per leg is pretty darned wimpy. The previous owner did not live aboard!!!