Originally Posted by delmarrey
Besides, charging a battery too fast burns/boils the plates, shortening the life of the battery(s).
I am sure that 90% of the folks wanting / needing advice get frustrated by the "it depends" responses when all they want is the baby, not the pain, so to speak. Experts and there are many here, try to drag out a little more information in order to provide a precise recommendation. Then someone makes a recommendation or a comment and the thread devolves into a techie argument with pleukerts formulae and all kinds of stuff.
At great risk of that and further demonstrating my own ignorance here goes...
There are two "common" battery constructions the average boater will see - there are others. Wet and sealed. You can add fluid to the wet battery. A true sealed battery you cannot.
Wet batteries usually have three duty ranges - deep cycle, start and there are some general duty type that are supposed to be in between.
Sealed batteries are generally glass mat or gel. Sealed batteries are not generally deep cycle batteries.
Charging a battery makes heat. The faster you charge the more heat you make. Heat can boil or gas off the liquid in wet batteries and sealed batteries. When a sealed battery overcharges it may pop off the vent permanently reducing the performance or even permanently damaging the battery cuz you can't add fluid. We desire to charge "fast" especially house batteries while the engine
is running, wind
is blowing, sun is shining or shore power is connected. Deep cycle batteries are constructed with heavier plates inside that are more tolerant to high charge rates.
However, heat also reduces the ability of the battery to accept a charge. This shows up as the charger "thinking" the battery is charged and it stops charging. The reasons are technical and the average boater doesn't need to know why.
The wet deep cycle is a good house battery, we'd like to discharge it a lot and charge it fast when we can. It requires maintenance
in terms of checking water
levels. The windlass
and starter take a lot of power out "quickly" but after an anchor
pull or engine
start the battery is really not depleted much and we aren't gonna use the starter again real quiick or pull the anchor
again real soon. We can charge it slower. A sealed battery usually works well for this as it is can be cheaper, lighter and requires no maintenance
However because they are different construction, ideally they need two different charge rates. The "heavy" deep cycle can take a faster charge.
In a big system it makes sense to have two charging rates. The batteries are very expensive and charging them wrong can deplete their lives by years! So they will have two different charging schemes.
The average small boat with 2-3 batteries will likely have all sealed batteries solving the maintenance need and eliminate the desire for two charging systems. Although with one bank deep cycling and the other not a there are a couple of other problems created but easily solved
and more often than not ignored albeit at a lower total battery life.
Fnally we get to talk about charging them! Because of the heat, and the battery "tricking" the charger two stage and 3 stage chargers are now common.
Bulk charge - it is general advised that the maximum charge rate is total battery capacity divided by 10. A 200ah battery system should be charged at 20amps. This is the fastest you should go. For a depleted battery it will accept this charge and the heat will not be a problem.
Absorption - At some point (80? charge) the heat and resistance will start becoming a problem. How the charger knows this is not important. A good 3 stage charger does and starts reducing the charge current
. The more expensive the charger the more sophisticated can be the sensing technology.
Float - at the "end" of the absorbtion cycle a 3 stage charge goes into float to "perfectly" top up the battery. Or so they say!
You can see if two chargers were in a system each one thinking they were in a different phase of charging it would be a problem. Really smart chargers from the same company (usually) can work together if the company advertises them to.
You have to know how big your battery capacity is
You have to know what types of batteries you have
You have to know how smart your chargers are and how many phases there are and now much charge current
they are gonna provide in the bulk phase. Smart chargers can be switched for when the phases kick in depending on battery type (see conclusion 2)
Don't stick two "not so smart" pep boys 2 stage chargers together - and if you have one of these with the "quick" charge position, reread the above and think about whether quick charging your $300 agms at the 200 amp setting is a good idea...
A note on solar
. On the average boat described above and in the amounts that the owner might install the charge these guys add is minimal compared to the alternator
or battery charger. In general, hook them up and don't worry about it. The charger and alternator
performance won't be negatively impacted by them.
Now when battery banks get large and solar
arrays get big and electrical consumption
is large and maximum charging efficiency is desired and maximum expensive battery protection is rerquired the systems get very complex quickly.
Let the technical quagmire begin!