Originally Posted by Ironhinge
Although it sounds like it is unnecessary from your experience, if someone with a setup like yours wished, they could protect the battery from overcharge during long-term storage by disconnecting the 4a from the simplex.
When you disconnect the AC power or turn off the Samlex battery charging stops so you don't have to disconnect the battery from the system. Also, a flooded lead-acid battery will not overcharge if the charge voltage is kept at 13.8V. The current supplied will be just enough to offset the natural self-discharge of the battery. Of course is is a good idea to disconnect the battery if the trailer will be in long-term storage. And make sure the battery top is clean. Sulfuric acid is conductive and even a thin layer on the battery top will allow the battery to self-discharge quicker. If the camper will be stored for more than three months try to arrange to charge the battery during storage.
Regarding intelligent, smart or three-stage chargers - They charge a battery in three steps, bulk, absorption and float.
In bulk charge the charge is current limited, usually at C=0.1 to C=0.5 with C being the battery capacity. This is also called a fast charge mode where a completely discharged battery is brought back to almost full charge (about 80%) in 2 to 6 hours.The problem is heat, the enemy of all things electrical
or electronic. You are limited by I squared R with the R being the internal resistance of the battery. Heat dissipated goes up as the square of the charging current and, if not controlled, can literally cause the battery to melt down. The internal resistance of the battery also tends to increase as the charge rate increases so the problem is compounded. High charge rates can also cause the lead plates to disintegrate due to gas bubbles forming in enclosed areas in the plates.
In the absorption step the charge is voltage limited (usually at about 13.6 to 13.8V). This brings the battery up to full charge (from 80% to 100%) slowly but is more efficient overall as the charge current is much lower (lower I = less internal heating of the battery).
The final step is float mode where the battery no longer accepts a charge. It is full, satisfied and happy. This is the point where current flow to the battery is just enough to offset the self-discharge rate of the battery. Some chargers detect when the charge current drops below a threshold and then lowers the voltage a couple of tenths of a volt.
The Samlex really only uses the absorption and float mode since the initial charge rate is well below 0.1C (for a 100AH battery). Although it takes longer to charge a fully discharged battery this way it is much easier on the battery since there is less heating per unit time and more time to dissipate the heat. A cool battery is a happy battery!
There is another charging mode called equalizing where the battery is hit with a higher voltage per cell and a much higher current. This mode is normally only used with large stationary battery banks such as telephone switchboard cells. The charge is held until the cells are liberally gassing to ensure that all cells in the system are at 100%. Although I have heard of people using this mode on batteries in RVs I do not believe it is a good idea for the relatively small batteries we use. In addition to the heat generated there is the danger of exploding hydrogen gas. Just a little spark and you have battery pieces and sulfuric acid flying everywhere.
Some smart chargers use sensing circuitry to determine when to switch from bulk to absorption to float modes. Since the Samlex doesn't use the battery slaying bulk charge mode it isn't necessary.
The only downside of this system is that it takes longer to recharge a completely discharged battery. But you wouldn't let your battery get completely discharged would you?
Sorry to be so verbose but the above dissertation only scratches the surface of battery charging science. Whole books have been written on the subject.
73 for now