Originally Posted by Ed-Sommers
You are on the right track although I would consider wiring the panels straight series for a 48 volt configuration, that will make the 20 Amp MPPT controller run more efficiently.
Not exactly correct. Higher voltage will enable use of lighter gauge wire or longer wire runs from the panels to the controller but this is not what limits the controller's ability to charge the batteries. Wiring in series may exceed the max Voc of the controller and it also greatly reduced panel output if one of the panels is shaded at all. Three 17.7v panels in series would be more than my Blue Sky 3024 MPPT 30 amp controller can handle as it tops out at 45.6V.
Before your wire up your panels and damage your controller check with the tech support people for confirmation of your setup. It is not what you know but what you know that is not so that can get you into trouble.
The MPPT charge controller is going to use the heat sensor to adjust charge voltage so as not to overheat the batteries and so generate more outgassing with flooded type batteries like the Trojans you bought and shorten their life. The controller is going to charge at a low voltage if it is set for charging lead acid batteries as compared to AGM type.
You may get 5 amps per solar panel but only for a limited number of hours per day which is what in total determines how much the controller can provide in the way of charge to the batteries. If you have 200 AH at 12v with the 4 Trojan batteries and discharge them 50% overnight then your charging setup if it is all that is used (excluding charging from the alternator for example) needs to replace 100 AH of charge during the hours of sunlight.
Once your system is in place and assuming you have a monitoring device like the Tri-metric you will know how much charge is being taken from the batteries and how effective your panels are in replacing that charge. You can also accurately assess your RV's baseline power demand.