Re: Starting Batteries
It's not that a wet cell battery won't work for the starting system but you want to get the most life you can out of them. The rule of thumb is to never bank different type batteries together. This also can refer to the age of same makes and models of batteries (don't put an old battery with a new one). My issue is when the solar causes the separator to combine the batteries; bank A wants one voltage and bank B needs a different voltage. One bank will loose out and either be overcharge or under charged. Is it really that bad of a thing? Not really, but it does affect the life of the batteries. How many of us have killed our batteries by leaving the lights on by accident? We usually charge it up and go on our way but the battery has been damaged. Same with the alternator and what it puts out but in most cases an alternator doesn't fully charge an AGM battery. Twin 4D batteries are an expensive investment and trumps the starting battery system. Solar controllers usually have a setting for types of batteries and mine is set to AGM for that reason. It keeps the AGM starting battery up to par but can over charge the starter battery system.
In a perfect world I'd have a standalone solar panel to charge the starting system and a larger solar array to take care of the house system and would never let the two systems combine unless I needed a jump.
Separators (in most cases) allow the vehicle's on board charger and solar to charge both systems. Like my solar controller my inverter/charger is set to AGM. Again, the starting batteries can be overcharged.
Isolators allow the alternator to charge both battery systems only when the engine is running so it's not an issue with older vehicles that have those. Solar hooked to the house battery system doesn't charge (or over charge) the starting battery or batteries if an isolator is in the loop. It's an advantage to using isolators over separators in some cases. But because separators do charge the starting system AND house system, you don't end up with dead starting batteries which seems to be an issue with vehicles that sit for long periods of time between drives. If AGM's are used for starting and house systems, they like similar charging characteristics which is a good thing if both systems are being charged together as a single system.
There are so many variables that it's hard to nail down any perfect method. With 270 watts of solar (even with a smart solar controller) I was having issues. YMMV.
2006 Ford 6.0PSD EB-50/E-PH SMB 4X4 Rock Crawler Trailer
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