wa8yxm wrote:
pnichols wrote:
For years, now, NO ONE has explained the technical reason(s) as to why RV deep cycle dry (AGM) lead acid batteries require voltages greater than 14 volts to charge them fully if one has plenty of time to do less-than-14-volts charging. Is there some electro-chemistry reason - maybe related to activation energies, for instance?
Actually it has been explained many times and it is very simple.
To use a classical reference (Pushing a rock up a hill) for this discussion the "Effective weight" of the rock is what you would see if you put a scale against the rock perpendicular to the hill. IT will of course be a fraction of the actual weight of the rock but this is how hard the rock pushes back against you.
Now if the Effective weight is 13,600 pounds (13.6 thousand pounds) and you push against it with 13.6 Thousand pounds you are going no place fast. the rock will not move.
To move it up the hill you need to PUSH HARDER. perhaps 14,600 pounds will roll it up the grade.
Same with charging a battery. push 13.6 and you go nowhere. that's why it is called FLOAT. .To push amp hours into the battery YOU HAVE TO PUSH HARDER. That's all there is to it.
That's a rockhound answer, but not a technical one. :)
It still merely argues for faster charging through use of a higher charging voltage ... not supporting an argument for damaging charging through use of lower voltages that are sill higher than intrinsic battery terminal voltages throughout the charging process. Of course a higher charging voltage will force more current per hour through any given resistance -> EE101.
But if one has the "hours to work with" - like after an RV trip when the rig is parked back home plugged in for weeks - how can deep cycle AGM batteries be ruined by a stock converter taking a longer time to charge them fully?
I wonder how many $$$ have been spent by RV AGM battery owners replacing their "stock converters" because their converters would in no way properly treat their AGM batteries? With motorhome RV'ers who camp only a few days here and there on trips and have an alternator dumping amps into their coach's AGM batteries between camping spots, why must 13.6-13.8 volt fixed voltage converters be replaced ... other than for faster charging desired when drycamped using a generator for charging?
Of course liquid acid RV batteries present another situation. They sometimes need stirring via high charging voltages and can also have their acid boiled away via being left on fixed voltage converters putting out a too-high fixed voltage.
