Drop in voltage with constant current
The usual process is for the voltage to rise with a constant current hence the idea that when a battery is highly or fully charged the voltage is regulated.
But I have found that although the voltage is regulated at 15.63 the current feeding 3 x 120Ah batteries has gone from 11.2A to 13.4 over 80 minutes. This could be problem with the Victron Direct readings but I have had the same problem with a single 120Ah battery on a traditional mains charger. In this case the current ranges from 8 to 2 for periods of many hours.
I have this idea that the batteries are sulfated and as such provide a high resistance to charge and hence a high voltage is needed for it to absorb wattage. But after prolonged periods it is if a layer of sulfate is broken down and the resistance drops leading to a higher current. This seems to be happing multiple times over the last few weeks where I have been trying to recover capacity in what in all accounts are heavily sulfated batteries. By heavily I mean a first test that showed 10% capacity and a second that showed 25%. Since then I have had single batteries charged either for 1, 2 or thee days continuously by a mains charger that can produce 12A, or any number up to three in parallel fed by 15A at up to 15.94V for whatever sun is available. The max so far has been 1.25Kw in one day. This has been going on for some two weeks and the anomaly is still here.
**13:30** Just spoken to Phil at Bardens Uk who has confirmed that the dropping voltage is the sulfate being broken down.
Created by • Last edit by on 07 Feb 2018