When I was in Haiti, I saw how important the lead acid battery bank was to their lives. At Ecole Shalom, they had just been connected to the grid the preceeding May. (I was first there in November). During the time I was there, the power went off during the afternoon or evening on most days. It was clear that many of the teachers didn’t have power at home, as they were always plugging in their chargers and phones during the school day.
When I arrived, I discovered that four of the eight batteries used to provide power to the 110V circuits were not functioning. By looking at the specific gravity in each cell, I noticed that one of the batteries had a very low charge level. Later, as I was doing a cleaning operation on all of the copper cables that connected the batteries to one another, I noticed that on the battery that had the low charge, there had been a transfer of metal from one side of the connector to the mating half. This usually happens where there is enough sparking and heat generated to melt the copper. I guessed that the nuts holding that particular cable to the battery had not been tightened properly, that the heat generated had boiled the acid out of the battery. The water had been replaced, but the sulfate was trapped on the plates, and the battery was dead. We replaced the battery, and the system worked much better, even though the experts on the web suggested that it wouldn’t work very well to put a new battery into an already existing array.
The inverter, shown in the picture on the table, is able to display a number (0-100) which the manual says is the percentage of remaining charge. Everyone was confused when that number became 100% after the power came back on. I tried, it seemed to me unsuccessfully, to explain that the machine was actually measuring the voltage of the batteries, and using a well known translation table and relationship between voltage during discharge, and remaining stored charge. That relationship does not exist during the charging phase.
As an experiment, I purchased a battery monitor from Xantrex, which monitors the current from the battery, and displays the degree of charge or discharge expressed as a percentage. This battery monitor turned out to be much more useful, and believable, then the display on the battery charger had been, because it was consistent whether the battery was on its discharge or charge cycle. It would also keep track of the actual current out of and into the battery, and show changes in the system’s health over time.
I also had the feeling that there was little awareness of the need to use the equalizing feature of the battery charger (which is initiated by putting a paper clip into a small hole on the control panel of the charger). This equalizing process applies an extra large charging voltage which causes gassing and mixing of the electrolyte, and dislodges the sulfate crystals which coat the surface and lead to early battery failure.
As a techie and an engineer, I kept wanting to provide more visibility into the health of the battery system and make the removal of the sulfate crystals more automatic.