Charging and batteries

About a week ago I decided that before I installed the tracker and really invested time into it, I would try a couple of ideas. This involved two related items, more battery capacity and swapping out the repaired panel for the never broken one.

On Saturday I got the necessary connectors to enable me to use the two relatively new 9Ahr batteries that were in a UPS that has a failed controller board. I connected them in parallel with the existing 18Ahr battery, bringing the capacity to 36Ahr. I also swapped out the panels. As the main controller was inside on the bench at the time, I don't know what this meant to the charge state.

On Sunday I took the main controller and reinstalled it on the dock, reprogrammed the postcaps and did some miscellaneous repairs. Sunday night I turned the lights on at around 1930, with the intention of leaving them on to run the battery out. At 2300 they spontaneously turned off, it turns out that I had an entry in my crontab left over from previous efforts, so I turned them back on. They were still on when I went to bed about an hour later and they were off in the morning. I was unable the see the "bounce" on the battery voltage that would indicate when the controller cut the power.

However, this morning I collected this graph of the last 18-20hours.

From the left, on Monday, at about 1400, the panel voltage spiked up to ~19v, this is pretty close to the open circuit voltage, so it would appear that the charger took the load off the panel indicating the battery was fully charged. There is about 100mA of constant drain on the dock even with the lights off so the battery doesn't remain full for too long, you can see when the charge controller put the battery back on charge as panel voltage drops with the load to top the battery off. There are a few cycles of this until about 1500 at which point the sun is approximately 80° off axis. Here the panel is only getting very oblique sunlight and then around 1600, the sun is > 90° off axis and the panel is no longer producing anything of significance. Here the battery voltage starts to drop from the float charge level to the generally accepted 13.5v fully charged state.

Around 1830 the green line drops right off at sunset. The lights are on at this point until 2300. As you can see there is barely a drop in battery voltage during this time, or during the overnight hours. Around 0630 the sun came up, the panel started to produce electricity and the charging process was started Around 0930 the panel went open circuit again, so it's apparently fully charged already!

Morals of the story...

  1. If your panel is cracked and it's the only one in the array, don't try to repair it, just use the good one the seller sent to replace it.
  2. Make sure you have _plenty_ of battery, they really don't like being used close to their Ahr ratings. I was using 100% of a 20Ahr battery, but it appears I am using very little from the 38Ahr battery.