So I've been noticing for a long time that my batteries seem to drain down at night. This was a minor annoyance previously, but now that there are only around 10 hours of sunlight in the day (sunrise ~7AM / sunset ~5PM), it has become a real issue as the batteries are now hovering around 20V and barely get above 22 after a full day's charge.
Now, the charge controller is supposed to have a night disconnect that prevents nighttime discharging through the solar panel. I had assumed that this was controlled by one of the potentiometers on the inside. So last week, I broke out the manual and went over all the details and found that they really only control how high it takes the voltage before it stops charging. They do not impact the low voltage disconnect. I did make a few adjustments to have it try to give more charge to the batteries. This seemed to have no affect.
So I emailed the Xantrex support people. They gave me a few troubleshooting tips, one of which is to determine if the batteries themselves are holding a charge. To test this, I would charge the batteries to full capacity (which at this point may involve taking them home), disconnecting the load and charge controller, and see if the voltage drops over a 12 hour period. If I had one, I could also try a DC clamp on ammeter to see if current is flowing to the solar panels.
I currently have no easy way to disconnect the solar panels. I have ordered two DC circuit breakers - 1 50A one for between the solar panels and the charge controller and one 100A for between the batteries and the load. Each breaker is around $25 so I will be adding $50 once I set these up.
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