I'm currently using a MPPT 100/15 with a 12V battery bank (2 x 12V 100Ah Lead Acid batteries in parallel) with 2x100W solar panels. The solar controller's settings are on 14.4V absorption and 13.9V float. The equalization voltage was set to 16.2V but it is disabled and I've never manually triggered the equalization.
I also have a BlueSmart 12/15 charger which I set on power supply mode during the day with a voltage of 13.4V while the solar panels provide power to my system. It's charge mode's settings are similar to the solar charge controller (14.4V absorption, 13.8V float and 13.4V storage).
Earlier today I noticed a strange series of events.
1. The power from my solar panels dropped from around 130W to zero. (it's a sunny day, panels had no shade, I measured the panel voltages and everything seemed fine on the panels and at the cable going into the solar charge controller when unplugged - around 70-80V open circuit voltage). After this the Victron app stated that the charging state is "Off".
2. The reported voltage on the victron connect app showed that the voltage from my solar panels dropped from the normal 65-ish Volts to just above the battery voltage. This was thus different to what I measured with my multimeter at the cables going into the charge controller while they were unplugged.
3. I changed the BlueSmart charger from power supply mode to charger mode, detached the solar panels and measured their voltage (mentioned in point 1).
4. I re-attached the solar panels.
5. Soon thereafter I heard a boiling sound coming from the batteries and noticed the battery voltage going over 15V and steadily climbing.
6. I immediately switched off the BlueSmart charger, but it had no effect.
7. I then detached the solar panels which brought the voltage down again.
8. To investigate I tested this by leaving the BlueSmart charger switched off, and re-attached the solar panels. The voltage started climbing again.
Afterwards I took some screenshots (below). It's quite clear on the screenshots that the voltage climbed each time I re-attached the solar panels.
What I'm seeing is:
- The solar charge controller is in an "off" state.
- The charging current was showing zero
- The power and current from the solar panels were showing zero
- The battery voltage kept on climbing and I heard the Lead Acid batteries boiling.
- Even though an audible boiling sound came from the batteries, the solar power and current and battery charge current all showed zero.
What am I missing?
It almost seem like the battery voltage was chasing the solar voltage. I don't think this was an equalization happening because during "step 7" I did decrease the equalization voltage to 14.5V and the battery voltage still climbed past it to 16V+ before I detached the panels again.
Did my SmartSolar MPPT charge controller break? It's only a few months old now.
Did it perhaps somehow decide the batteries are 24? I double checked the settings and the battery is set to 12V. At no point in time was the battery cables disconnected.
I will be testing everything again in the morning when the sun is back up and if anything changes I will comment on this post.