Harald, I have never used that particular controller, but as no one else has chimed in I will add my 2c worth.
Most of these types of problems are due to high resistance in one of the connections. Check the voltage drop over both the positive and negative cables
, measuring from the solar panels
to the input on the controller and then from the output of the controller to the battery bank. This needs to be done while the solar panels
are producing significant power. A quick and crude, but often effective technique for high current
devices is to feel the temperature at each of the connections. It will be warm if there is significant resistance.
While the above is certainly worth checking, your symptoms are not typical of this type of fault. I suspect your controller is simply defective. Unfortunately, MPPT
controllers are not the most reliable of electronic devices, and the failure rate is reasonably high. It is possible your unit is simply overheating
when the solar panels
are putting out a higher current. Solar controllers need plenty of ventilation. As a test try mounting a temporary fan blowing over the controller and see if that fixes the problem. This will also show if the internal fan (if one is fitted to this controller) has stopped functioning.
If not, you can test if the solar controller is defective by simply bypassing the connections and wiring
the panels directly to the batteries
. As you have low voltage "12 v" solar panels the output should be close to same output achieved when the controller was working normally. If you do decide to do this you need to keep a careful eye on the battery voltage. If you let this climb significantly above the normal absorption voltage, your batteries
and even other electronics
could be permanently damaged.
Finally, you can disconnect and test the solar panels individually looking at the maximum voltage and then the maximum current each panel can produce.
These tests should narrow down the defective component.