Regulating solar power
QI have recently installed a solar panel system on my narrowboat using two 100 watt panels connected to my 12 volt leisure batteries via a MPPT controller.
The wiring of the solar system is exactly as the diagram attached (without the battery charger but charging from the alternator) copied from a Back Cabin item in the CB issue dated February 2017.
My query is: does the regulator on my alternator (I have a single 55amp alternator) fed to the two battery banks (leisure and engine) via a split charge diode have any conflict with solar system, or should there be a switch incorporated within the solar system to isolate any solar battery charging when the engine is running? If required, which side of the MPPT panel should any switch be positioned, i.e. input or output side of the MPPT panel? SIMON GARDNER
ATONY REPLIES: The controller must never be isolated from the battery when the panels are connected. Otherwise it could well set itself to the wrong voltage (24 volts in this case) and then damage the batteries when reconnected. This means any switch MUST go between panels and controller.
The solar controller and alternator regulator should work together with no issues except in a few cases when the solar controller manages to try an equalisation charge or if it’s set to a higher voltage than the alternator. In those circumstances and with very well charged batteries the alternator controller MIGHT shut down but with such well-charged batteries it’s of little consequence apart from the charge warning lamp glowing and the warning buzzer sounding. No damage will be done.
If your split charge diode is a passive device (not electronic) with just three thick wires connecting to it then it will be wasting half a volt or more of charging voltage. With solar charging I would advise getting rid of such old technology and fitting a properly wired Voltage Sensitive Relay instead. Then when you leave the boat away from shore power the solar will charge both battery banks rather than just the domestic bank. Email me if you want wiring details.