I am trying to set up a small 20W panel, I also need to connect outboard charger (5A), and smart mains charger. All plugged in turn into an external connection on the cockpit coaming. Have Phocos 4A rated controller, which states that it has a current draw of 4 mA. Connecting the battery to the controller with open circuit on the panel side, seemed to indicate that this draw was all the time.

As I only will use the boat+solar occasionally, I decided to use a plug system to disconnect the battery from the controller, and connect directly to the external deck socket. This should also prevent overloading the controller when using the o/b charger. To save further messing with plugs, I connected the solar input in parallel with the incomer. The theory being that an input voltage with an open circuit output shuld be OK for the controller.

With the battery thus connected to the input side, and no other connection, there is a voltage of circa 2V on the output of the controller. Conversely, with the battery connected to the output side of the controller, there is a voltage of 5.5V on the panel side. (Open circuit). This puzzles me, I thought it would have a diode to stop power loss through the panel.

Last but not least, I have blown three 10A fuses on the battery connection, for no apparent reason. The only current path that could do this that I can think of, is through the controller. All the other circuits test fine.

Any ideas?