Boat Electrical Problem

by Chuck

When on shore power or using the genset my batteries are drained running the frig/freezer 12 VDC motor for belt driven compressor. It is a Grunert system converted to all DC from batteries or alternator. The fridge is about 4 cu feet, the freezer about 5 cu feet. or maybe vice versa. So I bought an 80 Amp AC to DC converter. Yesterday I disconnected the red cable connection at the battery leading to the DC distribution panel and switched off the charger. Then connected that cable to the Red + on the converter and the Black - to the Battery minus post. Then switched on the refrigeration CB as usual. It worked great. The entire boat's DC load was powered by the AC to DC converter. And the Refrigeration system worked super without draining the batteries!!!! yea!!

Now I am trying to figure our how in the Sam H to make it so all I do is flip a set of switches to power the distribution panel with either the batteries or the AC to DC converter.

First an AC set of CB's for controlling AC to the Charger or the Converter. Easy, a set of AC CB's with a device that allows only one or the other.

Second, I imagined a DC switch that would either connect the distribution panel to the battery or the converter. These are big wires so not really sure what type of device to use that would allow the AC CB's and this switch to act as a pair. i.e. when the converter AC is on then the switch must be positioned to disconnect the battery from the distribution panel and connect the output of the converter to the panel. This is where I am stuck! Anyone know the solution? Thanks.