Automated Power switch
Automated Power switch for using direct power 12V from power supply connected to shore and switch automatically to battery power.
Independent power supply helps to minimize additional load to battery charger. Usually chargers get confused from constant load applied to battery during charge cycle. Charger can't properly detect moment to switch to floating mode.
So, I installed independent PSU 14.5V - 40A to provide stable power and took load from battery charger.
Originally i "mixed" power using Dual ideal diode board - very simple solution - power sourse with higher voltage feeds loads on the boat. it all good up to moment when battery get fully charged. Then SOMETIMES (I caught that moment) power supply, battery charger, battery itself and ideal diode chip starting switching storm. It results short power drop on main 12V bus resulting computer to restart several times in 10 min.
Coming to power switch, instead of feeding boat from source which has higher voltage it implements kind of UPS logic. It feeds bus from PSU if it's output is above 12.5V and below 16V. If shore power is lost or power supply produce wrong voltage switch reconnects 12V bus to battery. Then when shore power returns it waits 10sec to make sure shore PSU power is stable and in the range, and only then switch loads to it.
Also switch disconnects all loads from battery if voltage drops below 9V on the battery side.
Design based on microcontroller and all timing and voltage ranges may be set in Firmware.
However I do not expect to use it at continuous currents >80A on batteru (breaker set on battery at 80A) and 40A on PSU (PSU limited internally)
Due to transistors Low Rds resistance (0.75mOhm) switch at 80A current will produce less than 5W heat and with 70x70 mm heat sink design should work ok.
Installed at the boat, Weekend sailing and coupe overnight works well.
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