Ok, this is the challenge. My boat came with a battery charger
that after all these years still works fine.
When I run the frig at the dock
, the power demand is 8amps or 80% of the max my charger
supplies. As a result, after a while the charger gets hot, and trips out. Aside from that the charger still works fine. So replacing it with a new one is a waste of money
With that as a starting point, how would you wire shore power
to a 12VDC AB unit that draws about 8+ amps?
One starts with a 120VAC > 12VDC 20AMP rectifier. If you connect the rectifier and the normal DC feed to the cooling
unit, when the rectifier is feeding the unit, it will back-feed to the batteries, and overcharge them. Likewise when on DC, the DC would back-feed the rectifier. I believe the result is the rectifier acting as an inverter
and back-feeding the AC circuit or at the least it would not be good for the rectifier's circuitry.
My thinking was to add diodes to both the rectifier and the DC cables
to prevent back-feeds.
I would like to keep the rectifier feed isolated from the boat's DC system. By switching or protecting both the pos and neg, I get 100% isolation. Am I overthinking that part?
The other option is a PURE two pole a/b switch. Unfortunately, I cannot find one.
Using a battery
switch allows for both A&B to be selected, this would result in fried batteries. Not an acceptable outcome. They also only switch the pos.