Refrigerator dc power

[Ricksearay]

My 1992 Searay Sundancer refrig seems to be powered by both batteries. When I select battery1 or battery 2 on the battery select switch both batteries are powering the refrig. I would have thought that the boat would have been wired so that the the refrig would be powered by just one of the two batteries. I would like to reserve one battery for the engine starter. Any comments ?

also, How long would the refrig last powered by a 600cca battery with the refrig requiring 5 amps. I seems to run on a 3-% duty cycle. I.e the compressor is on for 1/3 of the time

 

[km1125]

The CCA of a battery doesn't tell you its capacity. You need the AH value. Roughly, for a group 24 it's 70, a group 27 it's 85, for a group 29 it's 100 and for a group 31 it's 110. Those are just rough numbers. You don't want to use more than 50% typically on a lead-acid battery. So if your fridge draws 5 amps and runs 3x% of the time (less assume 33%, but on hot days it might be more like 50%), then each hour it's averaging jus under 2AH. So a Group 31 battery would run it about 24 hours (24x2=48AH and you shouldn't use more than 55AH on the battery)

Does your fridge run on AC? Many boat fridges do and only use DC when the AC is not available.