Ask PYS: Power

DC Only Fridge, on Oct 13, 2016 asked:

Thank you again for the audit and the install. I am delighted so far. The installer was very professional and seems to have got everything set up properly. As you know the battery monitor is great fun. I've been obsessively testing all my devices to see what load they put on my system. I have a question. My fridge will only work off my battery. How much damage am I doing to my house batteries if I leave it on all the time while connected to shore power with the batteries charging? The battery monitor says the fridge draws about 2.5 amps and 30 watts at the setting I would use. One obvious risk is if I lose power I would drain my house batteries. But if I eliminate that risk by checking in every few days will I be causing unreasonable wear on my batteries?

You are right, once installed a battery monitor gives a boat owner lots of insight into how amp each load draws on their battery bank.  The dilemma about how to operate a DC only powered fridge is a common one. I too have the same set-up on my own boat. When connected to shorepower your battery charger will offset the load from the fridge by continuously topping off the battery.

The problem with this setup is that if you ever lose shore-power, while away from the boat, the fridge will run off the batteries for a while and will eventually run them completely down, and then the batteries will be empty and not charging until the AC power is restored. For me it's a risk I take. There are certain solutions to this: A) get an AC/DC powered fridge B) Run the fridge off a relay that de-energizes the circuit once the voltage reaches 12 VDC or something similar.  -Jeff