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Old 01-30-2016, 02:01 PM   #1
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At the dock we use shore power. Often we are away for extended periods and leave our refer "on". We have the option on our electrical panel of running the fridge on AC or DC power. It seems that using DC would allow for a back up, albiet temporary if the AC were to fail. I have also heard that refers last longer if continually powered and they are best powered with DC. What do you think?

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Old 01-30-2016, 02:22 PM   #2
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I have the same option, and once had the same train of thought. Until I arrived at the boat late one Friday evening after having been away for a week or so, and found the batteries DEAD! The Inverter/Charger had faulted for some unknown reason and of course the fridge drained them down. Now... here's the kicker. Dead batteries don't power bilge pumps. Would you rather your fridge stay live for a few more hours or a day, or have your sump pumps functioning and maybe someone noticing or hearing the alarm?

I now leave mine on 120v shorepower. I'd rather risk throwing away a few condiments. BTW, I bought a small digital thermometer that records current, high and low temps. That way I know if the power was out and the fridge exceeded a certain temp... I'm tossing everything!

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Old 01-30-2016, 02:28 PM   #3
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Excellent point. Thank you.
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Old 01-30-2016, 02:43 PM   #4
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A small bag of ice cubes kept in the freezer will also serve as an alarm.
If the ice is melted or melted even a small bit then the power was out and the food should be suspect. Even if the fridge restarts, if the temp rose enough to start melting it will show.
Not my idea, just read it somewhere.
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Old 01-30-2016, 02:58 PM   #5
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I have never heard of the bag of ice tell tale. Good idea.

This topic was discussed extensively a few months ago. There are two ways to lose power at your dock: the marina doing maintenance where it should only be out for a day or less, or someone disconnects your shore power cord where it will be out a long time.

The DC power will probably carry you through the marina power outage, but not the shore power cord disconnect. And then you will have dead or almost dead batteries which might have to be replaced.

I would power the fridge with AC and keep the DC breaker off. Then look at the ice to tell if you have to throw away any food.

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Old 01-30-2016, 03:13 PM   #6
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When the AC power goes out I get a text.

Same thing if the charger fails
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Old 01-30-2016, 03:41 PM   #7
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My fridge will automatically run on AC if available and falls back to DC if the AC goes off. Depending on what model you have yours may too? I would be concerned running on only DC that if anything happened with shore power OR your charger you could come to the boat and find your house batteries run down.

As far as running on AC or DC being "better": Depending on how your fridge is designed, it may not matter at all. I know with many units (Mine included) there is ONE power supply that has both AC and DC inputs - only ONE output that runs the compressor. So the compressor doesn't know the difference.

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Old 01-30-2016, 04:11 PM   #8
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If you have ice trays, put a penny on top of one of the cubes in a tray.

If you come in and see the penny gone, or at the bottom of the tray, you know it melted and refroze. We used that when i was growing up with freezers.
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Old 01-30-2016, 06:16 PM   #9
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Not a good idea to have your bilge pumps on the same battery that has other ongoing loads when the boat is at rest.

"There's the Right Way, the Wrong Way, and what some guy says he's gotten away with"
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Old 01-31-2016, 08:16 AM   #10
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I leave mine running on DC, but have a low battery cutout, so it switches off at 12.2V.

I don't generally leave food in it when I'm away for an extended time, so at worst the beer gets warm. That's perhaps slightly less critical than the batteries not being able to operate the bilge pumps.
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Old 01-31-2016, 09:17 AM   #11
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I have an AC only fridge and freezer. I like it separate from DC mainly to not run down the batteries.
If AC goes off, the gen has an option to auto start on a load demand so it would go off and on by itself, but I wont use it, I don't like the idea of it starting when I am not around. The gen load demand feature does not sense the battery charger, otherwise it would run all the time. Power for the charger comes off the gen before the load sensing circuit, I made that modification. Bad enough that the fridge runs almost all the time.
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Old 01-31-2016, 09:34 AM   #12
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Not sure what you mean by leaving the boat for "extended periods" but for us we leave the fridge on 110 only for periods up to a week maximum and then empty it out if longer.

The only time we use it on 12volt is for extended anchoring overnights when 110 and inverter shut off. We drain house batteries much less this way with incipient 110 loads off.
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Old 01-31-2016, 10:30 AM   #13
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We hang on a mooring and anchor out while cruising nearly 100% of the time. If I take the boat to the dock for an overnigter for maintenance, I'll run the fridge off AC, as well as to fully charge the 3 battery banks (house, start, and thruster/windlass). On a 1-10 NovaCool thermostat, we keep the fridge between 3-4, enough to keep ice from melting. We have an 8 amp, 16.5 volt, 130 watt solar panel on pilot house roof, and that's enough to keep the house batteries charged while on the mooring or anchor. Unless we go through several days of no/low sun, we're usually OK. If we leave the boat for a couple of days, I'll turn thermostat down to "1", and that will defrost the freezer, but hold cold for when we return. NovaCool fridge has an 11.7 volt cutout. If we leave for an extended period, say 4 days or more, I'll turn off the fridge. When we return, I'll jump start the fridge (set at "6" or above) by either taking boat to dock, plug in, load up, wash down, etc., or just run engine (we have no generator) for an hour, or we just take off.

Just another perspective of refrigerator usage without shore power. At some point, I may add another solar panel, but this has served us for over 10 years. Maintaining a good set of house batteries is important. We have a pair of 6 volt Interstate house batteries. The original set lasted 10 years! I just replaced them with a pair of 232 AH 6 volt Interstate batteries last August 2015.
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Old 02-02-2016, 07:03 AM   #14
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Here in FL where lots of the population gets out of the heat for the summer season. leaving the fridge ON is the reccomrnded procedure.

AC power or DC power might make a difference in a power outage to the Contents of the fridge , but probably not its service life.

Although AC power can come with a power surge that might fry the fridge.

Here is one insurance policy,,

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Old 02-02-2016, 08:45 PM   #15
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Refer on AC only and nothing in it that can spoil and ruin the unit.

The boat doesn't leak so no need for the bilge pumps except the dehumidifier and it would not be running anyway if the power was off.

We only have mustard, ketchup ice, beverages and water in the refrigerator when not cruising.

Battery charger is off as the solar panels keep the batteries up, they have no load on them anyway.
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Old 02-03-2016, 12:31 AM   #16
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I think most refers that are 120AC or 12DC use only 12DC to run the compressor. They use 120AC when available but invert to 12DC for running the compressor.
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Old 02-03-2016, 12:52 AM   #17
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The Norcold AC/DC reefer/freezer was installed the year before we bought the boat in 1998. In the last 17-plus years it has never been off, and we keep it stocked with basic stuff year round. In the slip it runs on AC, when we're out we switch it to DC. However as CapTPT wrote, the compressor runs on DC. On groundpower the unit's inverter changes the AC to DC.

I like the penny idea.

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electrical, general, refer, refrigerator

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