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Old 05-03-2019, 07:12 AM   #1
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Fridge a/c or a/c-d/c

I need to replace the fridge in a boat that is equipped with a gen set and inverter. An ac only fridge is much cheaper than a duel voltage one. I canít think of a situation when I would need to run on dc seeing that I would always have ac available either via shore power, gen set, or batteries via the inverter. Most boats seem to have multi voltage refrigerators so what am I missing..I assume that most would not spend the xtra money without a reason. Thanks cliff
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Old 05-03-2019, 07:16 AM   #2
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Greetings,
Mr. cb. All depends on how much you plan on being away from shore power, how big your battery bank and inverter are and how long you can stand your generator running.
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Old 05-03-2019, 07:31 AM   #3
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I guess this is part of my confusion. The inverter is using the same set of batteries from which I would be sourcing the 12 volt power. Is using 12 volt directly more efficient than converting those same 12 volts to 120 ac via the inverter??
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Old 05-03-2019, 07:43 AM   #4
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Doubt you will find an off the shelf boat / RV refrigerator as efficient as some of the high efficiency apartment refrigerators. Here is the route I took:

My New Apartment Refrigerator

Ted
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Old 05-03-2019, 07:52 AM   #5
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I guess this is part of my confusion. The inverter is using the same set of batteries from which I would be sourcing the 12 volt power. Is using 12 volt directly more efficient than converting those same 12 volts to 120 ac via the inverter??
Yes, direct 12 volt more efficient by about 20% dependent upon your inverter, refrigerator and method of calculation. I often shut my inverter off at night to reduce battery drain due to incipient loads from inverter, tv, sound equipment etc. The 12 volt decrease is about 6 - 8 amps. Not a lot but it all adds up when away from dock for awhile.

If you run your genset more than say two hours per day and have a decent sized house bank and charger, then a 110 volt unit only may well be the way to go. Go back to RTF's post #2, it all depends.
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Old 05-03-2019, 08:38 AM   #6
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We replaced our marine fridge 15 years ago with an apartment size AC fridge. Been working fine ever since, runs off the inverter when we unplug from shore power.
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Old 05-03-2019, 09:14 AM   #7
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One problem with running an AC on the inverter is the inverter. A refer will cycle on and off, should be on less than half the time. However the inverter has to be on all the time, in case the refer starts. Many inverters (Magnums, Freedoms, etc.) are very inefficient at idle, burning several amps doing nothing at all. That can double your battery draw.
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Old 05-03-2019, 09:44 AM   #8
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If you can find an AC only unit that will fit, I see nothing wrong with that route.
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Old 05-03-2019, 11:53 AM   #9
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I use a household AC fridge with good results. Much less expensive to buy. It runs on either shore, gennie or inverter. Most of the inverter time is with main engine on and gennie off, so efficiency there is of little concern. When anchored at night, it does put a hurting on my smallish house batt bank, but we are ok with that. Most nights I shut off the gennie to sleep unless super muggy or super cold.

Nice thing is if it poops, I can get a direct replacement from a home store, in stock.
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Old 05-03-2019, 01:12 PM   #10
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Doubt you will find an off the shelf boat / RV refrigerator as efficient as some of the high efficiency apartment refrigerators. Here is the route I took:

My New Apartment Refrigerator

Ted
I also went with a Summit apartment fridge; they have a huge selection of sizes, bought online with no hassle and free delivery. It seems very efficient, barely draws the house bank down overnight. And important to us, the freezer really freezes. Friends had a 12v fridge/freezer, and I would say the freezer just barely qualified as a very cold fridge. Maybe that was just their particular model, but we donít spend weeks on the hook, so I saw no reason to think about going that way.
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Old 05-03-2019, 01:14 PM   #11
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Quote:
Originally Posted by O C Diver View Post
Doubt you will find an off the shelf boat / RV refrigerator as efficient as some of the high efficiency apartment refrigerators. Here is the route I took:

My New Apartment Refrigerator

Ted
We are in the process of doing the exact same thing. After 3 Norcold replacements in 4 years, that run almost non-stop, Iím done with the expensive ďMarineĒ fridge.
We are putting in the same fridge that Ted used. And will run it off the inverter.
3 more cubic ft of refrigerator and some woodwork to make it fit, but in the long run I think we will use less power. And the summit fridge is about half the cost of another Norcold.
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Old 05-03-2019, 03:32 PM   #12
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Well, I think I know what I am going to do...ac only unit...thank you all for your input. Cliff
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Old 05-03-2019, 03:39 PM   #13
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If it helps...

I prefer AC/DC models. I can run on DC straight from the battery bank (charged by alternator, underway if the genset isn't on), no inversion loss... or I can choose to run on AC from either shorepower or genset... so our inverter isn't even connected to the fridge breakers.

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Old 05-03-2019, 03:48 PM   #14
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Second thought, I sprung for $75 (if memory serves) for Summit’s optional door latches. They work OK, but I can’t get them adjusted to self-close when the door closes. If I had to do it again, I’d spend 5 bucks on some arrangement with eye hooks and 4 dabs of 5200 instead.
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Old 05-04-2019, 08:55 AM   #15
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The better DC units that use an intelligent inverter to create pulsing DC will use loads less electric , a concern if the house batts are small.

75 AH per day rather than 100+ of other systems.

Some are even voltage sensing and will lower the internal box temperature when it senses charge power available.

The operators choice of on engine underway , noisemaker on, or power pole will help decide.
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Old 05-04-2019, 12:15 PM   #16
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I use a house size, double door reefer and 2 freezers. With the current inverter/battery setup, I rarely run a generator more than an hour a day. I time generator use with making water and laundry.
Cruising a dedicated alternator keeps the inverter banks topped off.
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Old 05-04-2019, 01:19 PM   #17
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So your inverter runs at about 88-90% efficiency, so yes, there is a 10% loss there. However if you take time to source an A+++ high efficiency domestic fridge, likely running with a digital inverter motor, then you'll find it much more efficient than marine units. Those Danfoss units do not compare. The only fridge more efficient is a Sunfrost, but you'll blow $2500 for one of those.
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Old 05-04-2019, 02:40 PM   #18
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We have a 19cuft domestic fridge. We shut down the genny at night, during shore excursions and meal periods. If you keep the freezer loaded with ice and other provisions it holds temperatures well over 10 hours without power as long as you keep doors shut. Works well for us.
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Old 05-04-2019, 07:24 PM   #19
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The most power hungy appliance on your boat will be your refrigerator, no matter whether it is AC, AC/DC or DC.

Since you are in Florida, you probably have Air Conditioning (another AC), so you also more likely than not, stay close to a source of AC, whether from your own generator or shore power. You should get a household style, energy efficient AC fridge.
You will likely be able to keep your energy usage down to about double what the DC fridge would use, but as you can't stay away from a source of AC power anyway, that won't matter.
If you were in Washington or BC, you would be far better off with DC only.
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Old 05-04-2019, 08:39 PM   #20
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Cliff,
Your inverter/battery bank sizing will impact how the 120v refrigerator works for you. Our boat is a 120v boat, with some 12v and some 220v services. The inverter(2) and battery bank are online 100% of the time. Our refrigerator is a LG household freezer bottom, French door unit. At night we turn on the energy saving button and doing so, drops the draw to around 15 amps. It has two ice makers that can pull a little bit more.
I put two 12v muffin fans behind the refrigerator to push the heat from behind the unit.
If we anchor, we need to run the genset for 2-3 hours once a day. If we run the engines during the day, we do not need to run the genset as the alternators keep the batteries happy.
Good luck.
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