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05-03-2019, 07:12 AM
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#1
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Senior Member
City: englewood florida
Join Date: Apr 2019
Posts: 168
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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 can’t 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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05-03-2019, 07:16 AM
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#2
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Enigma
City: Slicker?
Join Date: Oct 2007
Posts: 16,567
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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.
__________________
RTF
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05-03-2019, 07:31 AM
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#3
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Senior Member
City: englewood florida
Join Date: Apr 2019
Posts: 168
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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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05-03-2019, 07:43 AM
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#4
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Guru
City: Fort Myers, FL... Summers in the Great Lakes
Vessel Name: Slow Hand
Vessel Model: Cherubini Independence 45
Join Date: Dec 2010
Posts: 12,835
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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
__________________
Blog: mvslowhand.com
I'm tired of fast moves, I've got a slow groove, on my mind.....
I want to spend some time, Not come and go in a heated rush.....
"Slow Hand" by The Pointer Sisters
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05-03-2019, 07:52 AM
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#5
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Guru
City: Carefree, Arizona
Vessel Name: sunchaser V
Vessel Model: DeFever 48 (sold)
Join Date: Apr 2008
Posts: 10,188
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Quote:
Originally Posted by cbouch
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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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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05-03-2019, 08:38 AM
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#6
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Senior Member
City: Cape Coral FL\Grand Island NY
Vessel Name: Missy
Vessel Model: 1997 Mainship 350
Join Date: Jun 2013
Posts: 192
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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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05-03-2019, 09:14 AM
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#7
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Guru
City: San Francisco
Join Date: Apr 2018
Posts: 3,094
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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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05-03-2019, 09:44 AM
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#8
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Moderator Emeritus
City: Au Gres, MI
Vessel Name: Black Dog
Vessel Model: Formula 41PC
Join Date: Jul 2015
Posts: 21,191
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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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05-03-2019, 11:53 AM
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#9
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Technical Guru
City: Wilmington, NC
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 6,194
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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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05-03-2019, 01:12 PM
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#10
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Senior Member
City: punta gorda, FL
Vessel Name: Blue Bayou
Vessel Model: Hatteras 43MY
Join Date: Jun 2016
Posts: 149
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Quote:
Originally Posted by O C Diver
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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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 don’t spend weeks on the hook, so I saw no reason to think about going that way.
__________________
Punta Gorda, FL
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05-03-2019, 01:14 PM
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#11
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Guru
City: Pahrump, NV
Vessel Name: Pairadice
Vessel Model: Sold Selene 47
Join Date: Jul 2014
Posts: 1,967
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Quote:
Originally Posted by O C Diver
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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We are in the process of doing the exact same thing. After 3 Norcold replacements in 4 years, that run almost non-stop, I’m done with the expensive “Marine” 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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05-03-2019, 03:32 PM
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#12
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Senior Member
City: englewood florida
Join Date: Apr 2019
Posts: 168
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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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05-03-2019, 03:39 PM
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#13
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Guru
City: Annapolis
Vessel Name: Ranger
Vessel Model: 58' Sedan Bridge
Join Date: Aug 2013
Posts: 7,088
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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.
-Chris
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Chesapeake Bay, USA
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05-03-2019, 03:48 PM
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#14
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Senior Member
City: punta gorda, FL
Vessel Name: Blue Bayou
Vessel Model: Hatteras 43MY
Join Date: Jun 2016
Posts: 149
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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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Punta Gorda, FL
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05-04-2019, 08:55 AM
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#15
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Guru
Join Date: Oct 2007
Posts: 22,553
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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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05-04-2019, 12:15 PM
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#16
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Guru
City: Between Oregon and Alaska
Vessel Name: Charlie Harper
Vessel Model: Wheeler Shipyard 83'
Join Date: Jun 2016
Posts: 3,023
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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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05-04-2019, 01:19 PM
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#17
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Guru
City: Seattle
Join Date: Jun 2012
Posts: 3,312
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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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05-04-2019, 02:40 PM
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#18
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Senior Member
City: New Rochelle, NY
Vessel Name: Jerry Land
Vessel Model: Grand Banks/Alaskan
Join Date: Aug 2015
Posts: 253
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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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05-04-2019, 07:24 PM
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#19
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TF Site Team
City: Saltspring Island
Vessel Name: Retreat
Vessel Model: C&L 44
Join Date: Nov 2007
Posts: 5,663
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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.
__________________
Keith
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05-04-2019, 08:39 PM
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#20
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Senior Member
City: North Port, FL
Vessel Name: Seven Tenths (sold)
Vessel Model: Mirage / Great Harbour 47
Join Date: Dec 2012
Posts: 477
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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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