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Old 10-28-2015, 02:35 PM   #21
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Right, uses a rectifier when a/c applied to produce 12 volts dc if it is a dc comp and an inverter if it is a 110 ac comp.
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Old 10-28-2015, 02:57 PM   #22
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Originally Posted by djmarchand View Post
Well, I have some experience and some data. Even Energy Star 110V refrigerator/freezers use about double the WATTS of a 12V system. I am using watts as the basis of comparison because it is volts time amps and is the right way to compare the energy use of different appliances with different voltage requirements.

A 6 cu ft Nova Kool refrig/freezer for example is rated to use 5.2 amps at 12V DC running. It will probably run 50% of the time in the tropics so it will require about 60 amp hours daily. Your 400 watts of solar will produce about 150 AHs daily in the tropics. Since refrigeration is the single biggest load for a full time cruiser you should certainly be ok.

But the same size refrigerator designed for 110V will use 2-3 times the equivalent amp hours or up to 120 daily if it is a non Energy Star rated unit which is what I suspect that you already have. As Ski notes above his small bar size refrigerator uses about 200 watts running which is three times the wattage of the larger Nova Kool DC fridge. Your solar will barely keep up with that and whether you get meaningful wind power depends on where you anchor. But if you have a generator then you will probably be ok if you just run it for a few hours on cloudy days to recharge your batteries.

So I think you may want to upgrade to a DC system, particularly if you don't have a generator. The best for power consumption is a well insulated box with a keel cooled Frigoboat system. That will be particularly efficient in the tropics. But it does require building a box and insulating it yourself because AFAIK the Frigoboat is only available to install in an existing ice box. An air cooled system like the Nova Kool referenced above will use about 20-30% more power due to less insulation and air cooling but should still stay within your DC production capability.

David
Many (most) full-size (>20 cu. ft.) household refrigerator/freezers with all the bells and whistles consume less than 1.5 kwh per day, nowadays, and plain-jane units get down to 1 kwh per day or even less. On an energy use per cu. ft. basis, this crushes the dc unit referenced above (700 wh per day for 6 cu. ft.).

I'm not sure "dc units, danfoss compressors, etc. are more efficient" is a given any more. I appreciate there are many variables (ambient temperature being a big one) that make precise comparison difficult.

But when you factor in purchase price, installation and repair costs, I'm starting to think household units may be the way to go, especially on cats where heeling is eliminated.
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Old 10-28-2015, 03:51 PM   #23
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Aren't we forgetting the cost of an inverter? 2500 watts (I don't have an inverter) is about $2000, which is another thing to worry about when operating a big fridge. Also, losing an inverter (or have two, like many do) would take out all your 110 V appliances, single point of failure? Also, frost-free on a boat? I am skeptical that a frost-free would be prudent on a boat, the moisture under the fridge would be a problem in rough water - where would it go?

The Danfoss does not shut off, it runs constantly but at variable speed to avoid the high current draw required to start an electric motor. I just bought a new Nova Kool fridge.
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Old 10-28-2015, 04:07 PM   #24
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I don't think you would buy an inverter solely to run a refrigerator. I wouldn't. If you did, you'd buy a cheap one dedicated to that, not a $2000 model.

I highly recommend Calder's "Boat Owner's Mechanical and Electrical Manual", the first few chapters of which cover this whole subject in easy to read detail.

I always thought (rightly or wrongly) that a DC refrigerator has its highest and best use on boats that spend most of their time away from a dock and do not have or can practically use for long periods a gas or diesel generator, and cruise in such a way (ocean crossing for instance) that even running the main engine is to be avoided (sail boats).
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Old 10-28-2015, 06:03 PM   #25
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One thing I might suggest is a fan to pull the heat away from your unit. My old cube was in a closed compartment so I added two fans. One blew at the compressor and the other pulled air out of the compartment.

These were the small computer fans, about 3x3x1" (or maybe 4")

The new unit is at the opposite end of the galley and is positioned by the aft bulkhead. It's got a lot more ventilation (natural) and the area NEVER gets hot. I've got the fans installed and have tested them a few times. The top gets warm now and then I turn on the fans.

It's never hot-hot like the cube. I did upgrade to a Haier 3.1 cubic foot model. That's the smallest unit with a separate freezer door.

Suggestion for whatever unit you do: Buy a weather station (Ambient would be the brand I'd recommend -- about $30 on Amazon) ... get one with an outdoor sensor and put that inside your refrigerator. Now you know at a glance how cool your unit is.

Easy and inexpensive -- my two favorite things.

Good luck.

And yes I opted for AC power with solar and batteries. An Engel would be lovely however I could have bought 4 solar panels for the price of an Engel... When my $120 (on sale from $150) unit bites the dust I'll give it a swimming lesson and get another. The totally inadequate cube was $70 in 2008 and I gave it away -- working. It spent at least three of those years running on a cheap inverter while at anchor.

Just in case you wondered. I'd use what you have until it croaks, AFTER adding some ventilation to the cabinet. If yours is in the galley just to the right of the steps up into the salon, you could poke a hole in the engine room and install a blower to pull air out of the reefer cabinet. That's what I'd do.

Good luck Kurt.

P.S. - The "swimming lesson" was me being facetious
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Old 10-28-2015, 08:15 PM   #26
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So many good replies I'd spend hours replying to each. Here's the short reply:

I've already got a 2000-watt (6000-watt peak) pure sine wave inverter charger, so no extra expense there.

In my experience with units I've owned, if they're AC/DC combinations they're actually DC compressors with an AC transformer to convert AC to DC. I haven't really liked those units and converted the 34-quart AC/DC model on my cat to all DC. If I'm plugged in I'm charging the batteries anyway and if the compressor kicks on when I'm charging via generator there's no "hit" to the AC generator.

Janice, I keep a remote thermostat in my top-load refrigerator on my cat. It is easy, cheap insurance (for the freezer I keep some ice on top - if the ice is melted into a block, power was lost and the food must go!). I'm going to give the 110v refrigerator a try at first. I'll have the woodwork in the galley made to specs that will fit a 12v model just in case, but this is worth trying. I'll have around 600ah in the battery bank, 400-watts of solar, a wind generator and 4.4kw of diesel generator. We'll figure it out during a shake-down cruise.

Note: I forgot to get the model number of the 110v Frigidaire unit I've been talking about that's on the boat, but I seriously doubt it defrosts itself. But if it does I may really reconsider as that is going to use some juice!
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Old 10-28-2015, 08:26 PM   #27
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Update: I comparing the height specifications of the two models that Frigidaire make in this range, it is this one and it is frost-free. I'm going to have to put that into consideration. A nice feature, but likely a power-hog. I'm also trying to figure out where to install/store the 34-quart portable Waeko-Dometic 12v freezer I have on my cat.

Frigidaire 4.5 Cu. Ft. Compact Refrigerator Silver Mist-FFPS4533QM
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Old 10-28-2015, 08:45 PM   #28
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Greetings,
Mr. m. We bought our 110V refrigerator from Home Depot. They have a unit similar to your listed Frigidaire for $229. Not frost free and with what seems a better warranty... Vissani 4.3 cu. ft. Mini Refrigerator in Stainless Look-HVDR430SE - The Home Depot
Just a thought...
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Old 10-29-2015, 06:07 AM   #29
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A couple of years ago we replaced a wornout Norcold with a Summit FF 874 SS 8.1 cuft refrigerator freezer, 115 acv, 370 KWh/year, run amps 1.2, start amps 4.0. I thought a 900 watt inverter would run the unit but it doesn't, is there any way to calculate the size inverter I should use assuming that the 900 watt inverter can't start the unit because it was in a auto defrost mode ? Do I need a pure sine wave inverter ?
Sadly Summit discontinued this unit, it has proved to be quiet, and efficient and we love the convienience of the frost free feature.
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Old 10-30-2015, 12:10 PM   #30
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As a comparison, a super-efficient LG or Samsung digital inverter fridge of 16cf uses about .85 kwhr per day or 320 kwhr per year. A Sunfrost will use about 260 kwhr per year. Admittedly, that's a nice difference.

Difference in cost…. $450 for the household versus $3500 for the Sunfrost.

That extra three grand buys a lot of solar panels, AGMs, inverters, cables, breaker panels, etc. Logically there is no way the Sunfrost can compete when it comes to long term dependability either. So for my money I'd go 110/220v versus 12v.
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Old 10-30-2015, 05:31 PM   #31
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It is really hard to justify the cost of a 12v system when you can fill the need really easily with a household model. If your boat is not going to use 120v routinely then it become easier to swallow the cost. If you plan on leaving the boat at anchor with no one on boards for few days 12v becomes a better option.
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Old 10-30-2015, 10:04 PM   #32
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Mako makes a good point (CaltTexFla made a similar point). My wife and I are still working at this point so money is available to do what needs to be done. But the ROI of an expensive 12v system doesn't seem to be all that great. I've also not personally had great results with Danfoss compressors.
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Old 10-31-2015, 02:27 AM   #33
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If you plan on leaving the boat at anchor with no one on boards for few days 12v becomes a better option.
Since the linear inverter motors do not have start-up power draw, even a 500 watt inverter will run a 15 cf unit. So a modest solar panel should run it while away from the boat.
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Old 10-31-2015, 06:01 AM   #34
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I was thinking going straight 12v is simpler and less can go wrong if no one is on board.
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Old 10-31-2015, 07:50 AM   #35
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"I always thought (rightly or wrongly) that a DC refrigerator has its highest and best use on boats that spend most of their time away from a dock and do not have or can practically use for long periods a gas or diesel generator, and cruise in such a way (ocean crossing for instance) that even running the main engine is to be avoided (sail boats)."

Correct.

For the cruiser that prefers the hook, and quiet , DC is the better choice.

For the gen set daily folks a SOC meter and an alt on the end of the noisemaker will do fine.

All is compromise , use your Cruising Lifestyle , to decide what works for you.

We chose propane , as when cruising we prefer the hook to a marina .

$1000 for the fridge and a bottle of propane a month does it , no noise and hard ice cream!
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Old 10-31-2015, 08:15 AM   #36
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As a comparison, a super-efficient LG or Samsung digital inverter fridge of 16cf uses about .85 kwhr per day or 320 kwhr per year. A Sunfrost will use about 260 kwhr per year. Admittedly, that's a nice difference.

Another similar data point: we've been looking at a 3-door LG for home, 23.7 cu ft, sticker says 683 kWhr/year, $82/year.

$82/year isn't much.

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Old 10-31-2015, 10:19 AM   #37
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I was thinking going straight 12v is simpler and less can go wrong if no one is on board.
The main thing that can go wrong is the same in both set-ups: the batteries go dead. Modern inverters are very reliable. A factor in all this is the weather. If in the 70's or below, the fridge will run infrequently when no one is on board to open it.

When I bought my boat, it did not have an inverter, you had to run the genset for AC when away from the dock. When we brought it down to New Bern from Baltimore, we anchored out or stayed on a free, unserviced public dock. I shut the genset off early at night once everyone stopped using the fridge; in the mornings everything was still cold or frozen in the big Sub Zero (and the water in the water heater was still hot too.)
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Old 10-31-2015, 11:29 AM   #38
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Modern inverters are very reliable.
Most suppliers claim a bathtub curve with a short period of infant mortality followed by 300 years MTBF.
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Old 10-31-2015, 02:21 PM   #39
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Most suppliers claim a bathtub curve with a short period of infant mortality followed by 300 years MTBF.
Sounds about right, for power handling, non-moving parts electronics these days, ventilation and clean tight connections having important roles.

I'm curious where you got the statistic.
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Old 10-31-2015, 02:56 PM   #40
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What type of refrigeration to have joins the best anchor and single vs twin engines debates because there is no single correct answer. It depends on the use to which the refrigeration will be put.
Many residential units are inexpensive, operate on 110/220v and work fine off an inverter or shore power. The inexpensive residential units are built with a price point in mind and for a residential market with unlimited inexpensive electricity. For this reason the manufacturers do not equip these units with expensive but efficient compressors and do not reduce the storage space by adding inches of insulation. This may be changing but when we talk about 110 v residential units we are generally thinking of the $150 or so Home Depot / Sears units which do not have the super efficient compressors.
The expensive end of the marine/rv market has refrigeration units which work off of 12v or 12v/110v(220v in Europe Australia). It is not just the voltage which is different, it is the compressor efficiency and the insulation. My experience and observations are that these units use less than half the electricity of the inexpensive 110v units (although in my case I canot say the Subzero units were inexpensive). I understand that there are 110v units with efficient compressors and greater insulation but I am not aware of their price point.
As I cited earlier in my shift from two Subzero units to two Isotherm units I dropped from over 400 amp hours per day for refrigeration to under 200 amp hours. This was for basically the same size units.
Based on these differences a person who anchors out all the time may want the more efficient units, running the generator to recharge the batteries twice a day is not fun.
A boater who keeps the boat in a marina and anchors occasionally may save a few thousand US dollars by going with the inexpensive 110v residential units and just run the generator when at anchor.
An additional warning, outside of the United States and Canada electricity can be much more expensive. At marinas in Grenada, St. Lucia and Martinique the price of electricity can exceed $1.10 (US) per kilowatt. This is eleven times what I pay for my residential rate in the United States. Refrigeration then becomes expensive.
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