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Old 10-24-2015, 11:27 AM   #1
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Refrigeration: 110v (inverter) or 12v?

As my Gulfstar 36 refit project begins I've got some electrical decisions to make. The boat came with a rather nice 110v half-size freezer/refrigerator combination. I'm installing an inverter/charger combo that can more than handle the load (Pure Sine Wave 2000-watt continuous, 6000-watt peak I believe). The house bank isn't finalized yet but I'm most likely going with 400 to 600 amp hours. My current boat (30' power cat) has all 12v refrigeration and we can anchor for days with 235 watts of solar and just a few hours of generator usage. The Gulfstar will have 400 watts of solar plus a wind generator for the islands. With all that said what is your opinion of running 110v refrigeration off an inverter versus replacing it with a 12v system. Friends with experience I speak with give conflicting opinions (imagine that! :-).

Thanks!
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Old 10-24-2015, 11:38 AM   #2
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Quote:
Originally Posted by mixman View Post
As my Gulfstar 36 refit project begins I've got some electrical decisions to make. The boat came with a rather nice 110v half-size freezer/refrigerator combination. I'm installing an inverter/charger combo that can more than handle the load (Pure Sine Wave 2000-watt continuous, 6000-watt peak I believe). The house bank isn't finalized yet but I'm most likely going with 400 to 600 amp hours. My current boat (30' power cat) has all 12v refrigeration and we can anchor for days with 235 watts of solar and just a few hours of generator usage. The Gulfstar will have 400 watts of solar plus a wind generator for the islands. With all that said what is your opinion of running 110v refrigeration off an inverter versus replacing it with a 12v system. Friends with experience I speak with give conflicting opinions (imagine that! :-).

Thanks!
Does the efficiency improve with the 12vdc unit? If not substantially then why waste the money changing it.
They're both drawing power from the same source at the end of the day.
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Old 10-24-2015, 11:44 AM   #3
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I went with a "bar sized" domestic fridge/freezer that runs on AC, easily powered by a 1000w inverter. It only draws about 1.5A AC while running, so under 200w. I went this route as fridge is inexpensive and a standard size. If it poops, I can replace it for under 200 bucks at any big box store.

Measure how many amps your fridge takes to run. Sounds like with your solar, wind and bank size you will be in good shape.

The marine specific DC/AC fridges have caused lots of folks trouble, and are expensive. I wanted to avoid that.
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Old 10-24-2015, 11:48 AM   #4
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I think 12v units are more efficient (if nothing else, due to the inefficiency of inverters), but I've had my share of problems with 12v units. On my 30' power cat I run one of those $150 portable ice makers off inverter and it draws hardly anything.

You both make good points. Thanks.
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Old 10-24-2015, 12:05 PM   #5
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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.

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Old 10-24-2015, 12:12 PM   #6
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AC or DC

Hi !

My Grand Banks has 2 x 12 v fridges on board. Service battery bank is : 6 X 6 volts AGM batteries, 170 amp each. I can stay easily at the anchor 48 hours long without using my Onan generator, both fridges on, batteries still 45% of charge. I don't have solar or wind generator.

A friend of mine own a Trader 41 + 2 with 1 x 220 volts fridge (same size as 1 of mine), 2 x 12 volts service batteries, 200 amp each. His fridge is connected with a pure sine wave 2000 w inverter.


After 16 hours long at the anchor, his batteries died. So, be aware an inverter needs lot of power (as much as the fridge).

From my opinion only, I am very happy with my 12 volts DC fridge, I would never remplace them for any AC units.

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Old 10-24-2015, 12:22 PM   #7
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It is true the DC units will be more efficient, or should be. He already has a AC unit, so there is a cost issue to consider. Also important to know if there is a gen on board. Nothing wrong with running it evey day or two to top up batts if solar and wind and main engine use can't keep batts up.

Also need to know running amps of fridge. Some older ones are truly power hogs.
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Old 10-24-2015, 12:45 PM   #8
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I have a 12V/110V Norcold fridge/freezer and a 110V apartment size fridge/freezer. The Norcold switches to 110V when shore power or generator are on and runs at 12V the other times. The 110V runs on a small 1000W MSW inverter and is mounted securely on a countertop to ensure adequate air circulation along its heat-dissipating sides, a critical issue for this model.

My total load with LED lights, 2 fridges, various electronics and small chargers, fans and TV/stereo entertainment runs about 150-200AH per day. The greatest loads are in the summer with extra cooling needed for the fridges and fan operation.

If you have the solar and wind power to support the electrical needs of the 110V fridge, I'd go that route. If you find it's not sufficient to support the 110V fridge, you can always change it out later to a 12V model with better efficiency. It would be a simple matter to test this at the slip with shore power disconnected. A Kill-a-Watt meter will help you to quantify the electrical loads on your vessel.

Mixman, drop me a PM sometime. I've been thinking about Billy and was wondering how he's doing. Are you still in touch?
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Old 10-24-2015, 01:50 PM   #9
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I think 12v units are more efficient (if nothing else, due to the inefficiency of inverters), but I've had my share of problems with 12v units. On my 30' power cat I run one of those $150 portable ice makers off inverter and it draws hardly anything.
Conversion of energy requires energy which is lost as heat generated. That's the reason why your inverter has a fan, since during the power conversion, you lose some of the power you are converting in the form of heat. Plus some loss in the boost circuitry. If you had a bank of 10 batteries running into an inverter, your loss would be minimal, since all it would be doing is taking DC and forming the sine wave AC on the output.

It is always better to use power in the form it is currently in, especially DC.
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Old 10-24-2015, 04:44 PM   #10
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Another viewpoint, it is not so much the 110v (220v) vs 12 volt, or the inverter inefficiency which makes a difference. What can make a difference is both the condenser and the insulation. Many/most 110v domestic units use fairly inefficient condensers and have little insulation. These are designed for the home market where electricity is plentiful and cheap and the condenser is a great place to reduce the price point of the unit. The same is true of the insulation.

A high end 12v marine unit has the very efficient Danfoss compressor, many accepting both 12 volt and 110v. The insulation is usually better. Some of the 12 volt units even have separate doors covering each shelf of the freezer.

When I switched from SubZero 110v units to Isotherm 110v/12v units my electricity usage was more than cut in half.
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Old 10-24-2015, 05:51 PM   #11
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Good view

Quote:
Originally Posted by Bay Pelican View Post
Another viewpoint, it is not so much the 110v (220v) vs 12 volt, or the inverter inefficiency which makes a difference. What can make a difference is both the condenser and the insulation. Many/most 110v domestic units use fairly inefficient condensers and have little insulation. These are designed for the home market where electricity is plentiful and cheap and the condenser is a great place to reduce the price point of the unit. The same is true of the insulation.

A high end 12v marine unit has the very efficient Danfoss compressor, many accepting both 12 volt and 110v. The insulation is usually better. Some of the 12 volt units even have separate doors covering each shelf of the freezer.

When I switched from SubZero 110v units to Isotherm 110v/12v units my electricity usage was more than cut in half.
That's very true.
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Old 10-24-2015, 09:42 PM   #12
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If you had a bank of 10 batteries running into an inverter, your loss would be minimal, since all it would be doing is taking DC and forming the sine wave AC on the output.

Everyone I ask for one of these "boxes" says no-can-do, no-such-thing'
I've already got the battery bank.

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Old 10-24-2015, 10:26 PM   #13
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Thanks everyone. Many good points to consider. I do have a 4.4kw genset on the Gulfstar. There is no "box" to convert to DC refrigeration so that would have to be a custom project . My power cat has a box that I've put 3 different 12v systems in and out of over the years, so I'm quite familiar with Danfoss compressors and I always carry manifolds and R134a to keep them charged correctly (I've had to learn how to do that stuff the hard way).

Al, PM sent.
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Old 10-25-2015, 08:31 AM   #14
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Quote:
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When I switched from SubZero 110v units to Isotherm 110v/12v units my electricity usage was more than cut in half.
Same experience here. I had an apartment-size home fridge the PO had installed. I replaced it with the same marine version that originally came with the boat (even the screw holes lined up.) I found it used a lot less electricity. I went from being able to go less than 12 hours on my house bank (before hitting 50%) to at least 24 hours.

Some might say it wasn't worth it. It cost a lot more than an apartment fridge. I still run the genset once or twice a day if I'm at anchor or on a mooring, so I technically didn't need the extra efficiency.

On the plus side: It looks great. When I want to, I can skip running the genset. If the genset fails, I'll be OK for much longer; just motoring a few hours will recharge everything. If I install solar I might never need the genset at all. Less stress worrying about where my next hundred Amp-Hours are coming from is a good thing.

Overall, I'm glad I went this route.
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Old 10-25-2015, 08:35 AM   #15
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The boat came with a rather nice 110v half-size freezer/refrigerator combination. I'm installing an inverter/charger combo that can more than handle the load (Pure Sine Wave 2000-watt continuous, 6000-watt peak I believe).

For a new install, I'd prefer the 12V/120V (DC/AC) versions like we have now (happen to be NovaKool).

In your case, sounds like you can do nothing (about the "rather nice" existing fridge) until it craps out.

I wonder if the frost-free feature in household AC fridges might account for some of their extra energy consumption. Wouldn't mind having that, too...

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Old 10-25-2015, 08:48 AM   #16
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Some of the math here is off a bit, using watts. Compare the kw/hr ratings of like sized and featured fridge freezer combos, and it comes very close 12v vs 110. Then compare price. It will take a long time to make up the total cost of ownership difference.
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Old 10-25-2015, 08:59 AM   #17
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Hi George!

This is interesting:

Norcold AC / DC Series - Model No. DE0061
Current Draw:
5.4 Amp @ 12 Volt DC
2.2 Amp @ 24 Volt DC
0.9 Amp @ 120 Volt AC
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Old 10-28-2015, 07:43 AM   #18
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"Does the efficiency improve with the 12vdc unit? "

Depends on the smarts of the DC unit.

A modern style like a Danfoss will run slower and use far less energy as the computer works out the load.

Also many will run full speed to a lower temp while it senses the engine is operating.

Higher voltage gives more (tho less efficient) cooling , drops back to most efficient when simply battery powered.

Beware of the amp ratings on house units as they do not include the heating elements required to defrost thin insulation .

Sunfrost is great , but does not fit too many boats.

  1. Energy Efficient Refrigerators - SunFrost.com

    www.sunfrost.com/all_efficient_refrigerator_models.htmlCached

    Sun Frost refrigerators and freezers are so outstandingly energy-efficient, powering a home with solar power or other low output energy sources ...



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Old 10-28-2015, 09:35 AM   #19
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I voted for the cheap 110v unit and an inverter. It's been working for over 15 years and I'm not afraid if I have to replace it. It would be smaller, better and cheaper.

But that goes pretty much for the whole boat.
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Old 10-28-2015, 11:11 AM   #20
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Quote:
Originally Posted by mixman View Post
Hi George!

This is interesting:

Norcold AC / DC Series - Model No. DE0061
Current Draw:
5.4 Amp @ 12 Volt DC
2.2 Amp @ 24 Volt DC
0.9 Amp @ 120 Volt AC
I could be wrong, but it looks from the manual that it is DC "native" and that it converts AC to DC, which would make AC less efficient. Looking at the price for that unit, vs what a straight 120 volt reefer of the same size costs, it would take a long time for that to pay back.
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