Refrigeration: 110v (inverter) or 12v?

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.

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.

funangler said:

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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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.

I was thinking going straight 12v is simpler and less can go wrong if no one is on board.

"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!

makobuilders said:

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.

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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.

-Chris

funangler said:

I was thinking going straight 12v is simpler and less can go wrong if no one is on board.

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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.)

caltexflanc said:

Modern inverters are very reliable.

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Most suppliers claim a bathtub curve with a short period of infant mortality followed by 300 years MTBF.

Cottontop said:

Most suppliers claim a bathtub curve with a short period of infant mortality followed by 300 years MTBF.

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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.

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.

HiDHo said:

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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Hate to hear that- I installed one a couple of years back- it's been a great unit.


1983 Present 42 Sundeck
Twin Lehman 135's

HiDHo said:

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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Get a plug in Killawatt meter to see what the unit draws. The one thing you won't see is the peak load, since that happens at startup for a second or so. You should size the inverter greater than the fridge requires, and build in some surge or short term peak loading on it for the startup current required to start the compressor.

All motors need a lot more power to start up than they need to run so if you're running motor loads on an inverter, add an extra bit for startup current surge requirements.

Some inverters are better at starting fridges than others. I tried an older 1kW unit and it would not start my bar fridge. Went and bought another new 1kW unit and it works fine.

omc said:

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.

Regards,

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Hey OMC. What fridge make/model do you have that fits the grand banks cupboard?