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Old 29-10-2014, 06:38   #106
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Re: Can a Household Refrigerator Work on a Sailboat ?

With a lot of solar you can have your cake and eat it too.
Here is a Hitachi 14 cu. Ft Refrigerator/ Freezer w/ice
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Old 29-10-2014, 07:00   #107
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Re: Can a Household Refrigerator Work on a Sailboat ?

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A home fridge would be very easy to determine it's energy consumption. Measure the current draw and stick an hour meter on it, I doubt they are variable speed compressors are they?
...
That's what I've done. Ashore I have one building which is on grid with a household AC driven fridge and one which is off grid with DC driven fridge so I can compare. Both about the same CF and the energy use difference is dramatic. But, the AC driven fridge is just a generic cheap fridge. Its my understanding that the new ones are much more efficient.

I have a friend with an off grid house who has installed one of the newer more efficient AC fridges. A Samsung IIRC. He is pleased with it, but I've not tested it with a meter yet. Particularly here in Central America I've discovered the manufactures specs are not accurate. I suspect some just copy an official looking label from another similar device.

For off grid use at home would be nice to find a household unit which is efficient. But on my boat I don't really have a space which would accommodate a standard size/shape fridge. Be a good thing for all when they catch up though and drive prices down.
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Old 29-10-2014, 07:12   #108
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Re: Can a Household Refrigerator Work on a Sailboat ?

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There are two things that you need to be concerned with with any fridge AC or DC. That is operating amp draw and cycle time. While my little dorm fridge,3.5CF, uses 15amps DC (including inverter loss) the hourly load is only 2.5 amps. 24 hour load is less then 55 amps, which the typical 12V system will also use give or take box insulation.

My fridge cycles on for about 2.5 minutes every 14 minutes. A bit more above 95 degrees and less below 60 degrees. The 2.5 minute run time was measured in summer with 90+ degree California delta cabin heat.

A larger fridge actually does not use that many more amps then a small dorm fridge. Though excessive door opening will greatly effect run times as will auto defrost which probably should be disabled for boat life, unless at dock.

The thing to remember is for a given box size the work/btu heat transfer is the same so the over all load per hour will be similar. The 12V units have a smaller compressor, so run longer. But for a given box size a 12V and a 120V compressor will have very similar hourly loads.
Would be interesting to set two up side by side and compare in the same enviroment.

15A DC is certainly manageble, but the 4.7 CF Danfoss BD-35 driven fridge on my boat in the Tropics draws less than 1/3 of that with a similar duty cycle once chilled. Of course the initial cost was many times that of the little dorm fridge.
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Old 29-10-2014, 08:56   #109
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Re: Can a Household Refrigerator Work on a Sailboat ?

I think really it boils down to two things
1. Watts are Watts, doesn't matter if it comes from 12VAC or 12VDC, if the compressor efficiency is similar, then energy consumption will be. I doubt there is much efficiency difference in compressors, but do not know that. However there are conversion losses if you storing 12VDC, but using 120VAC.

2. insulation and type of opening, a well insulated, top opening box will absorb less heat and therefore require less heat to be removed than a box with a front opening and less insulation.

I bet the real answer is, are home refrigerators as well insulated as boat specific fridges? And I bet the answer is, it depends as I bet boat fridges insulation quality is all over the place, some very well insulated, some almost not at all.
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Old 29-10-2014, 10:01   #110
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Re: Can a Household Refrigerator Work on a Sailboat ?

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Originally Posted by sailorchic34 View Post
There are two things that you need to be concerned with with any fridge AC or DC. That is operating amp draw and cycle time. While my little dorm fridge,3.5CF, uses 15amps DC (including inverter loss) the hourly load is only 2.5 amps. 24 hour load is less then 55 amps, which the typical 12V system will also use give or take box insulation.

My fridge cycles on for about 2.5 minutes every 14 minutes. A bit more above 95 degrees and less below 60 degrees. The 2.5 minute run time was measured in summer with 90+ degree California delta cabin heat.

A larger fridge actually does not use that many more amps then a small dorm fridge. Though excessive door opening will greatly effect run times as will auto defrost which probably should be disabled for boat life, unless at dock.

The thing to remember is for a given box size the work/btu heat transfer is the same so the over all load per hour will be similar. The 12V units have a smaller compressor, so run longer. But for a given box size a 12V and a 120V compressor will have very similar hourly loads.
SC has been saying this for a few years now, but the "you have to have a marine fridge" crowd don't seem to want to listen.
Weren't the old Cold Machines 120v compressors with built-into-the-system a dedicated invertor?
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Old 29-10-2014, 10:20   #111
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Re: Can a Household Refrigerator Work on a Sailboat ?

I'm no electrical genius so I just want throw this out here and see what you think.

I was at a big box store where they had dorm fridges. Inside the door is a yellow sticker thats supposed to tell you how many kw it uses per year. A 3.2 cu fridge said 267kw per year. Some quick and dirty math in my head gave me 730 watts per day (270 365) or 60 amps per day (730 12).

My Adler Barbour runs a 3.5cf fridge at about 40+ amps per day, but it is heavily insulated, top loading, and thats just a good estimate made with ten years experience, not an actual measurement.

what do you think?
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Old 29-10-2014, 10:21   #112
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Re: Can a Household Refrigerator Work on a Sailboat ?

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I'm no electrical genius so I just want throw this out here and see what you think.

I was at a big box store where they had dorm fridges. Inside the door is a yellow sticker thats supposed to tell you how many kw it uses per year. A 3.2 cu fridge said 267kw per year. Some quick and dirty math in my head gave me 730 watts per day (270 365) or 60 amps per day (730 12).

what do you think?
Sounds pretty much right on with Sailor Chic's actual experience...
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Old 29-10-2014, 11:30   #113
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Re: Can a Household Refrigerator Work on a Sailboat ?

Would a small chest freezer with one of those gadgets to turn them into kegorator fridges work? Top loading, better insulation, better than a dorm fridge $ for $?

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Old 29-10-2014, 11:31   #114
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Re: Can a Household Refrigerator Work on a Sailboat ?

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Originally Posted by onestepcsy37 View Post
I'm no electrical genius so I just want throw this out here and see what you think.

I was at a big box store where they had dorm fridges. Inside the door is a yellow sticker thats supposed to tell you how many kw it uses per year. A 3.2 cu fridge said 267kw per year. Some quick and dirty math in my head gave me 730 watts per day (270 365) or 60 amps per day (730 12).

My Adler Barbour runs a 3.5cf fridge at about 40+ amps per day, but it is heavily insulated, top loading, and thats just a good estimate made with ten years experience, not an actual measurement.

what do you think?
Throw a few 'hours" in there every now and again and it works.

60 AH is pretty high I think for a built in boat fridge, but hey who knows?

Here Rich claims 24 AH a day for his system and 48 AH for an "evaporator" system, which is a little confusing as they are both vapor cycle aren't they, hence both have evaporators? Either way I understand his point.

CoolBlue Marine Refrigerator System | Cruise RO Water & Power
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Old 29-10-2014, 11:34   #115
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Re: Can a Household Refrigerator Work on a Sailboat ?

Of course you have to have a place to put a home fridge, without a lot of work, most of us don't. I won't consider a home fridge because it would be too much work for me to tear out the ice box etc.
Interesting in theory at least, I can see the potential for significant $savings, plus don't bother with repair, just go to the box store if and when it breaks and get a new, probably more efficient one, that's well, new
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Old 29-10-2014, 13:37   #116
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Re: Can a Household Refrigerator Work on a Sailboat ?

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Be sure to re-orient the compressor if you tip it on it's back
Yes, very important point. Still trying to figure out if the condenser will need to be re-oriented too, can't find any literature on that.

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Old 29-10-2014, 14:07   #117
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Re: Can a Household Refrigerator Work on a Sailboat ?

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...

I was at a big box store where they had dorm fridges. Inside the door is a yellow sticker thats supposed to tell you how many kw it uses per year...
Yeah, beware those little yellow stickers. I've put a meter on a few devices and found the sticker numbers to be rubbish in those cases at least. I suggest you test it before you buy it to confirm.
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Old 29-10-2014, 14:38   #118
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Re: Can a Household Refrigerator Work on a Sailboat ?

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Yes, very important point. Still trying to figure out if the condenser will need to be re-oriented too, can't find any literature on that.

Matt

I don't believe condenser orientation is relevant, someone may correct me on that
as I don't think these little systems separate the oil but circulate it around and I can
see how oil could separate out and sit in the condenser and not circulate, maybe
I don't think that would happen, but it's all I can come up with on condenser orientation
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Old 29-10-2014, 15:05   #119
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Re: Can a Household Refrigerator Work on a Sailboat ?

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Yeah, beware those little yellow stickers. I've put a meter on a few devices and found the sticker numbers to be rubbish in those cases at least. I suggest you test it before you buy it to confirm.
The number is probably some calculated average and not real world experience. Take it with a grain of salt, although as a64pilot says, sailorchic34 reports similar numbers from her 3.2cf dorm fridge.

This should probably be in the "cruising on $500 a month" thread. Few of us can stretch a buck like sailorchic, and this is the route she has taken. Being an electrical engineer makes her opinion a bit more believable.

I paid over $1200 for my adler barbour, although its worked flawlessly for ten years, so no complaints. Sailorchic has maybe $100 in a fridge and $50 in an inverter and will simply replace either when they break. We both have similar battery and solar panel expenses, so no savings there.
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Old 30-10-2014, 06:32   #120
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Re: Can a Household Refrigerator Work on a Sailboat ?

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145W average at 120V is I believe a little more than 12 amps at 12V (still 145 watts of course), or a little more than double the average Danfoss draw I believe. But if you rarely open it, you may get by with just a little more than twice the energy draw of a typical marine unit. I think that is the answer really, if your OK with using twice the energy, a home unit will be fine.
Volts does not matter, watts are watts. Mine is 230V.
My point was the convenience to use, not the efficiency. For efficiency, nothing beats our traditional piano fridge with BD50 compressor. But to find a small thing in it is no easy task. In the home unit you have the place for everything.

I will test it and report real world numbers. And we run low on batteries, we can always turn it off, and use the 12V fridge.
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