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Old 11-07-2020, 12:25   #1
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Looking to covert to 12v refridgeration

I am looking to change our refrigeration from 120vac to 12vdc. We are adding an arch, solar and two more batteries to increase our capacity.
The refrigeration will be done at the same time.
We currently have a water cooled system with a 120vac compressor and holding plate.
We will be mostly in tropical regions.
If you were doing it from scratch, which direction would you go?
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Old 11-07-2020, 14:27   #2
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Re: Looking to covert to 12v refridgeration

A 47 foot boat generally has one large or two boxes totaling 10 cubic feet or larger and this is the main reason AC electrical refrigeration was used. You may find supporting energy for 12 volt refrigeration a problem unless you still plan to run a generator to charge batteries.
The first thing to do is to determine if you can support the daily 12 volt power requirement amps or watts of 12 volt refrigeration. Normally small 12 volt systems are 20% to 50 more efficient than the 110 volt units but plan for only the 20% energy improvement for a large box.

Determine amp-hours or watt hours required to operate present unit for a day recording ambient temperature day of your test. Now reduce test figure by 20% then adjust amperage or watts of energy required for tropical weather 89 degrees F cruising and increase 4 amp-hrs per degree differential. Example if test was done at an ambient temperature 64 degrees then at 89 degrees F twice as much energy will be required.
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Old 11-07-2020, 14:34   #3
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Re: Looking to covert to 12v refridgeration

Buy a power meter that plugs into a wall outlet and plug your fridge in the meter. Record power usage over a couple of days as you note also the ambient temperature. This will give you a base from which to extrapolate and make calculations for your plans.
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Old 11-07-2020, 14:49   #4
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Re: Looking to covert to 12v refridgeration

This is a NZ company but these products are available world wide.

https://www.fridgetech.co.nz/collect...kitsets?page=1

You can find a unit to suit your needs at a price that is not cheap but market related and if chosen correctly, will perform within the range of your 12v electrical system.

I have two of these, one for the refrigerator and one for the freezer. Together they draw about 10.5A when they’re both running, account for about 125Ah a day in warm weather which my solar array puts back in a couple of sunny hours.

No possible way a mains unit could beat these little fellows, at least not in my experience.
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Old 12-07-2020, 07:56   #5
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Re: Looking to covert to 12v refridgeration

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Originally Posted by sailormed View Post
Buy a power meter that plugs into a wall outlet and plug your fridge in the meter. Record power usage over a couple of days as you note also the ambient temperature. This will give you a base from which to extrapolate and make calculations for your plans.
Thanks all for the information.
The only issue I have in measuring the current system is the current setup.uses a cold plate. Most refrigeration people suggest going to a conventional evaporator.
Would this be an apples to oranges comparison?
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Old 12-07-2020, 08:27   #6
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Re: Looking to covert to 12v refridgeration

You also have the option of getting an all in one portable fridge/freezer.

We bought an ARB Fridge and it is awesome. You can use the old fridge space as a dedicated freezer. That is our plan. Eventually.
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Old 12-07-2020, 09:05   #7
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Re: Looking to covert to 12v refridgeration

I am in the process of rebuilding a fridge myself. My current 12V system has bit the dust. I have a completely separate fridge and freezer with holdover plates. My fridge was water cooled and I am keeping that system. I am also reusing the holdover plates. I have a friend who is in that business and he is building me a new system. I have purchased 2 compressors, one for the fridge and one for the freezer, they have different cooling capacities, both 1/5 hp. Each will have it's own thermostat, expansion valve, sight glass, pressure gauge and cooling coils. It will all fit onto the same shelf as my old compressor because the old one was huge. The compressors all come wired for AC so each needs an inverter to work off DC. I opted for separate inverters because there is no reason to have an inverter on when the compressor is not on. Also, if I should ever have an issue with one, I have a back up.


We calculate the system to require about 25 amps with both compressors running full out. It should cool things down quickly, so the compressors should run only a couple hours every 24 hours once fridge is to temp. So, at 50 to 75 Amps per day you are more efficient than most evaporator type fridges.


I have 400 watts of solar panels and a windgen and 400 Amps of Lithium batts. I figure I can run the system easily anywhere.
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Old 12-07-2020, 09:25   #8
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Re: Looking to covert to 12v refridgeration

Quote:
Originally Posted by lifeofreilly57 View Post
Thanks all for the information.
The only issue I have in measuring the current system is the current setup.uses a cold plate. Most refrigeration people suggest going to a conventional evaporator.
Would this be an apples to oranges comparison?
Richard Collman and Ozepete battled on the subject of cold plates V evaporator plates in a thread a couple of years ago. Since they are both pretty expert the thread contains a lot of good information on the subject.

Ozepete's company manufactures boat refrigeration systems and ran side by side tests on both systems. In addition to the economic consequences of not so violently cycling batteries by exploiting the high electrical power availability during the daylight hours the power savings achieved by the use of cold plates reducing compressor cycling was substantial.

If you already have the cold plates installed it would appear imprudent to convert back to a less efficient system.
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Old 12-07-2020, 10:14   #9
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Re: Looking to covert to 12v refridgeration

I went through this last year for the same reason and had a post asking people out cruising now in the tropics what their experience was. Would the thin plate evaporation system work?

OzPete apparently has been banned from CF. Too bad. Richard Kollman knows his stuff too.

I worked with both of them at great length. I really liked Oz Pete's system. Very slick. In the end I opted to go with 2 separate Nova Kool systems. About the same as OzPete's system which is a single system with spillover. I liked the simplicity of the thin plate. I like that I have 2 separate systems that can be either fridge or freezer. If one stops... no big deal. Frustrating but not a big deal.

I had tried the all in one drop in box and hated it. Ended up with what I have now. I also took the opportunity to replace all the 25 year old foam with all new stuff and way thicker. 6" on the bottom, 5" on the sides, 4" on the top. This is the biggest bang for your buck you can do. My top opening lids are hinged and lock down on the other side against the seal.
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Old 12-07-2020, 10:18   #10
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Re: Looking to covert to 12v refridgeration

Quote:
Originally Posted by lifeofreilly57 View Post
Thanks all for the information.
The only issue I have in measuring the current system is the current setup.uses a cold plate. Most refrigeration people suggest going to a conventional evaporator.
Would this be an apples to oranges comparison?
The answer to standard thin evaporators versus thick evaporator plates is where the energy comes from, is there a surplus of energy produced by refrigeration compressor. Both use the same amount of compressor energy and produce the same amount of heat energy removed from refrigerated box. Large refrigerant compressors produce surplus energy that can be stored in eutectic substance plate where small compressors systems do not benefit from. For boats with alternative energy from wind, solar, and small generators and small 12 volt refrigeration units do perform well in the right heat loaded size boxes.

Eutectic plates are the solution for a single temperature cold beer box but they do not have the utility of separate temperature areas that the many shapes and sizes of a standard type evaporator provide.
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Old 12-07-2020, 13:10   #11
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Re: Looking to covert to 12v refridgeration

We are revamping a 25 year old Seafrost system, 3 holding plates with dual coils driven by an engine drive compressor and shore assist 120 volt that has given great service.
We have removed the 120 volt compressor and are replacing it with two 12volt units. One 12 volt compressor will service the two freezer plates and one compressor will service the refer plate.
The reason for the change is to be able to anchor long term without runing the engine. Expect that our 550 watts of solar can handle the load. Anytime the engine is on the engine drive compressor will give 10 to 20 hours of holdover and provides redundancy.
That said taking out the 40 year old insulation and replacing it with R 40 all around has probably been the most important change
Tom
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Old 12-07-2020, 14:41   #12
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Re: Looking to covert to 12v refridgeration

Don't mean to high jack this thread, but i do not know how to ask a question on this forum !, i need to ask Richard a number of question's, please help. Thanks, Doug.
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Old 12-07-2020, 15:07   #13
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Re: Looking to covert to 12v refridgeration

There is a ton of competent, professional information on this forum, especially from Richard Kollman but also OzPete and others. This is really a case of using search and you will find all of the answers you need, and then some. Not that you shouldn't ask questions; just get up to speed with some of the existing threads first. Also read through Kollman's web site.

An important point which usually gets mentioned is to first evaluate the current boxes for efficiency: most production built-in fridges are poorly insulated, and in that case the most efficient compressor in the world won't get the electrical consumption down. With the evaporator plates and plumbing out it is the best time to upgrade the insulation. There are improved alternatives for insulating these days, and they are discussed at length in other threads: search is your friend.

Personally I have been very happy with a 12VDC system that uses a keel cooler in the refrigerant flow for condensing. I have had seawater-cooled systems before and would recommend avoiding them like the plague. But I am just one cruiser; read what the pros have to say.

Greg
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Old 12-07-2020, 15:11   #14
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Re: Looking to covert to 12v refridgeration

Quote:
Originally Posted by lifeofreilly57 View Post
I am looking to change our refrigeration from 120vac to 12vdc. We are adding an arch, solar and two more batteries to increase our capacity.
The refrigeration will be done at the same time.
We currently have a water cooled system with a 120vac compressor and holding plate.
We will be mostly in tropical regions.
If you were doing it from scratch, which direction would you go?
I think I would seriously consider a small inverter just to power the refrigerator first.
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Old 12-07-2020, 15:48   #15
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Re: Looking to covert to 12v refridgeration

Quote:
Originally Posted by tml View Post
We are revamping a 25 year old Seafrost system, 3 holding plates with dual coils driven by an engine drive compressor and shore assist 120 volt that has given great service.
We have removed the 120 volt compressor and are replacing it with two 12volt units. One 12 volt compressor will service the two freezer plates and one compressor will service the refer plate.
The reason for the change is to be able to anchor long term without runing the engine. Expect that our 550 watts of solar can handle the load. Anytime the engine is on the engine drive compressor will give 10 to 20 hours of holdover and provides redundancy.
That said taking out the 40 year old insulation and replacing it with R 40 all around has probably been the most important change
Tom
I hope you are using large enough replacement compressors because the old Seafrost plate evaporator tubing is generally oversize lowering necessary oil return velocity to compressor. Check with Cleave at Seafrost before making a mistake. The new compressor's return tubing size is what determines tubing diameter size coil is to be used in any evaporator. Tubing slightly larger is sometimes OK but twice the size can and did cause failures in three boats.
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