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  Topic Review (Newest First)
04-08-2005 05:21 AM

Steve, the key to using the existing 110 volt system holding plate coil for a small 12 volt system will again be the tubing size inside the plate and not the compressor tubing size.
If the plate tubing is too large a separate evaporator will be required.
Alternative energy from wind or sun is a good idea for boats with Swing or Danfoss compressor refrigeration. My rule is, fifty watts of power per cubic foot of box, per day when sizing solar panels.
04-05-2005 07:34 AM


Thanks for your informative reply. Your information is straight forward and directly answers many of the questions I have. I sure appreciate it.

I haven''t been able to see your slide show (software issue on my end). I''ll be happy to move this discussion over to your forum, but thought it appropriate to respond here first.

I can add a little more light on my situation. My "shore-power" system is a 1984, off-the-self, air cooled condensing unit (model 2314 sticks in my mind). It uses 1/8" copper flare fittings and pumped R-12. Both it and the engine unit were "dead" when I got the boat. I reinstalled the engine unit (sanden 505) and charged both systems. The engine side has been great. The electric unit has always needed help. With the lack of consumer available R-12, I opted to use aftermarket Enviro-Safe product with good success. The last charge had a dye-charge in it, so I''ll go and start looking for leaks on the electric side.

So, from your last post, I take it that I can in fact remove the electric unit and install a danforth type 12 volt condensing unit, assuming everything else is good. That would be excellent, as I have had great luck with the hold-over plate set up and I don''t mind charging when the engine is running. When cruising, I run the engine enough to handle the bulk of work, but would like to avoid running the engine at anchor just to cool the box. At 30-50 (or even 80) amps a day, with my solar panels and soon to be added wind generator, I should be able to go two or three days w/o out running the engine. That is my real goal here. Off the inverter, my electric unit draws 100a/hour.

See you on your web site.

04-04-2005 02:26 PM

Steve, Fleming refrigeration systems are excellent systems. The addition of a 110 volt dual system was sometimes called a shore power system, unless the boat was equipped with a generator.

As to finding the leak in the 110 volt side I would insert fluorescent dye in with a refrigerant charge, then immediately remove the water hoses from the condenser and replace them with balloons to see if the leak is in the seawater condenser. After the condenser checks out reconnect hoses and run the system as much as you can to allow the dye to find the leak. Any small black light will make the leak visible if it is external. Leaks inside holding plates will cause severe distortion of a holding plate. Severe distortion means the plate will look like a football, I am assuming the plate’s fill plug is still in place and tight.

Now to answer your questions:
To use another system connected to the holding plates it must match the capacity of the existing system. The key to your question will be the size of the tubing inside the plate. If the plate tubing is ½ inch OD a large 12 volt replacement is required. Plate tubing of ¼ to 5/16 OD would allow a 12 volt Danfoss compressor like an Adler Barbour to be connected to a plate. On a boat with a standard DC power system there is a good chance with a large 12 volt system the engine must be run to support the large systems.

I don’t know the size of your box or boxes, but if you have watched my slide show or read my 12 volt book you will be able to evaluate what compressor has the capacity to support the refrigerator. Your friends Norcold unit has either one or two Swing compressors in it, Swing compressor and others pictured in slide show.

Yes, there are ways to add a small 12 volt unit to the existing box without disturbing the holding plate systems. If you will send box sizes and plate sizes and locations I will give you some recommendations. It is best to e mail or use my refrigeration forum.

From the author of four books on boat refrigeration
04-03-2005 02:18 PM

That is why I asked about the Waeco unit in my eariler post.

I currently have an old dual circuit Fleming Marine unit with twin hold over plates. One circuit is for the engine driven/water cooled unit (which is awsome), and the other is for a 110v AC, air-cooled condensing unit, which has been ok until we began cruising. It draws too much power for running with out shore power - something like 100amps off of my inverter. Plus, it cools much slower than the engine driven unit. Both, however can freeze my box, to the point where I have partitioned off one plate for use as a freezer. It can actually freeze meats in the FL Keys, as well as freeze my beer.

However, the 110v condensing unit has developed a a bad leak and no longer holds and adaquate charge. The engine unit is good, but I don''t like running the engine just to cool the box.

I have a friend with the same boat (Westsail 32) and box (9 cu. ft) who has had great luck with a norcold conversion unit. I don''t know which condenser unit it uses, but it only draws 4 amps and is self tending. He is very happy with it.

Point of all this is that it makes sense to me to convert over to a newer unit that draws less power and is more self tending than what I have. The water cooled Danfoss unit seems to make sense in my situation.


Could I adapt at newer 12 volt unit to replace the old 110 volt electric unit and keep my hold over plates intact? Assuming, of course, the leak is not inside the plates.

04-02-2005 07:35 PM

Richard, I''ve done the best job I can in the time I''ve had - we''re readying the boat to leave London on the next tide - to explain to this thread''s readers what I''ve experienced. I''ll leave it to you to offer up the seminar; my contributions are based on what I''ve seen and experienced myself.

One general observation: When you say "Jack, it is unusual to find anyone who has lived aboard with a water cooled Danfoss BD condensing unit that likes it." you are telling me that you have not been out among cruising boats in the field to the extent you may think you have. In the last 5 years, thru-out the Caribbean, the U.S. east coast, and now all of N Europe, my observation would be exactly the opposite of this. I don''t think we''ve - yet - met a single user of a Danfoss watercooled unit that a) was experiencing what they thought was poor performance, or b) had problems with their units. And this includes a testy engineer in Trinidad who did all kinds of tests with various units and cooling methods before ending up switching over to a water-cooled, Danfoss-based system. I''m sure there are some disappointed customers out there...there always are. But they must be quite small in number.

Cheers to everyone...

04-01-2005 07:45 AM

Jack, it is unusual to find anyone who has lived aboard with a water cooled Danfoss BD condensing unit that likes it. You are right there are no simple black and white answers about selection ice box conversion refrigeration units.

The days of selling products on the merits of their actual performance is over the real pioneers in boat refrigeration manufacturing and service are gone and it is now a catalog sales business. I guess I see the darkest side, those boaters that are dissatisfied with the unit or the people they bought it from. I have tried to cover in detail the small 12 volt refrigeration story in my 12/24 Volt Refrigeration Manual, the book also evaluates the manufactures. On the subject of selecting equipment the slide show on my web site is as good of an explanation as you will find on the subject and its free.

European manufacturers of these small 12 volt systems concentrate on the volume sales markets, small boats in non tropical waters. If a box to be converted to refrigeration is over four cubic feet and used in tropical waters Isotherm and WAECO do not have a suitable unit for a true refrigerator conversion. Seawater temperature plays an important role in selecting the type of refrigeration because it effects the boats interior temperature and the refrigerators performance. For more on this see FAQ 33 on my web site.

When a small 12 volt refrigeration unit is selected for a specific boat an application engineer or in most cases the boat owner should review all the available unit specifications. The important items effecting the equipment selection are:

Box Size and Shape
Even with today’s high output alternators and smart voltage regulators there is a limit to how large a box that can be refrigerated with 12 volt power. When the daily total boat 12 volt amp hours exceed 100 its time to consider some type of alternative energy source or another type of refrigeration unless the engine alternator is to be run several hours a day.
The box’s size, amount of insulation and the owners intended use will provide enough information to determine daily required capacity. Manufacturers are not always helpful in providing system capacity information here is what one sales brochure says. ( BD50 compressor will handle a 8.1 cu. ft. box consuming One amp per hour average. In small print; With ambient water temperature of 72 degree F.) Bad info.
There are those that try to convince you that it is possible to use figures from a mechanical engineering book to determine the Btu heat load of a pleasure boat ice box, bad advise these boxes are not walk in coolers.

The shape of a box and lid opening in most cases will determine the type and size of the evaporator. The evaporator should be mounted high in the box. A freezer evaporator should surround the food product as much as possible. A small box or one with a tapered side is difficult to convert to a true refrigerator which means it also has a freezing section.
On the small boxes where the lid is large enough a chamber evaporator (bin) can convert the box into a true refrigerator with a freezing section.

Condensing Unit Location
The air cooled condensing unit must be located in a spot where the air that passes through it is not allowed to pass through it again.
Condensing units that are water cooled do not have a fan to assist in compressor cooling. This means that the only source of compressor cooling is the returning refrigerant that may be insufficient if the compressor is in a confined space.

Required Compressor Capacity
Select a compressor and its most efficient speed that will provide less than a 50% duty cycle.

Required Evaporator Capacity
It there are times when a compressor is to be operated at max capacity the evaporator or holding plate must be sized to except that capacity. Example, a BD50 compressor at 3500 rpm needs a evaporator/holding plate with 500 square inches of surface skin area to be efficient.
A large holding plate may be selected as a means of storing addition energy from alternative power sources.

Gas to Liquid Condenser Capacity
It is the job of the condenser to see that liquid is delivered to the expansion device near the evaporator in the correct pressure range. If the air or water used as a cooling medium across the condenser coil is too cold or too warm, system efficiency is lost. A properly installed Danfoss compressor air cooled system can be left unattended for months this is not possible with a water cooled system.

There is a lot of boat refrigeration information on my web site including a refrieration forum at

03-31-2005 09:29 PM

Richard, just a couple of thoughts to flush out the discussion a bit.

"The water pump systems are generally less efficient in warm water than air cooled and destroy the energy advantage of the of the variable speed compressors."

I''m not sure about the last statement as I have not yet used a variable speed compressor. However, for systems without these compressors, I doubt water cooling is categorically less energy efficient as that would depend on the draw of the water pump vs. the additional cooling value of water over hot tropical air. My experience suggest water cooling is going to be measurably better. I''ve also watched others experiment with water cooling in their boats (we had quite a group doing this down in Trinidad) and they found the same results I did. Insofar as ''reliability'' is concerned, I suspect your view on water cooling being less reliabile is drawn from so many systems using raw (salt) water, which does indeed bring aboard a lot of compromises. In 10 years of water-cooling reefer use, full-time, we''ve never had an issue with the water cooling feature because there really isn''t anything to go wrong unless the pump breaks. (I lied there... We need to clean the screen filter occasionally.)

I completely agree with your two main points stated upfront, and everyone reading this thread would help themselves by pondering them: everyone has their own preferences re: refrigeration (some want a meat locker!) and different boxes (and I would add, boat electrical systems, and lifestyles, and the waters in which the boat is used) can all be better or worse candidates for a given reefer system.

I can''t speak to your comments about Isotherm having no interest in after-sales service, except to note that it''s dealers who must provide service and dealer performance is so varied in quality and availability that probably any general comment is going to miss the mark. You may believe Isotherm is intended more for boats in cooler climates because they are a N European company and have deep market penetration here...but we saw excellent service from our Isotherm unit for 4 years in Florida and 2 in the Caribbean, so I''m not sure what else to expect of a system that our Isotherm system isn''t providing.

Just more food for thought... No simple, black & white answers (or even questions) here!

03-31-2005 04:15 PM

Jack, I know I won’t Change your mind and I am sure you believe what you say but I would like to point out a few things regarding boat ice box conversion units. After building several hundred holding plates and working with at least 1000 boaters I did form some strong opinions about what works and what does not. The degree of refrigeration temperature acceptance varies from one boater to another. If you ask all boaters which refrigeration is best there will be someone who like every system sold.

The facts are that no one ice box conversion system fits all boats or meets all owners needs. Another thing to remember is that the efficiency of all refrigeration systems are not the same. The efficiency of an engine driven or large 12 volt system is rarely of concern because they both depend on the engine running. The concern with these large holding plate systems was how much energy could be transferred to the plates in a short period of tome. When it comes to these new small new variable speed 12 volt Danfoss compressors run time is no longer important. The System Coefficient Of Performance (SCOP) now allows manufacturers to have higher efficiency than was possible with the older compressors. The Isotherm holding plate systems are a good match for small boxes of less than four cubic feet in tropical, they even say this in their installation guide. One key to a holding plate’s performance is the amount of surface area must be able to absorb the heat capacity equal to the compressors output. In my opinion Isotherm no longer has an interest in after market support and their designs are for the cooler climates. If you want to compare the Danfoss compressor systems connected to holding plates I am sure the Technautics Cool Blue would be the most efficient in comparable boxes.

History has proven that pumped water cooling these small compressor systems results in poor system reliability. The water pump systems are generally less efficient in warm water than air cooled and destroy the energy advantage of the of the variable speed compressors.

03-28-2005 06:03 AM

Jim, I only have experience with the alcohol-filled holding plate of our Isotherm system...and it isn''t their large plate, either. So I can''t offer a first-hand comparison with e.g. Technautics plates which, as I understand it, use a glycol solution. Having said that, a friend rebuilt his Westsail icebox (perhaps that will give you a feel for dimensions and shape) with >4" closed cell foam on all sides and then installed a Technautics system. The system worked well but he was consuming 65-70 amp/hrs/day, sometimes more, so this was certainly no silver bullet re: efficiency. I would gauge his dimensions to be 50% larger than our approx. 5 cu ft box (which was the one drawing the 30-35 amp/hrs/day). These measurements were all taken with a Link 2000R (both boats) and in Bahamas/Florida spring/summer weather with water temps around 80F.

Re: what you can expect from a freezer, my impression is that it depends a lot on how clever you are, as well as how big the box and the freezer section, of course. When I installed the Isotherm, I riveted up an aluminum box not quite as deep (top to bottom) as the holding plate, and a bit narrower. I riveted on a bracket which hung over the top of the plate and slipped down its back side. This left the metal freezer box fitting next to (and touching) the plate, so lots of transfer. That''s worked great and no one has bigger/clearer icecubes...but in reality, I now realize I''m not using the coldest part of the box and would, at the least, build the freezer box all the way down the plate to the bottom of the larger box - that''s where the cold air hides!<g>

Our little freezer box has two vertical aluminum ice cube trays and some minor food items in it; it''s capacity is probably 5 or 6 of those ice cube trays. Not very big...

03-27-2005 08:41 AM

Jack - thanks for the real world experience feed back on holding plate vs evaporator current use. I am designing an on board refrigeration system, and have always liked the idea of the storage capacity of a holding plate, and your experiences support my hunches. I have two questions for you. In my research, I have learned holding plate characteristics can vary. Plates like those from Isotherm or Frigoboat freeze down to around 12 degrees above zero farenheit, while plates like those from Technautics or E-Z Kold freeze down much lower - to minus 13 degrees farenheit. First question: in your findings of 55-60amp/hrs vs 30-35amp/hrs, which temperature range plates were you observing? Second: with the holding plates that freeze around 12degrees above zero, has this proved adequate for a meaningful freezer space/performance - even a small one at one to two cubic feet - or is it really too close to 32degrees farenheit, and will only freeze items directly touching the plate? (R30 plus insulation is a given here). Jim D.
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