Author Topic: Archive 6  (Read 4098 times)

Richard

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Archive 6
« on: May 03, 2012, 10:29:28 am »

Archive 6

Selecting Refrigeration In General
It appears you have a five cubic ft box to refrigerate with unknown insulation. Battery capacity and power management will be a problem even if you upgrade the present system to high output alternator with smart regulator. Because the batteries are not fully charged when leaving the dock it will take two to three hours of engine run time, worst case, every day, even with a new alternator and doubling battery capacity. When purchasing refrigeration for your boat, do not except a general recommendation of what to buy. There are twenty manufacturers and over one hundred options to choose from, so accepting general advice of what unit your boat needs is a mistake. I have put together a slide show on my web site to help boaters avoid the mistake of selecting the wrong refrigeration system, titled, What Works and What Doesnt. at http://www.kollmann-marine.com Ounce you have decided on the level of cooling required and size and type of equipment you will add, and amount of insulation, I will be glade to recommend a couple manufactures. Lets say you want a small freezing section, Your cruising area is tropical with water temperatures above 78 Degrees and three to four people on board. In that case I would Recommend either a Adler Barbour or Frigoboat unit with a BD50 compressor. The size of bin type evaporator will depend on lid opening and box shape.

Testing the controllor?
Hi Richard, Thanks for your help on this. I have some typical resistance readings for the motor connector now and with the drawing you have kindly sent me can do some more detailed testing of the compressor. If the readings meter out to be approx the same on my compressor, is there anyway I can test the control unit with say a dummy load or some such thing? Am I better off do you think just replacing the whole thing rather than the old controller if it has in fact failed? Thanks Ray

BD Module Failures
There are three coils in these BD brushless motors a small one to count revolutions the other two are field coils. By alternating and switching a modified AC current to the field coils the armature rotates. Miller Marine is the only one I know of that will repair these units. info@millermarine.com I would repair or replace only the module unless the evaporator is showing paint bubbles and signs of corrosion.

Evaporator vs. Cold Plate Frost
Thanks Richard for all of your incredible help and information. When in your forum answers you refer to general conditions of evaporators, would it be safe to assume that these conditions would be the same for cold plates? Specfically 100% of the surface covered with frost? THANKS again.

Updated info
Hi Richard, Thanks to your drawing and some resistance figures from another source I've been able to comfirm the comprssor meters out fine (with a good meter). 0.2 ohms for each winding and the tacho reads 3.4 ohms, nothing shorted to ground. I opened up the controller again and tested the transistors again, don't know what I was doing before as they are both the same type. I found 1 has a juction shorted and a crack in the case, never a good sign with transistors in my experience :) I was wondering if transistor failure typically damages other components in the unit. Also I think I read in one of the forum posts you knew part numbers for compatable transistors I could replace them with, was this correct? Thanks again for your help. Regards Ray

Determining refrigerator Performance
The short answer to the question, are there visual performance indications between Plates and thin plate evaporators? Answer, it will depend on system and component design differences. All refrigerants absorb heat from an evaporator and there are several types of evaporators used in boat refrigeration: Thin plate evaporators: where tubing is imbedded in thin metal plates. Today these are generally made of aluminum and referred to as Roll-Bond evaporators. These thin plate evaporators offer the best refrigerant heat absorbing performance in small refrigeration systems. Holding plate evaporators: contain a liquid solution around the refrigerant coil that freezes storing energy mush the same as a battery. The solution volume in a holding plate determines the energy stored. The only advantage of a holding plate is that it stores energy. The disadvantage of a holding plate as an evaporator is it is slow to absorb heat in area to be refrigerated. unless a holding plates surface area is larger than the normal size thin plate evaporator. Plate evaporators: are less than one inch thick and are of three types, Copper evaporator tubing fixed to the back of a stainless cover, tubing sealed to a stainless or aluminum cover incorporating a heat sink past (thermo conductive compound) or a holding plate with solution inside of less than one inch thick. Fan evaporator: that are much like todays home refrigerator but without a self defrost feature. Great application for coolers where temperatures are between 40 to 60 degrees F. At colder temperatures fan evaporator coils must be defrosted after each compressor run. On thin plate evaporators it will be the refrigerant frost line that determines correct amount of refrigerant. On these small capillary tube systems the exact amount of amperage and frost line is a good measuring stick of overall performance. Cycling time On and Off on fixed speed compressors will indicate performance change but never compare cycle times against another system or boat. On the newer variable speed compressors cycle times may not have a bearing on performance as slowing compressor speed may improve efficiency. Large holding plate systems should all use thermostatically control expansion valves with a storage tank (receiver) to handle and store changes in refrigerant volume. A slight glass will provide an indication of refrigerant volume generally clear no bubbles when holding plate is completely frozen. There are many systems where the sight glass will not be full of liquid and bubbles even when plate is frozen. Frost line on large holding plate systems is controlled by the expansion valve and frost will start to show on plate surfaces where refrigerant tubing coils contact it. A combination of suction pressure readings, sight glass liquid and compressor run time is what is necessary to judge a large holding plate systems performance. Refrigerator pre cruise check list you dont need a mechanic to check out your boats 12 volt refrigerator before your cruise Dont for get to clean the condenser coil annually on air and water cooled refrigerators. Turn the refrigerator on and after 30 minutes there should be frost covering the evaporator. The system is functioning correctly if there is a thin layer, or more of frost covering the complete surface form top to bottom. An area not covered with frost indicates a loss of refrigerant or a performance problem. Frost on return line back toward compressor means too much refrigerant. Large refrigeration system check out. Large refrigeration systems in boats generally have holding plates inside the refrigerated box that may take more than an hour to freeze. A touch of a finger on different parts of the system can tell if the system is working OK. On the line just before the plate is an expansion valve, by touching the outlet of this valve performance of the system can be determined. After about ten minutes the temperature of the outlet of this valve should be below +10 degrees F., If you place a finger on the valve outlet at this time your finger will almost stick to the valve indicating the system is probably OK.

frigoboat conversion
6 cuft (divided in middle) cooled by aircooled AB compressor & box style evaporator no active spillover system. In the Bahamas this spring averaged 85 amphr/day. Performance - evaporator side good, other side too warm. I have a 140 amp alternator and a kiss wind generator, 800 amp hour bat bank. Will probably add 175 watts of solar. In 18+ average winds the kiss could handle the load but that did not happen often enough. I have been encouraged to explor the Frigoboat water cooled (no pump) system with L shaped evaporator and their larger compressor(variable speed) and a spillover thermostatically controlled fan. I am concerned if this works well in tropics. will it have problems in cooler waters (boat's home port is in Maine). If this conversion is a bad idea, I am open to suggestions for different approaches.

Module Transistors
The only information I have on module transistors only applies to the first generation module this is the one where the fuse holder screws into the front face of heat sink. On some of the first Danfoss modules there were two large power transistors mounted in the heat sink face. These transistors are the motor choppers and can not be purchased from Danfoss or Motorola. Here are two direct replacements bolt on transistors, wire up and dont forget the heat sink grease. NTE/ECG (249) or (251), RCA (SK 9440) or (SK 3858).

Knowing when to upgrade
If you can live with 85 amp-hrs per day in tropical conditions and the refrigeration unit produces the cooling results you want I can not see any advantage in buying a new unit. If the Adler Barbour was installed correctly, and the condenser coil is free of dirt and dust, and the refrigerant level is correct you might see a three to six amp-hr per day reduction by installing a Keel Cooler unit. The new speed controlled compressors do offer energy efficiency for boats in cool climates or when boxes are smaller than six cubic feet.

Problems with Danfoss unit also
Hi Richard, I am having almost the same exact problem with a "cold machine" on our boat. It immediately blows the fuse when powered up. I have a pair of them. Of course the one that is on the fritz is the one that has lousy access. The other one is very accessible and working fine. Figures.. Could you please email me the same info you mentioned so I can check mine out. Does the white plug on the side of the compressor just pry out? I didn't try to tear into the module because I didn't have any info on what it should meter out at. Was just standing on my head tonight trying to figure this out. Mine is also the DB25 Danfoss unit. 1990 vintage. Guess I can't complain. I bought your book on refrigeration a few years ago at the Melborne SSCA get-together, but I don't see this information included in it. Thanks for all the help you provide, Steve steve@dorado-construction.com Tampa, FL

So many options for evacuation - which is best??
Hi Richard, I'm very close to charging/leak detection now installing a refer/freezer system with 1/2hp AC compressor. Your book has been worth its weight in gold in helping me choose the right insulation and getting the install right. I have a question regarding evacuation of the system: There are a few ways available to do this: 1) Buy a vacuum pump and pump it down 2) Use the compressor itself to pump it down 3) Blow R-134a through the system with the suction line open, blasting out the air and moisture The Technicold manual that came with the unit suggests purging the sytem via #3 above. It mentions this is every bit as good as using a vacuum pump. I plan to do this, since it's less expensive. Do you think this would be a good idea? Is it the "right way" of doing it? Will it remove all moisture and replace it with R-134a? Thanks in advance. I'm almost done, and don't want to make any stupid mistakes. Plus... we have a charter at the end of next week, so I'm under the gun to do it right. Take Care, Capt Sean

Dehydrating water from refrigerant
A little bit of air left in a refrigeration system may reduce the systems capacity slightly; too much air raises the pressure. When moisture is left in the refrigerant circuit it can causes premature compressor failure. Water, oil and refrigerant react together to form acid and sludge. Two things happen when acid travels through a system copper is absorbed and electroplated on metal parts in compressor and acid in refrigerant of hermetically sealed electric compressors over time will destroys the insulation on motor windings. If an electric compressor is cooled adequately and the oil is acid free history shows it will last twenty to thirty years. I believe dehydration with a refrigeration vacuum pump is an important step. Have you checked with a local tool rental store? A one day refrigerant vacuum pump rental should only cost $20. From 1983 to 1995 until the new regulation came out banning venting of refrigerants I did recommend purging when a vacuum pump was not available but my designs did include double filter/dryers. Using the refrigeration compressor itself to evacuate a system will remove the air but only the moisture suspended in the air. To properly dehydrate by boiling and change water droplets to a gas it takes warm temperatures and a vacuum of 300 or less microns. The problem with 134a and Ester oil the oil does not want to give up the moisture in it.

Wow..
Wow, Richard. Excellent advice, as always. I was completely unaware of the venting law, since my refrigerator is older than 1995. It suggests the venting method. I will look into renting a pump - another great idea! Thanks a bunch. Anyone who is reading this thread and didn't buy his book... DO SO NOW! :) Capt Sean