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Old 17-01-2013, 19:38   #16
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Re: Plan ahead and reduce boat refrigerator down time and repair osts

Help with "Reverse Power Technology" ? That's still gibberish to be, I've never heard the phrase before.

Voltage switches, on the other hand, I'm familiar with. But a cheap switch with high/low operations and unspecified parameter as to what it would be switching, that's awfully vague. I don't see what you're trying to supply power to, I thought the controllers and compressors only cared if there was power on or off?
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Old 18-01-2013, 05:27   #17
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Re: Plan ahead and reduce boat refrigerator down time and repair osts

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Originally Posted by gettinthere View Post
As to the AEO, it SEEMED to run more often after the engine drive ran. That would seem counter to what you'd think should happen and there are a million variables. I don't have any way of quantifying this, and I could very well be imagining things. Got to stop eating those mushrooms!
After cooling by engine drive, the AEO may be running longer, but at slower speeds using less amps overall.

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Old 18-01-2013, 09:33   #18
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Re: Plan ahead and reduce boat refrigerator down time and repair osts

hellosailor, Maybe you had a different background in electrical “reverse power technology” originally taught applied to mechanical devices called reverse current relays. As this technology advanced as you indicated Diode and Zorbs replaced the more completed mechanical devices. If this is still gibberish to you I give up.



gettinthere, and colemj, After thinking about how Danfoss AEO works I can see how it becomes confused and begins to first long cycles before it short cycles 12 volt compressor ON AND OFF after engine drive compressor runs.

Engine drive compressors almost always are used to freeze holdover eutectic plates. Normal engine compressor run time to freeze plates is one hour. Most engine drive compressors are not controlled by a temperature controlled thermostat, they are turned on and off by a manual timer or return gas temperature/pressure.


Danfoss BD compressors are all cycled ON and OFF by a thermostat. The AEO function when added is not directly aware of box or plate temperatures it controls compressor speed based on how often thermostat stops and restarts compressor.
When power is first applied to compressor it will start at very low speed to protect compressor then over the next 48 minutes speed will slowly increase to its maximum speed OR until thermostat stops compressor. This ramp up speed is 9.4 Rpm per minute. On the next restart compressor will start up at 300 rpm less than where it stopped then each following cycle by thermostat increase or decrease compressor run time until optimum energy efficiency is reached. In other words when compressor is running it slowly increases speed and then when re-stated it looses 300 rpm.

My theory is in the case of a hybrid system with both engine drive and 12/24 volt Danfoss BD variable speed AEO equipped compressor system is; the AEO will reboot itself not being able to read temperature and start compressor at slow speed. When Danfoss’s thermostat teaches its preset temperature regardless of holding plate or box temperature compressor speed will be reduced by 300 Rpm.
In any case AEO is going to be manage energy consumption as best it can with most of the work done when engine drive is used.
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Old 18-01-2013, 10:16   #19
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Re: Plan ahead and reduce boat refrigerator down time and repair osts

"Maybe you had a different background"
Apparently so, Richard. When I tried a quick web search for "Reverse Power Technology" it came back with zilch. Then again, when I first read Jules Verne and tried to find out what "fuming azotic acid" was, no one had heard of that either.
Times and terms change so quickly.
A reverse current relay sounds to be simply a special case of a relay, with perhaps two balanced coils to make it function as a voltage comparator? That would count as clever steampunk engineering these days. By the time I was being taught about these things (voltage comparators) there were ICs being used for the purpose. Outside of the generator industry...nope, never met one.

Interesting ("curiouser and curiouser, said Alice") programming that is being applied to those compressors. I have no idea of why they would make it so complicated (in the name of energy savings??) but it makes me think of BMW and Audi. Very cleverly engineered, but sometimes that just makes them high-strung and full of new failure modes. A Willys Jeep didn't need sensors to monitor the sensors, much less have a hundred of anything hooked up in it, except maybe the total parts count for the engine.

Given the popularity of the Danfoss units and the, ah, questions about the controllers, it would seem that a complete plug-n-play aftermarket replacement would be the best solution. Improve the logic, improve the sensors, make it more robust. To a large extent "a board is a board" these days, and having an entire new module made up might be nearly the same price as trying to patch the existing one with "extras". That also allows one for microprocessor to decide how to run it, based on temperature, or charging sources, or ambient daylight, or any other criteria at the same time. Of course that would be a risky business proposition, since Danforth and others could easily change their design and knock a third-party out of the market, if you came up with something that worked better than what they have.

It could just be the problem is poor technicians doing the installs, in a way that leads to overheat problems. After all, gen-you-whine factory trained AC techs routinely send something like 1/2 of perfectly good AC compressors back to car manufacturers every year. That's a 50% failure rate on diagnostics, and boat techs? Why would they be any better?
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Old 18-01-2013, 11:47   #20
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Re: Plan ahead and reduce boat refrigerator down time and repair osts

hellosailor, Even though we rarely agree, your way with words always makes for entertaining reading. I think that, sometimes, our disagreements are a matter of symantics and most of the time on your refusal to accept proven, established, engineering practices. I would like to suggest that you might want to consider cancelling your subscription to Popular Mechanics.
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Old 24-01-2013, 12:41   #21
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Re: Plan ahead and reduce boat refrigerator down time and repair osts

Richard, you are the best. Thanks for all the advise you give this community!

One question: Why is the LED optional on Danfoss BD compressors? I mean, how much would it cost them to package the right LED with the compressor, so we can solder on a couple of wires and get the diagnostic information you are talking about? Or better yet, how about separate male spade connectors on the side of the control unit for that application, PLUS an LED in the box?
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Old 24-01-2013, 13:38   #22
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Re: Plan ahead and reduce boat refrigerator down time and repair osts

Akka, welcome to planet Earth. The usual answer to questions like that is "We don't want unauthoried persons tampering with our systems, so we don't include it for consumers. Our authoried service technicians just hook it up during service."

In other words, they prefer not to include it, because that also ensures the technicians will be called and will have a stronger revenue stream. And, it prevents some tampering.

Omitting a part and the installation of that part might save a buck in manufacturing, which could translate into saving five bucks off the end price to the consumer, and that's also a much more important issue than you might think.

Spade connectors? Now you've really blown the budget.<G>

One might suggest a piezo beeper instead of an LED, so that if there is a malfunction it attracts attention as well as indicating the fault. LEDs are useless at getting attention, when the equipment is mounted in a locker.
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Old 24-01-2013, 14:49   #23
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Re: Plan ahead and reduce boat refrigerator down time and repair osts

Service techs are parts changers until proven otherwise. I'm constantly amazed at techs that don't know fluke about a meter or a wiring diagram, let alone the refrigeration cycle. I'm sure you all see similar
Engineers, on the other hand, think everything looks good on paper.
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Old 24-01-2013, 15:50   #24
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Re: Plan ahead and reduce boat refrigerator down time and repair osts

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Originally Posted by familycruisers View Post
Service techs are parts changers until proven otherwise. I'm constantly amazed at techs that don't know fluke about a meter or a wiring diagram, let alone the refrigeration cycle. I'm sure you all see similar
Engineers, on the other hand, think everything looks good on paper.
Today 21:49familycruisers
familycruiser, many times you are correct. This week I was contacted by a boater with a system problem, refrigerator would not run. Serviceman remove refrigerant and dehydrated unit and re-servicing it. Reason tech gave for doing this was compressor would not run. Tech did not know that when Danfoss BD compressors one day will not run it is because of an electrical problem and has nothing to do with refrigerant flow or blockage.
If compressor runs and there is little or no cooling then problem is with refrigerant.

The reason I was contacted was the next day compressor again would not run.
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Old 24-01-2013, 16:10   #25
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Re: Plan ahead and reduce boat refrigerator down time and repair osts

You know what I use to always hear and would get under my skin. "Oh, you were just a little low on refrigerant." Like it's not a sealed system unless you have a leak, which should then be fixed. So why did you put two pounds in and not fix a supposed leak. Hacks everywhere.
So you then have to re weight the gas, as well say fix the real problem, ie blocked coil, or what have you.
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Old 30-01-2013, 14:34   #26
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We were on a mooring for a month and did not run the engine drive. The AED kept the box at about 21d. Yesterday we motored and ran the engine drive compressor for an hour. It drove the temp down lower than the 20 degrees we had been stabilized at. Now the 12 volt system is keeping the temp at 19d. We never saw 19 while moored and relying on the 12 volt system only. It seems that running the engine drive has caused the AED to lower its 'expectation' of what is the proper level and so run more often.

These temps are not from the cold plate probe but from the other probe located in the center of the freezer. Freezer is very full.
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Old 30-01-2013, 17:54   #27
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Re: Plan ahead and reduce boat refrigerator down time and repair osts

Twelve volt Danfoss refrigerator box temperature will depend on how long compressor runs. Thermostat controls how long compressor runs. If evaporator can handle all the capacity of 12 volt compressor box temperature could reach -24 degrees. What also may occur is an equilibrium between box’s heat load and system capacity.

Box temperature with engine driven refrigeration is controlled by freeze point of eutectic solution after compressor stops running, or the size of holdover plate or plates. If engine compressor were to run longer after all solution is frozen less than only 20 minutes of additional energy would be stores in plates. When solution is all frozen it contains approximately 144 Btu per pound and energy stored after solution is all solid only ½ btu per pound per degree is stored in the ice.
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Old 30-01-2013, 18:16   #28
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Re: Plan ahead and reduce boat refrigerator down time and repair osts

19 degrees seem very warm for a freezer? I would think you need 0-10 deg for long-term storage.
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Old 30-01-2013, 18:39   #29
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Re: Plan ahead and reduce boat refrigerator down time and repair osts

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19 degrees seem very warm for a freezer? I would think you need 0-10 deg for long-term storage.
We can't set the...



...temp much colder than 22 deg for the freezer section of our box before it starts freezing items in the rest of the box. So far that has been no problem. We will use items in the box in less than a month anyway so no long term storage like we have at home in our freezer where we buy items on sale to use much later.

More on the complete box build and install here...

Endeavour 37 Interion Mods Index

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Old 30-01-2013, 19:24   #30
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Re: Plan ahead and reduce boat refrigerator down time and repair osts

I have keep pork and shrimp for over 9 months in my previous boats onboard Danfoss powered/ air cooled freezer.
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