Who provides the best 12 volt refrigeration systems?

[a64pilot]

Originally Posted by john61ct

There are mains home fridges more efficient than 12V compressor portables like Engel, but not sold afaik in NA market.

While I don’t believe the Engle to be any marvel of efficiency, I doubt your statement.
Reason is to be frost free you have resistance heaters, and you heat the seals, even the outside of the box to prevent condensation, all this heating requires a significant amount of power.

[john61ct]

I'm sorry, no idea how your statement relates to mine?

Maybe you misinterpreted mine?

I was speaking generally, not wrt any particular 4x4 fridge, Engel just as one respected and pretty efficient example.

In mild weather as a fridge, 12-20AH per 24hrs.

[a64pilot]

I was saying that I don’t think many home fridges are more efficient than the portable DC one or by extension the 12VDC Marine systems. Not due to their inefficient cooling systems, but due to all the heat that is applied to keep them from condensation and frost free.
I believe if you defeated those systems, then it’s likely that You may have a very efficient system.

[john61ct]

Originally Posted by a64pilot

I was saying that I don’t think many home fridges are more efficient than the portable DC one or by extension the 12VDC Marine systems. Not due to their inefficient cooling systems, but due to all the heat that is applied to keep them from condensation and frost free.
I believe if you defeated those systems, then it’s likely that You may have a very efficient system.

I see. I dunno if the super-efficient ones even have those features.

[Richard Kollmann]

Originally Posted by a64pilot

Hysteresis is usually used to to explain play or slop in a mechanical system, as well as even electrical, it may be misused, I likely used the term.
In a mechanical system for example a throttle cable can be said to have hysteresis as its being used to both push and pull, and when you change from pushing to pulling, you have a lot of slop.

I’ll try to explain what I think the gist of Richards post was, but I’m not going to dissect it.
1. Very few if any eutectic systems are actually eutectic, a true eutectic system will freeze completely and thaw completely holding the same temp, that is largely why it’s desirable. Most systems use a mix of Glycol and water and begin freezing many degrees before they become a complete solid, if they ever become a complete solid.
2. As this non eutectic mix begins to thaw it is absorbing less and less heat, making it less and less efficient as it thaws, where it would stay closer to the same if it were a true eutectic fluid. Same as it’s freezing, it’s a less desirable storage medium, however it is spread over several degrees, not just one exact temp like a true eutectic is. Reading into what Richard has said is what give Pete’s system the ability to adjust the temp within a rage of temp, if it were a true eutectic, you really can’t adjust temps much at all without losing the eutectic’s advantages and Richard explains why, cause once frozen, the solid will absorb much, much less energy per degree of temp change. It still works, just your maintaining RPM of that flywheel as opposed to spooling it up and letting it slow down
Remember to use a mechanical explanation, the eutectic tank is a huge flywheel.
3. Once a fluid is completely frozen, it’s ability to become an energy storage medium decreases drastically, it’s the phase change that absorbs and releases the heat, way more than just mass, so if your turning the temp down past the freeze point, your losing some advantage of having a eutectic system.

Actually what Richard was doing was merely explaining in a little more technical terms the operation of a true eutectic system, and what is usually sold as a eutectic system, but he was just stating facts, however he was also explaining in technical terms, why Pete’s system works to a great extent, he explained why / how Pete’s system can have an adjustable thermostat and still function to some extent as a eutectic system, not a pure one, but a system that can take advantage of the energy storage medium of a cold plate.

Now this is my opinion, and very often people do not hear what has been said or written, we put our own spin into it, it’s human nature

a64pilot, Has the correct understanding of energy consumption on ice box conversion refrigeration using small hermetically sealed 12 volt compressors as there is no appreciable difference. The only real difference in energy consumed results from box size and volume of heat needed to be removed.
Twenty five years ago with fixed speed one size compressor and limited evaporators they always had to fit all box conversions. Manufacturers tried to convince buyers of these systems that 2 amp-hrs per hour, over 24 hours was good energy performance ignoring the all box heat loads and not the same.
Today there are many more options available to the refrigeration application engineer mainly because of the variable speed compressors and almost unlimited evaporator configurations. Frequent compressor cycling is no longer a worry. The gas volume efficiency improvement at lower compressor speeds today allowes an applications engineer to reduce daily energy consumed on a small heat load boxes by 50%.

I have nothing to sell the helpers that worked with me in refrigeration over the last thirty years have all passed away. I sold of my shop equipment and have only a few things left. Anyone who has one or more of my five books on boat refrigeration knows I favor no manufacture over another.

[Colin A]

Originally Posted by a64pilot

I was saying that I don’t think many home fridges are more efficient than the portable DC one or by extension the 12VDC Marine systems. Not due to their inefficient cooling systems, but due to all the heat that is applied to keep them from condensation and frost free.
I believe if you defeated those systems, then it’s likely that You may have a very efficient system.

It's hard to compare you would need to run a test like energy star does on the home models to a 12V model and see what happens. The Energy star test from what i read is at high ambient (90 degrees) and includes running the defroster but I don't think it includes opening and closing the door.

[john61ct]

Just to be clear I was not talking about anything available in 120V AC.

The more developed, better regulated countries like Australia, New Zealand and Europe, all are 240V markets.

The USian EPA requirements have not been pushing technology improvements for many years, the US is leaving things to the free market, so the others are far exceeding what is available here.

[skenn_ie]

Brushless DC motors make things a lot more efficient, as long as the driver electronics is good.

[a64pilot]

Originally Posted by skenn_ie

Brushless DC motors make things a lot more efficient, as long as the driver electronics is good.

I agree with this, and I suspect that the Bd type compressors are DC brushless motors, and people smarter than me can argue whether or not a Brushless motor running off of a DC power supply is actually an AC motor or not.

I don’t think 120 VAC or 240 VAC makes much difference, just I have not seen a modern home fridge that wasn’t frost free, had heated exteriors and heated gaskets, but then I’ve not really looked for quite awhile either.

I fired my compressor electronics module while ago, and seeing as how I had to replace it, I went with the new AEO module.
Now maybe it’s the placebo effect, but it seems to cool faster, have more frequent off cycles and seemingly even use slightly less power when it’s on. If you watch your amp meter, the soft start and ramp up of RPM is easily visible.
It also seems to not interfere with my HF radio, where the old one sounded like 1950’s Sci-fi space ship noises

[Colin A]

Originally Posted by john61ct

Just to be clear I was not talking about anything available in 120V AC.

The more developed, better regulated countries like Australia, New Zealand and Europe, all are 240V markets.

The USian EPA requirements have not been pushing technology improvements for many years, the US is leaving things to the free market, so the others are far exceeding what is available here.

It's interesting some have gotten better here. Looks like a 24% improvements from 2001 to 2014 for the most efficient models. I know in the RV world the big bus conversions have been going all elcetric (no propane), and they have played with fridges. I had one tell me they tested 12V fridge vs a home unit on the inverter and found the power consumption to be almost identical and the cost was way less.



Of course the RV 12 v units aren't all that efficient.

[a64pilot]

Originally Posted by Colin A

It's hard to compare you would need to run a test like energy star does on the home models to a 12V model and see what happens. The Energy star test from what i read is at high ambient (90 degrees) and includes running the defroster but I don't think it includes opening and closing the door.

I think if you could find out what the duty cycle and the current draw when on, you could get a real good idea of efficiency.
If you know anyone who has one, just plug it into a Kill-A-Watt Meter and it will tell you exactly its power consumption over a 24 hour period. You know how many AH your boat system uses, convert that to Watt hours. Then you would know.

[Richard Kollmann]

Originally Posted by skenn_ie

Brushless DC motors make things a lot more efficient, as long as the driver electronics is good.

Module failures excluding lightning strikes are generally a result of system designer pushing the compressor design envelope to far or installation of electrical wiring that does not comply to compressor manufacturers good practice recommendation. Low amperage devices like these controllers require clean power direct from battery. Cheap switches, circuit breaker wire terminals and improper wire for refrigerator power can also contribute to module failures.

[skenn_ie]

Originally Posted by a64pilot

I agree with this, and I suspect that the Bd type compressors are DC brushless motors, and people smarter than me can argue whether or not a Brushless motor running off of a DC power supply is actually an AC motor or not.

3-phase permanent magnet. I am doubtful that they would work well with AC but I think the distinction is voltage though. Extra-Low-Volage (ELV) is under 50V if I remember correctly.

[missourisailor]

Originally Posted by a64pilot

Bd type compressors are DC brushless motors

To the best of my knowledge, the Danfoss compressors are all 3 phase AC motors.
The control modules are just glorified inverters. Allowing the compressors to run off of DC.

I may be wrong, but I don't think there even is such thing as a brushless DC motor.

[skenn_ie]

Originally Posted by missourisailor

To the best of my knowledge, the Danfoss compressors are all 3 phase AC motors.
The control modules are just glorified inverters. Allowing the compressors to run off of DC.

I may be wrong, but I don't think there even is such thing as a brushless DC motor.

Do you mean a BLDC moter driven fridge, or generally ? BLDCMs are used in drones, model (fixed-wing) aeroplanes, cars, and in reverse, with a permanent magnet, wind generators though, then, the same device becomes a PMA. There are two styles, inrunners and outrunners. In inrunners, the rotor is inside the stator.