Fridge Loaded "Fully or Partly" Myth Debate

Submitted: Tuesday, Jul 18, 2017 at 10:12
ThreadID: 135274 Views:3391 Replies:12 FollowUps:44
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The current stable ambients were a good opportunity for me to conduct further testing on the contention of keeping a fridge packed full in order to minimise energy input.

Using appropriate instrumentation, I firstly tested the fridge empty, then loaded it fully with plastic jars full of water at a temperature setting of 4 degrees. The Ah consumption was essentially identical in each case.
The compressor duty cycle changed but the total Ah remained the same.
I then removed the upper layer of contents and repeated the test, again with the same result as before.
Then I placed several layers of bubble-wrap above the contents to fill the void and found that the Ah consumption was reduced by nearly 10% ----Eureka!!

I got to thinking hard about this. The only reason to put electrical energy into a stabilised fridge is to remove the heat ingress getting through the fridge insulation. Heat enters through the cabinet sides, bottom and top and first encounters the evaporator plates where it is absorbed before it can reach the contents. But look at those evaporator plates, they are not on the bottom or top, and at the sides they do not even reach all the way to the top. Heat is pouring in through the lid and the upper shoulders of the cabinet directly onto the contents. When I placed bubble-wrap on top of the contents I had placed further insulation in its path.
So I repositioned the bubble-wrap outside the cabinet, on top of the lid, leaving a void below the lid above the contents, and repeated the test. The result was that the Ah energy was reduced to nearly as much as when it was inside the cabinet.

So the MYTH IS BUSTED on simply keeping the fridge full to save power.
But the MYTH IS PROVEN on adding insulation between the top of the contents and the heat source.

On trips, I usually add a folded towel above depleted contents to stop bouncing but have taken no note of fridge Ah change, but it seems to have that advantage. Putting a folded towel over the lid if no room inside with it hanging down over the cabinet shoulders could be a good idea if the fridge is chockers too. In fact even a mat of that 10mm HD foam on the inside bottom could be beneficial too. Few fridges have really adequate insulation after all.

Watch for me on the ABC Science Show. lol



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Allan

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Reply By: RMD - Tuesday, Jul 18, 2017 at 11:17

Tuesday, Jul 18, 2017 at 11:17
In my Waeco, used as a freezer I have foam blocks in the end compartment ie butter area, to reduce the airgap. ALSO, I heavily insulate the Engel fridge and freezing Waeco with old sleeping bags in addition to there insulating bags around the case.
Very Mythtical isn't it?
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 18, 2017 at 12:20

Tuesday, Jul 18, 2017 at 12:20
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Hi RMD,

Adding external insulation is good I should think but I have no room for it.... the troopy is packed like a sardine can!

I'm not prepared to sacrifice my butter/cheese shelf to an insulating bricks at 35 litre I need all the space I can get. Might try wrapping the butter & cheese in some bubble-wrap though.

That "butter shelf" is interesting in the Waeco. I also run an 11 litre Waeco as a freezer positioned as a console between the front seats. To provide cool drinking water I drop a pair of stainless water bottles through holes hole-sawed in the lid to sit on that shelf. The thermodynamics work out that the fridge body remains at minus 10 degrees but the water in the bottles is just nicely chilled. A luxury!

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Allan

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Follow Up By: RMD - Tuesday, Jul 18, 2017 at 17:28

Tuesday, Jul 18, 2017 at 17:28
G'day Allan
Have you placed a "patent pending" on that? Waeco might steal the idea now you have released the intellectual property into the arena.

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RMD
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 18, 2017 at 17:43

Tuesday, Jul 18, 2017 at 17:43
. Nah, RMD. Do you have any idea of the cost and effort to lodge a patent?
Waeco are welcome to the idea.
Anyway, they probably would have as much trouble as I did to locate suitably sized drink bottles to fit in the available space. Then get a correctly sized holesaw to fit the bottles. Agrhh, wasn't easy. But was worth it for the cool drink.
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Reply By: Les - PK Ranger - Tuesday, Jul 18, 2017 at 12:13

Tuesday, Jul 18, 2017 at 12:13
Fill fridge with food and beer.
Turn it on.
Enjoy the trip.

Not much seems to affect the efficiency that much, and what does it matter ?
You just drive daily touring, or have enough solar to keep well powered.

There are just too many variables to worry about it.
Ambient temp in cab or rear tub, direction of travel (sun on fridge), putting warm cans of beer in each morning before travel, plug losing contact in ciggy plug for part of days drive (happens rarely), passenger not closing lid properly, etc etc.
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 18, 2017 at 12:36

Tuesday, Jul 18, 2017 at 12:36
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Ah Les, your a Troglodyte, lol.

I'm not troubled with worrying about variables but weren't you one of those promoting "filling the fridge" a while back. Maybe not Mate. I'm just putting a myth to rest.

But set it up right and then there are no troubles "to worry about".

You can't do much about ambient temperature, especially in a parked vehicle, but you can avoid positioning the fridge in the sun. Mine is never in the sun, it's under the bed. Fridge cannot be stowed without closing lid... it's a snug fit under ned which reliably keeps lid shut too. "Ciggy plug"??.... What do you take me for? My cable is wired in with no plug except on the fridge. Do right what you can do right and accept what you can't.

This Troopy is set-up right Les. Pop up some time and I'll give you a hand.lol



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Follow Up By: Les - PK Ranger - Tuesday, Jul 18, 2017 at 13:49

Tuesday, Jul 18, 2017 at 13:49
Lol, maybe a little more of a trog than I used to be, really the way I travel power consumption isn't a big issue.
My simple needs are the fridge and led strip light on the canopy tilt window to cook / tend bar, etc under.
The techniice fridge is very low draw, maybe when I get the Waeco 11lt setup as a freezer I'll need to solar up more if camping 2 - 3 days etc.

This matter would be a little important to many people so good on you for doing some testing etc.

I really like your cdx11 mod with the drink bottles Allan, maybe one trip up with the Ranger I'll pop up and have a look if you're in town.

I will be up there next week for a stint of work, and oh yeah, one weekender out Goomburra for a look, mate from Gold Coast in his 'cruiser and me as pax in my brothers vehicle (a Jeep Grand Cherokee, wish us luck !).
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 18, 2017 at 15:05

Tuesday, Jul 18, 2017 at 15:05
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Les, my battery needs are not great either, but I was looking for something to do and was a bit scornful of "blind beliefs". It was interesting and convincing.
And yes, it could be useful for some people.

Techniice eh? Nice. Such low draw because of the good insulation. That is really what refrigeration is all about --- insulation.

I have tried to setup to have it all work with little fussing. I want to be enjoying my environment, not running around reading gauges. I can't even be bothered with 'tracking and waypoint logging'. Digital moving maps are only to keep me from getting hopelessly lost. I have spent my life in technology and enjoyed it but now I just want to enjoy living! Even hauling the camera out is a bit of a chore for me.

That CDX11 mod has been wonderful. I abhor warm water whilst driving and rotating drink bottles through the fridge is bothersome. Takes a little courage to whack a holesaw through the lid of your fridge though. I can imagine the reaction of some.
When run as a freezer, the CDX11 'parcel shelf' is of no value for storing frozen stuff and not even room for a couple of cans I think, so it was a worthwhile adaptation.
I would be really happy to see you up here. Stuck around bored until end August when off for a few weeks which includes Hay River Track. I'm sure you have done it and could offer a few bits of advice. I'll keep my holesaw handy. lol
you can find my email in my Profile under "About Me". If unable, put your email up in a Post Followup and I'll come back.

Cheers Mate, and thanks for suffering my sophistical discourses.


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Allan

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Follow Up By: Les - PK Ranger - Tuesday, Jul 18, 2017 at 17:51

Tuesday, Jul 18, 2017 at 17:51
"the CDX11 'parcel shelf' is of no value for storing frozen stuff "

Absolutely right there Allan, and I personally feel (gut feel, fly by the seat of your pants, 'real life experience' whole ' the vibe' thing :D) that even running as a fridge at say -2c it would have very little use, but the water bottle cooler would still be very good at the higher (than freezer) temps for some drink flasks.

I think I'd do the mod, pending ali bottle are the similar standard dia, and a rubber sleeve collar (or numerous wraps of 2" cloth tape) could be placed at the correct height to seal it off fairly well.

Will catch up one day on a trip when I bring the Ranger up for a spin.
For most trips it is far more economical to beek early and fly up ($98 return this trip !!) but I do love bring the 4WD up and doing a couple of trips to areas SEQ and northern NSW.
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 18, 2017 at 22:28

Tuesday, Jul 18, 2017 at 22:28
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Actually Les, I had to shop around quite a bit to locate suitably sized SS bottles.
In order to fit within the recess of the shelf they needed to be 65mm diameter.
They are 150mm from bottom to shoulder which was ideal. They then sit almost fully within the cabinet with the shoulder still reaching the 'seal' and just sufficient protruding to easily grasp.
A piece of 2mm thick felt with snug holes acts as a seal. Works fine.
Draws only a couple of Amps as I recall and still cycles a bit at -10 degrees.
Naturally, being the freezer, it stays in service all the time.

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Allan

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Follow Up By: Les - PK Ranger - Tuesday, Jul 18, 2017 at 23:35

Tuesday, Jul 18, 2017 at 23:35
Cheers Allan, will check the dozen or so bottles I have here when ready to mod.
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Reply By: Member - Boobook - Tuesday, Jul 18, 2017 at 12:39

Tuesday, Jul 18, 2017 at 12:39
Not so fast Allan. I'm not clicking to the ABC to watch you yet.

The purpose of filling the fridge is to take up air space and keep thermal inertia for when you open and close the lid.

Try it again, opening the lid every 30 mins or so. The full one will definitely use less then. Less cold air to escape then get recooled.
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Follow Up By: CSeaJay - Tuesday, Jul 18, 2017 at 13:20

Tuesday, Jul 18, 2017 at 13:20
Allan

What Tony says is spot on.
In real life I have seen a big difference in power consumption (more power when only partially full) and it is simply because all that 'cold' is gone every time you open it.
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Follow Up By: Member - Boobook - Tuesday, Jul 18, 2017 at 13:24

Tuesday, Jul 18, 2017 at 13:24
Old wine casks work really well. You can keep blowing them up as the food level goes down. 4 or so partially filled ones are better than 1 or 2 bigger ones.
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 18, 2017 at 14:24

Tuesday, Jul 18, 2017 at 14:24
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Sorry Tony, You are wrong.

I did a bit more than I described in that post but did not include it for brevity just as I did not post a whole lot of numerical records to avoid nit-picking.

You give my professional training and experience no credit. When it comes to carrying out physical investigations, recording and analysis I will claim some reasonable experience and competence. It was part of what I did for a living. But I expected that I may have need to defend my analysis to some critics who have possibly formed beliefs without the benefit of controlled scientific study. Not however you.

In point of fact, one of the tests that I also did was to laboriously open the fridge each hour (of my waking time) remove two of the 1 litre water-filled jars, close the lid, open it again, and replace the jars, so as to simulate the practice of accessing the fridge in normal use. I found absolutely no change in the consumed Amphours! Yes, it surprised me too but there was NO detectable change. I can only conclude that the action displaced little of the chilled air and that any that was displaced and required re-cooling was of so little "thermal inertia" that it was not detectable by Ah consumption.

Furthermore, although I did not test for it, I would consider that hauling out an "inflated wine bladder" or wads of bubble-wrap to access the food (or beer) would likely displace more chilled air from the chamber anyway.

I did a few more observations too..... do you want to fire some more shots across my bow?

And CSeaJay, what does "in real life" mean? = Casual observation without controlled investigation. Most of the time such observations result only in seeing what one anticipated. I am unable to give them any credence..... but hold to your shibboleths.

Guys, I am not saying to discard your favourite ideals and habits. I performed a well-controlled scientific evaluation and posted the results. Consider them then accept or discard them as you wish but do not tell me that I am incompetent.


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Allan

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Follow Up By: Member - Boobook - Tuesday, Jul 18, 2017 at 15:20

Tuesday, Jul 18, 2017 at 15:20
I tested it extensively over 1 week Alan with the freezer set to -22. It made about 8AH difference if i opened the door every hour.

I don't want to argue about it Allan but I too have appropriate qualifications and background, and did a documented test over a long period with a watthour meter.
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 18, 2017 at 16:24

Tuesday, Jul 18, 2017 at 16:24
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I was aware of your expertise Tony which why I was surprised at your dismissal of my finding without peer recognition.

It simply goes to show that such studies are not conclusive in themselves but require scrutinised comparison and assessment. There may well be a significance in that you were running at -22 whilst I was at +4 degrees. This study was after all about the behaviour of a refrigerator, not a freezer. I would not expect a camping freezer to be opened "every hour" unless you are really into Icypoles. For our tests to be comparable we need to keep "apples to apples". No?

"8Ah difference in a week" is surely a fairly small difference especially for the total consumption of a freezer running at -22c. That is less than about 1.0%

I also used a digital integrating amphour/watthour/voltmeter. Have not tested its accuracy but would think its repeatability to be reliable. Power supply was a regulated 12.6v mains type. Environment was my garage/workshop which is within the house perimeter and fully insulated. Ambient temperatures were logged and both the actual temperature and small profile deviation was consistent with each test run.

I'm inclined to consider that your tests were in fact fairly comparable to my own but our conclusions are at some variance. In the end, I guess our audience will be the judges.

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Allan

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Follow Up By: CSeaJay - Tuesday, Jul 18, 2017 at 16:35

Tuesday, Jul 18, 2017 at 16:35
Sorry Allan for sharing my 'real life' experience without backup, but it is my experience over 25 years of camping remote and completing numerous major and remote tracks. Sorry you believe the reply to be empty of meaning. Rather than adding a follow-up here I replied further down in my own reply so as not to muddy this follow up thread which is spiralling.
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Follow Up By: Alloy c/t - Tuesday, Jul 18, 2017 at 16:54

Tuesday, Jul 18, 2017 at 16:54
Real life ? Who cares as long as the beer is in-between 2-3c and the tomatoes and lettuce is not frozen , the freezer part makes ice [for the scotch and soda] and the ice cream stays frozen ...... insulation takes up 'precious' room and the 12volt fridge brigade of manufactures con us all in actual usable internal size and then have the hide to sells 'extra' insulation....
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Follow Up By: Les - PK Ranger - Tuesday, Jul 18, 2017 at 17:45

Tuesday, Jul 18, 2017 at 17:45
Ok, that's it !!
Test documentation and / or real life experiences at 20 paces !! LOL :)
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Follow Up By: AlbyNSW - Tuesday, Jul 18, 2017 at 18:53

Tuesday, Jul 18, 2017 at 18:53
I don't think losing cold air is that big a deal when opening the door as it doesn't take a lot to heat or cool air but placing warm items of denser medium takes a lot more energy to cool down
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Follow Up By: Member - Boobook - Tuesday, Jul 18, 2017 at 19:03

Tuesday, Jul 18, 2017 at 19:03
Geez Alan take a chill pill.

Go read your posts.

Please don't be so rude and check your facts.

Forget it.
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 18, 2017 at 19:11

Tuesday, Jul 18, 2017 at 19:11
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With sincere respect, what the hell are you on about Tony?
Have I miss-spelled your name or something?
Insulted your wife?
Kicked your dog?
I honestly do not know how I have offended you.
Am I becoming unknowingly insensitive in my old age?

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Follow Up By: Michael H9 - Tuesday, Jul 18, 2017 at 19:36

Tuesday, Jul 18, 2017 at 19:36
Did somebody open the fridge door on this thread? The ambient temperature rose very quickly it seems to my untrained eye. Lol :-)
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Follow Up By: Allan B (Sunshine Coast) - Wednesday, Jul 19, 2017 at 00:12

Wednesday, Jul 19, 2017 at 00:12
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Well, that went well, didn't it Michael?
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Allan

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Reply By: Gnomey - Tuesday, Jul 18, 2017 at 12:43

Tuesday, Jul 18, 2017 at 12:43
Nice work Allan.

Cheers
Mark
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 18, 2017 at 14:25

Tuesday, Jul 18, 2017 at 14:25
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Thanks Mark.
I needed that.
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Allan

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Follow Up By: Sigmund - Wednesday, Jul 19, 2017 at 08:12

Wednesday, Jul 19, 2017 at 08:12
Yeah, data is very sexy. Good effort. It's hard work to control all the variables.

Living with a Waeco 40 l fridge I found it worthwhile to boost its insulation.
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Reply By: Frank P (NSW) - Tuesday, Jul 18, 2017 at 16:12

Tuesday, Jul 18, 2017 at 16:12
Nice little project, Allan, I will use that info in managing my car fridge.

The Vitrifrigo 130 litre van fridge is more problematic, being a front-opening cabinet type. It has a remote compressor and without breaking into the gas circuit I cannot pull it out far enough to improve side, back and top insulation.

We use storage containers the depth of each shelf to create "buckets of cold" to reduce the spill of cold air when the door is opened.

Before I converted the van to lithium batteries I was always looking to reduce 12V power consumption. I made a water cooled condenser to run in series with the conventional air and fan cooled one and had it installed to the refrigerant circuit by a fridge mechanic. Very simple - extra refrigerant line threaded through a metre of 12mm copper tube and a small pump supplying about 1 litre per minute of water from one of the van's tanks.

I got the idea from these people. My understanding from them, IIRC, is that over a given period of time water can remove about 100 times more heat than air at the same temperature. I thought that if it could be done it may reduce compressor run times.

It did. I didn't do an amp-hour test, but I did a roughly controlled before and after test of compressor duty cycles. With the van parked in the same place, with the same fridge load and the same ambient temperatures (38+C - it was an obliging Sydney heat wave:-)) the before cycle was 60% on, 40% off. The after cycle was almost the reverse - 40% on, 60% off, and that's after I wound the compressor speed down to reduce run-time current draw - 5 amps down to 3.5.

The small pump that Ozefridge supplies draws 0.5 amp and runs when the compressor runs.

Cheers



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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 18, 2017 at 17:07

Tuesday, Jul 18, 2017 at 17:07
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Interesting setup Frank. Yes, as you say, water is far better as a transfer medium because of its greater specific heat value.

Way back as an apprentice I saw ther most amazing refrigeration machine. Picture this if you can........... It comprised a hollow shaft set in bearings and supported three 400mm copper spheres along its two or three metre length.
It was mounted through a wall with one sphere inside in an insulated room and carrying fan blades on its circumference. The outermost sphere dipped into an open top tank and had some shallow paddles on its circumference. There was a belt pulley on the shaft outside which was driven by an internal combustion engine. The centre sphere contained a compressor whose crankshaft remained stationary by an off centre gravity weight whilst the compressor rotated together with the whole assembly. The outer sphere contained the condenser while the inner sphere contained the evaporator. Pipes in the hollow shaft carried the refrigerant. The whole thing was a fully sealed-unit refrigerator to cool a butcher's cool room. It was no longer in use and with the premises being redeveloped it was headed to the scrapheap!
I was fascinated by it at the time but no-one appreciated its heritage significance. I have never been able to find out more about this remarkable machine or any photo of it. Seems totally lost to any record. What a shame.
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Reply By: CSeaJay - Tuesday, Jul 18, 2017 at 16:29

Tuesday, Jul 18, 2017 at 16:29
Allan
Why is it then that out in the bush and actually camping/using the fridge I draw far more power from a partially full fridge or freezer?
Time and time again; stock up, fill her up, and the battery SOC shows a marked difference, getting worse the lower it gets, stock up again when in civilisation and voila!
Just came back from a three month trip which again confirmed my previous experience, but this time with even more controlled environments (fully charged by full day driving, setting camp in shade, steady weather conditions)
Not a 'scientific' measure by any means, but above happened time and time again, the freezer performed significantly better with a full load
Why would my experience be different to your findings?


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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 18, 2017 at 17:28

Tuesday, Jul 18, 2017 at 17:28
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Hi CseaJay,

I honestly did not consider your "reply to be empty of meaning". I simply could not comprehend its significance. My failing, not yours.

I can give you no opinion for your observations. There must of course be reasons for the behaviour you witnessed but I could not even guess them. See, that is the perilous part, making guesses without careful observation and assessment. Sometimes we have to of course in the necessity of the moment but it can result in inadequate conclusions.

I don't know why your experience would differ from my test results, but I do believe that there would be valid reasons for that difference. The usual explanation is that "We have missed something".
I will say that I do live by the view that "Whatever works, works".



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Allan

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Follow Up By: Sigmund - Wednesday, Jul 19, 2017 at 13:25

Wednesday, Jul 19, 2017 at 13:25
My limited understanding is this: SoC is a poor indicator in general of what current's been drawn and what capacity is left. At a minimum the battery needs to have had no inputs/outputs for several hours before the voltage measurement.

We can now get cheap inline power monitors that will record amps and watts, peak and total, and this is much more useful data.
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Follow Up By: Allan B (Sunshine Coast) - Wednesday, Jul 19, 2017 at 15:58

Wednesday, Jul 19, 2017 at 15:58
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Not so sure just how useful in its simple form Sigmund.

Measuring Ah in and Ah out does not reveal near the true SoC due to transfer losses. You need to put significantly more energy into a battery than you can get out again. Most of these losses are variable with such things as battery age condition, charge/discharge rates, temperature etc. so the transfer ratio will change significantly with time and event. SoC indication on solar controllers will lead you up a garden path.

Some charging systems used on battery banks such as fork-lifts have used such a system as 'charging controllers' but it was programmable for the transfer ratio and adjusted regularly. Such batteries also required a supervised 'maintenance' charge regularly to ensure good battery condition. I even now do that for my Troopy auxiliary batteries.

Voltage as a SoC indication is of some value. It gives some idea if the battery has useful SoC or is dead flat!!

Just charge the batteries with a good stage-charger and they will be filled.... reasonably so.
There is no easy way I'm afraid. Bantam has dealt with this in detail.
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Allan

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Reply By: 2517. - Tuesday, Jul 18, 2017 at 16:47

Tuesday, Jul 18, 2017 at 16:47
Hi Allan what are your thoughts on fridge bags?my neighbour who is a fridge mechanic maintain all they do is stop the frig from being knocks around and block the air circulation around frig.
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 18, 2017 at 17:36

Tuesday, Jul 18, 2017 at 17:36
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Well, I have never tried one and they are not very thick so do not afford much extra insulation. Might be of some value if the sun is shining directly onto the fridge but could only guess. Could also be of some hassle when opening and closing the fridge.
Most value is possibly in mechanical protection as your neighbour says.
Maybe some who have used them will respond with their views.
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Allan

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Reply By: Keith B2 - Wednesday, Jul 19, 2017 at 08:20

Wednesday, Jul 19, 2017 at 08:20
Interesting findings Allan. My understanding has always been that, because heat rises, most of the heat entering the fridge cabinet comes in through the floor of the unit. So I wonder what would happen if the bubble wrap was on the bottom of the fridge.
Keith
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Follow Up By: Allan B (Sunshine Coast) - Wednesday, Jul 19, 2017 at 09:01

Wednesday, Jul 19, 2017 at 09:01
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Hi Keith,

That notion of "heat rises" can cause some confusion as it is 'shorthand'.
It actually refers to the phenomenon of when fluids (air) are heated, the hotter sections of fluid lose density (become lighter) and so rise through the cooler fluid.

In solids, heat travels by migrating by conduction toward the adjacent cooler parts of the object.
So any heat applied to the bottom of the fridge (or anywhere else on the cabinet) will pass through the cabinet toward the cooler zone within the fridge. Once within the fridge, the heat will tend to 'rise' through the chamber due to heating the air in the chamber in accordance with the explanation above.

So actually, heat will enter the fridge by conduction through any wall of the cabinet and the insulation should be generally equal on all walls. In point of fact, the upper surfaces of the fridge are perhaps more likely to be heated from solar radiation so maybe they should enjoy enhanced insulation or shielding. Which is why I suggest a folded towel or similar draped over the lid if it is exposed to solar heat. Even better would be some foil-coated insulation with reflective properties.
But any extra insulation, anywhere on a fridge, is good.




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Allan

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Follow Up By: Keith B2 - Wednesday, Jul 19, 2017 at 11:36

Wednesday, Jul 19, 2017 at 11:36
I am building a little off road caravan out of composite and was planning to put a eutectic fridge kit into a cabinet of my own design. The refrigeration outfit who were to supply the gear recommended that the floor of the fridge be double the thickness of the roof for freezers and 30% thicker for fridges. Ozefridge

"For refrigerators we suggest a minimum of 75mm thickness of refrigeration grade urethane for walls and 100mm for the base. For freezers we suggest 100 mm for walls and 150mm for the base."

I decided to go for one of the new Evakool 210 litre units instead.
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Follow Up By: Allan B (Sunshine Coast) - Wednesday, Jul 19, 2017 at 13:10

Wednesday, Jul 19, 2017 at 13:10
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Keith, dunno why they would have recommended that. There may be good reason or they may just think so!!! If I were incorporating that into my considerations I would be asking them why?
I could guess at some reasons like maybe the fridge sitting on the floor whilst the sides are comfortably enclosed within a cabinet or their design exposes more heat gain at the bottom of the appliance, but who knows. I learned (the hard way) long ago, don't just assume but if it concerns you, find out... ask.

Eutectic fridges assuredly have certain advantages but they are not the "Magic Bullet" that some may suppose. Essentially they utilise the Phase Change of a medium to obtain thermal carry-over storage. This enables the fridge to operate on cycles to suit the available input energy such as when solar power is abundant. It can also enable a more efficient operation of the refridgeration cycle. However, it comes at the the increased cost of manufacture (and sale!!) and of cabinet size. They have their place in the market, particularly medical, and If you want Rolls Royce then go for it.

Yeah, never used an EverKool but their locally manufactured models have a good reputation. Yachtsmen pay homage to their iceboxes.

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Allan

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Follow Up By: Allan B (Sunshine Coast) - Wednesday, Jul 19, 2017 at 16:36

Wednesday, Jul 19, 2017 at 16:36
Keith,

Well I DID ask, or at least, looked.

On Ozefridges website I found their explanation as follows.......

"For refrigerators we suggest a minimum of 75mm thickness of refrigeration grade urethane for walls and 100mm for the base. For freezers we suggest 100 mm for walls and 150mm for the base. (Heat rises as it attempts to penetrate the insulation therefore the base is most important and the top least important assuming it is not in direct sunlight.)"

There is the old "heat rises" mantra again. And it is being misapplied possibly to suit their reasoning. Actually, it doesn't 'rise' at all. What happens is that in a fluid filled void (even including the Earth's atmosphere) as heat is applied the lower portion of warm fluid becomes less dense and cannot support the cooler more dense 'heavier' fluid above. Gravity and hydrostatic effects then act to cause the heavier cooler fluid to 'sink' and the warmer fluid is displaced upwards. It warmer fluid does not actually 'rise' of its own accord.
Note that if heat is applied only at the top, the warmer fluid will remain at the top and no displacement occurs.
In a fridge, this effect and action results in the bottom of the fridge to become cooler than at the top. We have all observed that.
The bottom of the fridge now has a greater differential temperature with the outside of the cabinet and will suffer greater relative losses than the rest of the chamber walls. There is some sense to applying more insulation where the losses are greatest.
It is possible that this may be the reason for Ozefridge to recommend more insulation on the bottom. But they may not wish to declare that.

Incidentally, this process continues whilst ever heat is gained into the cabinet and is usually countered by such as recirculating fans. Or stack your beer on the bottom.

Cheers
Allan

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Reply By: 9900Eagle - Wednesday, Jul 19, 2017 at 10:25

Wednesday, Jul 19, 2017 at 10:25
Alan, thanks for sharing your findings and I have always believed it made very little difference if any at all.

I had a look on the net and found this info.

Full versus empty
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Follow Up By: Allan B (Sunshine Coast) - Wednesday, Jul 19, 2017 at 11:57

Wednesday, Jul 19, 2017 at 11:57
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Hi Eagle,

Your link was interesting and thankfully mirrored my conclusions.

Not an easy discourse to follow however as it represents as a "Physics" scientific site and uses terms and symbols perhaps unfamiliar to laymen yet mixes in "real-world" expressions that muddy the water. It is posing as "academic" yet aimed at an untaught audience. The sensible answer is in there and ultimately comes out however.

I dislike the terms "Real World" or "In practical terms". In physics, there is no difference between 'scientific' and 'practical' behaviour (leaving aside 'theoretical' or 'speculative' study) Practical behaviour obeys the scientific explanation. What does differ is only bits that are disregarded for convenience or simplicity , but that can also confuse the reader. It is surely best discussed entirely in scientific terms or in "practical" terms. In this regard, people such as the venerable Julius Sumner Miller and Karl Kruszelnicki of the ABC Science Show do the public a great service....... physics that are correct but understandable.

Apart from that 'spray' I found your link to be a good contribution. Thank you eagle.
Cheers
Allan

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Follow Up By: 9900Eagle - Wednesday, Jul 19, 2017 at 15:05

Wednesday, Jul 19, 2017 at 15:05
Alan, I just ignored all the feel good prose and went straight o the layman's answer so it didn't hurt my head.
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Reply By: member - mazcan - Wednesday, Jul 19, 2017 at 10:59

Wednesday, Jul 19, 2017 at 10:59
hi Alan B
an interesting read
i previously owned a very old s/h 29lt engel grey sides with lite green lid
it kept things cold and was very reliable but I decided I may be able to improve its ability so while I had it completely stripped down and apart for a restoration job on it to get rid of rust as it use to be owned by a fisherman and had been on a boat most of the time
I decided to dismantle the lid there wasnt much installation in it so I put in as many sheets of polystyrene and alternative sheets of thick alfoil until I was only just able to clip the lid back together
I also removed the freezer unit from the box and did likewise sides and bottom then reassembled it
the difference was astounding if I turned it up just above 2 on the fridge setting I was freezing and busting stubbies of beer and cool drinks and the milk was also solid
I had to run it on 1 from then on so learnt from that experience that it is simply all about the thickness and quality of the insulation that makes a fridge highly efficient
I had previously pulled the outside cover of a rheem gas water heater and wrapped the tank in thick insulation which greatly reduced the gas consumption by keeping the heat in and reducing the burner time and my gas bill
that heater was installed at my current house in october 1989 and is still working perfectly by changing the anti corrosion rod regularly and running the house on mainly rain water and I also wrapped the copper pipes in the ceiling with insulation tubes as well I get almost instant hot water even in winter
plumbers have told me its the oldest rheem heater they know of all the others have died long ago
so once again its all about the insulation for hot or cold and so that's what prompted me to try and better the old engels performance I sold the 29lt 4 yrs ago and upgraded to a 40ltr but I have to turn it up to high readings compared to the old one but they have made it impossible to get the lid etc apart on the newer models but i would like to better it too
cheers
AnswerID: 612614

Follow Up By: Allan B (Sunshine Coast) - Wednesday, Jul 19, 2017 at 12:38

Wednesday, Jul 19, 2017 at 12:38
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Hi Mazcan,

Yes, in thermal economy, insulation is everything.
Just think of it, given sufficient highly effective insulation, you would never lose any cold, errrr rather, you would never gain any heat, in a refrigerator.
However that of course is not sensible when considering practicalities and economics of manufacture and purchase. Compromises are necessary in most things.

There are some camping fridges available with much superior insulation but they are larger (for a given capacity) and considerably more costly. Lesser brands are endeavouring to prune every last cent from their manufacturing cost for profit and market competition. It seems in product marketing there is little favour for the middle ground..... it is either the Greatest or the Cheapest and those looking for a comfortable balanced product are left out. It was not always so. We are then left with the recourse of adapting to suit our purposes as you have done.

Quite some years ago, before portable fridges, I chose to build my own icebox. I used a nice solid rectangular poly tote box enclosed in a cabinet of Masonite construction and well painted. The all round insulation was some black commercial foam stuff that I scrounged somehow (not styrofoam) about 65mm thick. That damn icebox kept ice in it for a week! Don't know what happened to it... I seem to have left a lot of things in my wake! Probably loaned it to a mate.......!!! But it sure demonstrated the value of good insulation.

On the subject of hot water conservation, Our kitchen and bathroom are a little way from the HWS (heat pump type). Not too far for a shower etc. but it does take a little time and wastage of hot water to obtain just a small dose. So I disconnected from the HWS at these basin outlets and fitted under-bench 10 litre water heaters. We now have instant hot water at tap and do not leave a line of hot water decaying in the roof. I have no idea of the economics of it but the convenience is just great. My wife loves it and "A Happy Wife etc....."

The only thing that still confounds me is that signature of "quebbambiddybumtal".
Oh please email me with its meaning.
Cheers
Allan

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Reply By: The Bantam - Wednesday, Jul 19, 2017 at 14:27

Wednesday, Jul 19, 2017 at 14:27
Interesing observations ...... and realy to be expected.

Given no other inputs, the only thing a change in contents is going to do to a fridge is change its duty cycle ..... that alone may be a small benifit.

THE main issue with these and other fridges is insulation ....... apart from the eskies with a tacked on fridge units all the 12 volt fridges have piss poor insulation

If you feel the outside of your fridge and it is cool to touch it is leaking heat. .... yeh now pick it up and feel the bottom.

If the fridge is direct on a ute tray or on the floor of a vehicle, putting some sort of insulation under it can make a very big difference ...... I pretty much always travel with a large folded towel on to of my fridge or esky.

As for these fridge covers ...... yes they will offer a small insulation improvement ...... but consider the temperatures involved ........ if you wore it as a jumper would it keep you warm at -2C,

for significant insulation you need at least 3/4 to an inch of good insulating material to do a worthwhile job.

Having the fridge or esky inside an airconditioned vehicle will make a dramatic difference in performance as will ensuring that the fridge has a clear path to exchange air from the fridge unit.

There is a big difference between chest and front opening fridges ....... with a front opener all the cold air falls out every time the door is opened ...... a chest type retains a lot of it's cold air even if the top is left open indefinitely, this is how supermarkets get away with open top freezers

There is also a great difference between when running a given unit as a fridge and a freezer ....... losses that may not be significant are multiplied many times when the cavity temperature is dropped 20 degrees.

even the losses in items removed and replaced increases dramatically.

And yeh good fridge or esky managment can make a great deal of difference.

if you want to extend your run time from 2 days to 4 you will need everything going for you.
If you are dependent on ice .... good managment will get you ya 3 or 4 days ...... poor managment and the same esky and the same materials will be lucky to last a day.

cheers
AnswerID: 612617

Follow Up By: Member - graeme W (WA) - Saturday, Jul 22, 2017 at 16:47

Saturday, Jul 22, 2017 at 16:47
Hi Bantum. Not sure they all have piss poor insulation, have a look at Margarets trailblazers. My new one has 3inch insulation and bd50 compressor. In 30degree ambiant the other day it took 8 mins to get to minus 16 and had not got to the cut in again of minus 6 after an hour .It draws 6 amps but its all about total power use in my situation. Never been able to understand why people buy cheap fridges. Wish someone would do a comparison test disregarding price on 12 volt fridges , I know which one would win.
cheers Graeme.
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Follow Up By: The Bantam - Saturday, Jul 22, 2017 at 21:50

Saturday, Jul 22, 2017 at 21:50
The Trailblazers are hardly a high volume mass market fridge
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Follow Up By: GREG T11 - Saturday, Jul 22, 2017 at 21:51

Saturday, Jul 22, 2017 at 21:51
The simple answer to why people by "cheap" fridges is some people can't justify outlaying $1500 + for something they use maybe 4 weeks in a year. However I do agree with you on the Trailblazers, very good for what they are , but the idea of portable is stretching it . They are big and heavy so not really an option for everyone.

My brother has one he bought second hand in 1997 to go around Oz. Wife and two kids and no second battery and knowing him no specific wiring to run it. Never heard any dramas but he would have been on the move after 2 days max.

He probably paid $1200-1500 back then and would get $900ish for it now maybe so pretty good resale. Maybe I might have first dibs at it when we sort our needs out in a couple of years, but one thing is certain it would be a reasonably permanent fixture in the vehicle.
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Follow Up By: Member - graeme W (WA) - Saturday, Jul 22, 2017 at 22:38

Saturday, Jul 22, 2017 at 22:38
Cheers Guys. Just making a point really, my latest aquistion cost 2300 so about double the cost or a bit less than say a wacoe. By the time you replace the thermister in the wacoe not if but when it stuffs up at about 400 bucks and if you are lucky and nothing else fails, the fact that the trailblazer will use half the power or better and is not that much heavier or bigger for a given size, they should be a mass seller. Replacement cost of a thermostat in mine is about 15 bucks and 10 minutes. Mine will pass on to the kids in perfect working order whatever the year is.
Cheers Graeme
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Reply By: Member - Outback Gazz - Wednesday, Jul 19, 2017 at 17:17

Wednesday, Jul 19, 2017 at 17:17
And I've been making the mistake of putting beer and food in my two fridges and heading bush enjoying myself for the last 35 years without realizing I've been doing it all wrong !

Looks like I will have to print off all the posts in this thread, do some reading and some more research and hopefully I will get it right before I get too much older lol


Happy and safe travels
( with either full or half full fridges )

Cheers

Gazz
AnswerID: 612621

Follow Up By: Michael H9 - Wednesday, Jul 19, 2017 at 17:55

Wednesday, Jul 19, 2017 at 17:55
It's always better to have a half full fridge than a half empty one. :-)
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Follow Up By: Allan B (Sunshine Coast) - Wednesday, Jul 19, 2017 at 18:09

Wednesday, Jul 19, 2017 at 18:09
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Gazz,

What's this nonsense of putting food into your fridge??????? ( obligatory lol )

Cheers
Allan

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Follow Up By: Member - Outback Gazz - Wednesday, Jul 19, 2017 at 18:46

Wednesday, Jul 19, 2017 at 18:46
G'day Allan

First of all, I thought your post was very good, very thorough, very interesting and a great read and enjoyed the "Mythbuster" result !!

re: food now, with 110 litres of fridge space I have worked out ( not as accurately as you would have ) that I can get 120 cans of my favorite beer along with 20 chump chops in my fridges so if I hold myself back to six cans a day I know I can travel for twenty days without re-supplying !! On more remote trips I take an extra 14 cans but only 10 chops which I cut in half.

There's only ever been a problem once with this set up - and that's when the wife came on her first and oddly enough last trip hahahaha lol lol


All the best

Outback "and just open the fridge" Gazz



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Follow Up By: Allan B (Sunshine Coast) - Wednesday, Jul 19, 2017 at 18:52

Wednesday, Jul 19, 2017 at 18:52
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On'yer Gazz,

110 litres? Geez I have to get by with 35 + 11 (food goes in the11)

The Bush wouldn't be the same without blokes like you! Lol

Cheers
Allan

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