Norcold 12 v fridge

[AZSpyder]

The temperature will change the run time. This is why I referred to it as a variable. Since it as 70 degrees when I tested it I only know how it does at 70 degrees. The battery would be for night and actually I'm not even planning on camping where it is 80 degrees or more at night.

I don't know where the 50 amp hours came from. My number aren't estimates. They are measured values even if only at 70 degrees. If uses 1.5 amps an hour and it ran for 24 hours it would be 36 amps. I don't expect to have to run it 24 hours without a charge. Most of the stops would be overnighters while traveling. I'm thinking maybe 12 hours parked. Now it is 18 amp hours to recharge. It will charge up when under way again. Since it would need daily support if off the grid for an extended time a 60 to 80 watt solar panel should be able to keep it up. That would depend on the weather and time of year, a couple more variables.

Still that is not a 24 hour discharge. On battery at night and on solar panel or tow vehicle charging system during the day. Actually most of our camping will be at sites with hookup and showers. A group 27 deep cycle should fit my mission profile just fine with allowances for the variables.

[eamarquardt]

The temperature will change the run time. This is why I referred to it as a variable. Since it as 70 degrees when I tested it I only know how it does at 70 degrees. The battery would be for night and actually I'm not even planning on camping where it is 80 degrees or more at night.
I don't know where the 50 amp hours came from. My number aren't estimates. They are measured values even if only at 70 degrees. If uses 1.5 amps an hour and it ran for 24 hours it would be 36 amps. I don't expect to have to run it 24 hours without a charge. Most of the stops would be overnighters while traveling. I'm thinking maybe 12 hours parked. Now it is 18 amp hours to recharge. It will charge up when under way again. Since it would need daily support if off the grid for an extended time a 60 to 80 watt solar panel should be able to keep it up. That would depend on the weather and time of year, a couple more variables.

Still that is not a 24 hour discharge. On battery at night and on solar panel or tow vehicle charging system during the day. Actually most of our camping will be at sites with hookup and showers. A group 27 deep cycle should fit my mission profile just fine with allowances for the variables.

You present a number of assumptions/variables/conditions in the above statement (I put them in bold just to be clear) that weren't included in any of your other posts. I factored in my belief that the 70F ambient temperature you cited as the basis for amp/hour load is very conservative for most places during the summer months. But if you're only using the battery at night it may be in the ballpark. Not knowing you only intended to run on battery power at night I factored up 25% (80F average ambient temp) and at this average temp I'd expect your load or amp/hours will probably go up 25% or more. If your 36 amp/hours increases 25% that's 45 and I rounded off to 50 because that's half (the max recommended discharge) of a 100 amp/hour battery. Close nuf. Some of the variable you cite are beyond my ability to concieve: ie: on the road for 12 hours a day. I have a hard time driving 3 or 4.

Sounds like you have it all worked out and I agree if you drive 12 hours a day and always have "shore power" at campgrounds you'll do OK. Having lived off the grid while sailing, my experience tells me that without shore power and driving 12 hours a day you are pushing the envelope.

I wasn't criticizing you, just hoping to share my experiences.

Cheers,

Gus

[AZSpyder]

The intent of my post was to document the test results of a current check on one particular refrigerator. Since then I realized some of the higher then advertised current draw is a fan that came with it now looks like a Norcold option and would be added into the basic 3.1 amp advertised.

The loading should be based as much as possible on reality. Unless you have some test results adding 25% for a 10 degree increase in ambient temperature seems way high. Rounding up 5 amps gave away 10% of the battery power budget. I have some 1 amp dome lights and sure would not give away 5 amps.

You simply don't have enough data to attempt my budget calculations. Something that must be kept in mind is the operating envelope. I never said I would be driving 12 hours. A traveling day may not even be 24 hours. Then there are stops for gas, lunch (out of the handy refrigerator) and rest. Any changes of the expected design envelope will have to be taken into consideration. You also don't know the loads besides the refrigerator or the battery selection.

I personally track the power as close as possible. Note the refrigerator data I posted was to 1/10 amp, I was actually reading it in 1/100 amp. I do electrical loading analysis at work also but those items are better documented then items found in campers. Once you get a total then the fudge factors and be added in depending on loads that aren't fully documented and keeping battery lifetime degradation in mind.

[eamarquardt]

We're bickering but then again I love a good bicker!

I think your assumpition of an average outside ambient temp of 70F is a pipe dream for a summer day. You live in Tucson. Here's what Wikapedia has to say about your temperatures:

The temperature doesn't even dip to your assumed 70F during the summer months so I don't think your assumption is correct for your area for summer operations(I like to plan for worst case situations).

There are those that will certainly argue that I don't know, well, beans. However, I know enough to ask those that do before I post. I checked with my resource for matters pertaining to heat transfer. A PhD in Engineering, UCLA, ME, Rocket Scientist (35 years at Rocketdyne) who specializes in, you guessed it, HEAT TRANSFER. He assured me than if you raise the temperature differential between the inside of the reefer and the outside XX% the power required to cool the inside of the reefer will go up pretty much XX% as at the temperatures we're talking about the curve is pretty linear. So if your inside temp is 35F and your assumed outside temp is 70F that's a difference of 35F. If the average temp is 80F (more realistic IMHO) this is a 28% increase and you can expect your electical consumption to go up 28%. I'm not an engineer by training, but I do understand the physics involved and can do basic calculations regarding heat transfer.

I also think that measuring the current down to the nearest .01 of an amp will not yield results that are any more statistically significant than measuring it to .1 amp.

Everything in life is a compromise. Absorption units lose effeciency as the heat increases. Electric compressors are realative power hogs. Most crusing sailors avoid them like the plague and use holdover plates with an engine driven compressor.

In my last post I agreed that you had a plan, you know how you plan to use the system and manage your battery power better than I, and I was comfortable with that.

But, I stand by my thoughts that I think your assumption of an ambient temp of 70F is optomistic at best and your power consumption calculations are therefore optomistic.

I'll be quiet now and try to ignore the pain and go back to sleep (the great escape from neuropathic pain!).

Cheers,

Gus

[AZSpyder]

You still don't know how I intend to operate and you still think you know the environment it will operated in! Yes I live in Tucson and I know quite well what the summer temperatures are. I don't know if you have realized that these campers can be connected to a car or truck and moved for some distance. I have no intention of camping where I live. During that same time there are places that have cooler temperatures then Tucson. In the mountains at the edge of town temps would be in the 50s and 60s at the camp grounds.

I am still not buying the 25% power increase per 10 degree change without proof. I am not going to camp off the grid in anyplace that has 80 degree nights! I don't really give a rats a@@ what the temperature in Tucson is at night or the imaginary efficiency of a refrigerator at 80 degrees because I won't be there.

If the 25% is accurate it may be a good thing. Like is said I won't be camping with 80 degree nights but could be with 50 or 60 degrees or less. This would substantially extend the battery budget but I'm not going to guess at it. I haven't found the data and am interested if you have it.

[eamarquardt]

Each time you post, you share more of how you intend to operate your reefer. In your last post you shared that you plan on camping in the mountains with much cooler temperatures. If I had known as much as you, my thoughts would be different but I only know what you share.

The amount of heat transfer (conduction) is directly proportional to the difference in temperatures between the two areas one is concerned with (radiation of heat is different). So if your inside temp is 35F and your assumed outside temp is 70F that's a difference of 35F. If the average temp is 80F (more realistic IMHO) this is a 28% increase and you can expect your electical consumption to go up 28%. Simply because if 28% more energy is getting into the reefer, it will require pretty much 28% more energy to pump it out. Not a difficult concept, IMHO. YOU are RIGHT, if you go somewhere where it is cooler than 70F your energy use will go down, a good thing IMHO.

My source (in addition to what I have learned (in physics in HS and college) is a PhD in Engineering from one of the top schools in the nation (UCLA), has been a bona fide rocket scientist at Rocketdyne for the past 35 years, and he SPECIALIZES in HEAT TRANSFER with sophisticated computer models. I'm beginning to think that you believe the world is flat and that you discount the germ theory of disease (as does my former doctor, ha), HA!

I have conceded the point (several times) that you know better how you intend to manage your energy better than I and you also know the enviornment that you will be operating better than I.

Check out this web site:

http://hyperphysics.phy-astr.gsu.edu/hb ... tcond.html

If you have something to refute my logic and the second law of thermodynamics (that Congress has yet to amend, ha), other than your disbelief, I'm all ears.

I'm merely trying to share what I know, but as it seems it isn't what you want to hear, you are rejecting it.

Fine.

Gus, OUT!

[AZSpyder]

I work in a world of facts derived from test results. Theoretical designs do not perform exactly as calculated in the real world. Reality is what keeps the environmental test laboratories in business. This is especially if laws are ignored. Even in the design stage of a refrigerator there are more laws that may have been enacted after your attended school, such as the second law of thermodynamics. I think the main influences not account for are the basic laws and principles of simple machines such as energy transfer.

Electric motors change efficiency with temperature changes. This can not be predicted without detailed design data of the motor. Even then it is theoretical. The reality comes from environmental testing. Compressors change efficiency with temperature changes too.

Fact, I ever said I refute any of the laws of thermodynamics. I said I would like to see test reports supporting a 25% current increase with a 10 degree change.

It is unlikely I will be able to find environmental test results for a RV part. I did find some test data on a small DC compressor refrigerator for the medical field.
http://fridgefreeze.com/performance1

The test data was a bit of a surprise since it is not linear. I guess that pesky thermodynamics is acting up.

The basic DC current results with changes in ambient are:
From 70 to 85 degrees a 13% change or 8.66% average per 10 degrees.
From 85 to 100 degrees a 23% change or 15% average per 10 degrees.
From 100 to 115 degrees a 18% change or 12% average per 10 degrees.

Note the efficiency is improving in the high end over the mid level test. Not linear and not over 15% for 10 degrees. The 70 to 85 range I may experience is under 10%.

Like electrical load analysis everything must be taken into account, even all the laws of physics but that is just a start point. The bottom line is test results.

[eamarquardt]

I don't believe in:
Santa Claus
The Tooth Fairy
EPA Mileage Ratings and
The unsustantiated claims of people trying to separate me from my wife's money (she works, I don't, therefore she considers it all HER money).

Call me a cynic!

http://fridgefreeze.com/performance1

Is the web site of a company that would like to sell us their product. They probably are testing with an empty reefer (no energy required to cool food down, like replenishing your cold beer supply) and not losing any cold air by opening the door. Their "test results" are probably slanted to sell their product, just like the claims of the costs of operating electric cars and the power produced by solar panels.

Therefore, I take what they say with multiple grains of salt!

I consulted with the "Rocket Scientist" again. My assertions about the heat gain are correct. With the inside temp at 40F outside temp 70F as our baseline with an outside temp of 80F the heat gain goes up 33%.

However, he went on to explain, a good compressor system will move three watts of heat energy for about 1 watt of electrical energy. This is why "heat pumps" are more efficient than resistance heaters (within certain temperature constraints). So this accounts for the current increase reported on the web site cited above being less than I expected and was advocating.

YOU ARE RIGHT-only empirical testing under real operating conditions will PROVE how effective these dc units are. Me, I'm gonna stick with what cruising sailors have practiced based upon their (and my) experience-minimize load. Because the effectiveness of absorption units decreases with higher ambient temperatures a compressor unit may be a better choice if you can feed its appetite for juice. I'll have to try my gas unit when the temperature heats up and see how it performs.

So, as you seem to have the reefer and test equipment, get out there, do some testing under real world conditions (making ice, cooling food, and opening the door in a normal manner) and tell us what you experience as far as the real amp hours required to run these things.

I LOVE A GOOD "BICKER" AS I AND SOMETIMES OTHERS SOMETIMES LEARN A THING OR TWO. I'm now waiting for your real world results so I can learn some more.

For the third time, I think you have a plan and will get what you want out of your system with some "shore power" or solar panels.

Cheers,

Gus

[eamarquardt]

Rumors and feelings to the contrary my intent when posting is to share my real world experiences, hear the thoughts and experiences of others, and get to the "bottom of things".

This string has been interesting. However, after a long conversation with Dr. von Arx (the mad Swiss Rocket Scientist just retired, this week, after 35 years of being a heat transfer specialist at Rocketdyne and now a part time professor at Cal. St. U. Northridge) I am not convinced of some of the "facts" presented in this string.

If an internal temp of the reefer is 40F and an outside temp is 70F is our baseline, then if the outside temp goes to 85F, 50% more heat will be conducted into the inside of the reefer, period, end of discussion. The laws of physic make it so, period! One would expect that the "run time" of the cooling mechanism would have to go up by 50% to remove this additonal heat. In additon since the condensor is now having to dump this heat into air that is warmer (the external temp) the transfer would not be as efficient. Thus you have two factor working against you. These, to some of us, are pretty intuitive conclusions.

However, being open to all explanations, I called J. Black (I'm not sure if J means Jay or it's just J) at Fridgefreeze. Although I thought I was speaking to the "land down under", Fridgefreeze is really in San Diego. J (or Jay) was very friendly, knowledgeable, and shared my enthusiasm for sailing. He developed his units for marine use and believes them to be the most efficient units on the markets. We had a nice chat and he agreed with my understanding re the laws of thermodynamics. During the conversation it came out that he uses a std commercially available compressor, uses the best insulation, and his condensor is very efficient. He also shared that in his performance figures do not account for the opening and closing of the reefer, were for steady state operations (not putting in warm food requiring a cool down), and that he wasn't able to absolutely control the ambient temperature (the tests did not take place in a test chamber under controlled conditons). He also included a 15% fudge factor (apparently I'm not the only one to include fudge factors in my calculations).

We discussed his test results and he "stands by them" and I don't doubt his honesty. I, again discussed this with Dr. von Arx in detail. It was his opinion that there might be some improvement in the overall efficiency if you happen to hit a "sweet spot" in the performance envelope of the unit and you might get performance better than you might expect. But, getting only a 10% increase in power consumption with a 50% increase in load is way outside any expected result.

For the fourth time I agree that AZSpyder can achieve satisfactory results with his system under the conditions that he's outlined. But, in general, electric reefers are power hogs.

I'd like to get my hands on one of these units and get some real experience in their performance. If the "real world" performance is as good as J (or Jay) Black suggests, I'd like to know and might consider spending some of Suzy's money on one of the Fridgefreeze units. I'd like to get it sorted out soon as I'm actually almost ready to start construction of the tear (the frame is finished) so I'd determine if I should build my tear to fit my three way (which isn't the optimum way to go as absorption units don't work well when it gets hot out) or one of the Fridgefreeze units.

I'm gonna send J (or Jay) a link to this thread. Maybe he can provide a unit for "testing" in real world conditons. Maybe Dr. von Arx would be willing to get involved (afterall he has some spare time now, but wonders how he got anything done when he had to work for a living) and "borrow" some test equipment (he must have some contacts and we could do this up "right".

Just want to get to the "bottom" of things.

Cheers,

Gus

[razorback]

Are your knickers in twist, or your panties in a wad? Come on guys.
show us individual pictures so we can determine who actually has the biggest egg head.....JUST KIDDING.........
Really though I WOULD like to know who has the biggest slide rule...
or maybe the biggest pocket protector.
again, just a touch of levity.

Larry

[eamarquardt]

Are your knickers in twist, or your panties in a wad? Come on guys.
show us individual pictures so we can determine who actually has the biggest egg head.....JUST KIDDING.........
Really though I WOULD like to know who has the biggest slide rule...
or maybe the biggest pocket protector.
again, just a touch of levity.

Larry

First, I forgot to mention that I also don't believe in the Easter Bunny!

As far as your comment about my being an "egghead", BITE ME! Just a touch of "levity", ha.

I'm too sick to let the "little stuff" irratate me, and aside from surviving a disease nicknamed the "suicide disease" it's all small stuff.

I do, however, enjoy a good exchange of ideas and have no problem admitting the fact I'm wrong, when, in fact, I am proven wrong.

Just seems that the "laws of physics/thermodynamics" (that even our legislators can't amend) are being ignored here.

Goin to Hawaii for a week next week. Only the second time away from home (in fifteen years) for more than a day or two, aside from multiple trips to Pittsburgh where the "Pro from Dover" on my condition (I hate the term disease as it implies I have "cooties" and I am "cootie free) hangs out, and multiple hospitalizations locally! I'll take my netbook and see if I can find a hotspot. If not I'll be "off the air". You gonna miss me?

Since you asked, here is a picture of me and #1 wife (Suzy, who has been recommended for Sainthood for putting up with me for over 35 years!) We were younger and I was thinner in those days! As you can see my head is definately not egg shaped (but some on the forum would argue otherwise).



Cheers,

Gus

[razorback]

Hey Gus
After looking at the picture two things are evident.
1. an egg is NOT the shape of your head.
2. You definitely married OVER your head.
Seriously
I hope the two of you have a wonderful trip to Hawaii.
I also will pray that the issue you are facing with the docs is resolved very soon.
It is a wonder I have survived this long. Can't believe I was so stupid as to say something dumb to a MARINE of all people !!!

regards
Larry

[eamarquardt]

First, I'm glad you recognize a MARINE when you see one. I once picked up a hitchhiker while in uniform (70's). He had no idea!

RE my marriage: Suzy is only 5'2" (brown eyes not blue) but can KILL and/or MAIM with one glance of the "evil eye". I did however: "Get Lucky"! On rare occasions, she also feels lucky!

Been to 250 doctors, 12 operations (including "brain surgery" and surgery with no anesthesia), all sort of meds, to no avail. Gotten several "psych" evals to refute the opinions of some arrogant and ignorant doctors that the problem isn't all "in my head" (as it really is as that's where the nerves that cause my pain are!). Lost my job and am considered fully disabled as I'm too unreliable to be employed.

The last MD that read my history was amazed that I'm: 1) Still alive 2) Still married (only cause Suzy has been nominated for sainthood) 3) Have a realtionship with my boys (had a great time on Sunday and Monday with #2 working on his Baja Bug) 4) Still trying to be productive!

I'm really not as "cranky" as some of my posts might indicate but I have a few opinions (all of them STRONG), like a good tussle (a Marine trait), and enjoy the genuine good will on the forum and will speak out when I think it is required!

Will post from Hawaii if I can find a hot spot.

Cheers,

Gus

[SurfStone]

Im gunna live offgrid for 6 months or so, and would really like to find the best 12volt freezer for my money. I will have solar and deep cycle, and will get more if needed but deffinetly need a freezer

[eamarquardt]

Im gunna live offgrid for 6 months or so, and would really like to find the best 12volt freezer for my money. I will have solar and deep cycle, and will get more if needed but deffinetly need a freezer

I think the "concensus" is that Engle is the brand to buy. For planning purposes the "duty cycle", based upon the experience of others, seems to be about 1/3 on 2/3 off depending on outside temperature.

On solar panels, again based upon the reports of others with experience, I think you can figure on about half the rated output of the panels for about 8 hours a day. The makers of panels seem to be overly optomistic with their output ratings.

Although it's a "hotly debated topic" I still think going a month on a 5 gallon propane tank is a viable alternative.

Hope this helps.

Cheers,

Gus