KBWaldron
Solar Enthusiast
The newer 120/240 inverter fridges do not have that same large initial current surge.
best fridge set up ?
- Thread starter davehop
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Stupid Monkey
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- Dec 14, 2019
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but, at least in the UK, are the same sort of prices as large DC fridge or fridge/freezers
The 2 Inverter fridges I saw for sale in the US (linked to earlier in this thread, I think) were pretty pricey as well.
I'm not sure what DC fridges you compared to, or how you are comparing (most of the common chest style 12/24/120v compressor fridges generally consume between 15-30 Wh/hr @ 65f-85f (18-30c) temps.
Maybe I am misunderstanding your math or your units (we should be talking in watt hours not amps), but best I can tell from what you wrote, in the winter your fridge consumes 0.7A x 120V = 84 Whr/hr and if you account for inverter losses your fridge consumes 1.55a x 120v = 186 Wh/hr? If so your fridge consumes 6-12x more energy than an efficient chest style DC compressor fridge when accounting for inverter losses (which you should when comparing AC to DC). On the other hand your $60 fridge is also roughly 6-12x cheaper, so I suppose it depends what your priorities are.
Where are you getting these figures? Mine come from occasional individual reports over 8-10 years. 30wh would be typical for those temps. 15wh would be typical in cooler weather for an medium to large 12v chest fridge.
1.55A x 12v not 120v. You measure off a shunt or an amp clamp at the battery as I stated originally.
So without inverter the fridge itself consumes about 8-9wh. Which confirms all principles of thermodynamics and electricity...theres no free energy and 12v is fundementally inefficient.
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There is a lot of information available on these chest style fridges (you call them 12v but technically most are 12vdc/24vdc/120vac). There are probably at least a hundred owner reports for the various models in various conditions on the expeditionportal.com forum, a handful of articles in overland journal comparing the different DC fridges, as well as various tests people, and organizations, have done. Here is the data from one such test (73-78f ambient, 32f fridge temp, 24 hr consumption of 276-360 Wh). You can also find datasheets from the fridge manufacturers themselves (or the compressor manufacturer--danfoss in most cases) which will tell you current draw (but not duty cycle obviously).
I must've missed that in your original comment. How did you isolate the fridge from inverter overhead if you are measuring off the shunt at the battery?
Can you link to this fridge. If you truly have a $60 fridge that uses 8-9Wh in real world conditions we should all probably be buying it, as it is somehow twice as efficient as high efficiency DC compressor fridges, and 3x as efficient as the smallest energy star rated 120v dorm fridges (such as this one). Why doesn't any data from energy star or the manufacturers themselves reflect the numbers you observed?
According to energy star, the low end (more efficient) of the spectrum for a 1.6cu dorm fridge is around 24 Wh / hr.
Yes ive seen all of the data sheets. I also used real world meaurements and online audits from other sources. The summer consumption with say a 45l unit is generally about 45A +/-.
By subtracting the idle current from the total current with fridge running.
All reports show the same across all models. It would be more prudent for you to post results of dorm fridges showing something different. I have literally never had anyone find a drastically different result.
I can see you're skeptical to which I say GREAT. I been posting about this for a long time but we are a species that has robots on mars while still fighting wars over whos caveman god is better.
We have this irrational perception that age equals wisdom in this country. We see the pitfalls of this constantly from flat earthers to static universes to even lead batteries. People who were new listened to the older folks for fridge advice, the next generation did the same and so on. Except the solar market was turned upside down in the past decade. Its now utterly irrational goven the price per watt to even try to worry about 1-5% efficiencies, if any at all, and then pay a differential that now equals 400% solar production differences.
Fridge consumption has many variables. For instance these measurements likely assume a typical 72f inner room. In a van or camper it can be quite a bit lower. I only use heat around 45-50f personally. Energy ratings are generally max draw and real world measurements often lower on most if not all appliances. My TV and computer are the same.
Thats pretty common knowledge in case you didnt know. Why actual real world energy audits are much more valuble.
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Deeply skeptical, and I don't mean to be rude, Its just that your numbers are drastically lower than what the manufacturers reports, what energy star reports, and what I have seen others dorm fridge owners report. Even among dorm fridge owners making the same argument as you (the efficiency gains don't justify the added cost when you could put that money towards panels/battery) I haven't come across anyone claiming a dorm fridge actually consumes less than a chest fridge, or claiming they only consume 1/3 of what energy star test data shows.
Could you link to the fridge you own?
Idle draw, and conversion efficiency are separate factors are they not?
I haven't come across such a comparison, dorm fridges are cheap consumer products plugged into walls, as such there isn't much testing to be found, All I've found is energy star testing, and anecdotal experiences like yours that vary wildly (yours being the absolute lowest claim I've heard for any type or size of fridge).
If you know of any comparison tests, please share them, I would be curious to see a true comparison under standardized test conditions.
First, I want to say that for many situations I agree with you here. If you are not space constrained, saving money on the fridge and adding more panels and battery capacity, is a sensible route to take.
But remember you are in the vehicle subforum. Space is often the primary bottleneck in this context. Maybe it doesn't matter in your case, but for many vehicle and marine builds efficiency is very important. Especially considering that in many builds, the fridge is by far the largest power consumer, and often their is only roof space for a couple hundred watts of PV. A 20% power savings could mean an extra day of autonomy. Ignoring space constraints in the mobile forum ignores the fundamental design challenge of vehicle builds.
Yes sometimes colder, just as often hotter (or more often). Especially in a mobile/solar application, where a heat source is much more likely than air conditioning. Either way, 72f is a reasonable baseline for testing and most of the testing I've seen for chest style fridges has been conducted between 68-85, so the ambient temp is relatively comparable and if anything favors consumer energy star tested fridges.
I'm not sure how much you know about energy star testing but you can't logically say energy star tests fridges at 72f and simultaneously say they test at max draw (which they don't--they approximate real world usage). A fridge's duty cycle is determined (mostly) by ambient temperature relative to thermostat, there is no way even the shittiest fridges would be anywhere near 100% duty cycle at 72f. And unlike with your TV and computer (where an assumption has to be made in how many hours per day they will be used, and how they will be used), a fridge's consumption will be based mostly on environmental variables not usage patterns--much easier to measure consistently and predictably.
Setting aside the fact that I don't actually think this is common knowledge, you just got through chastising people for accepting common knowledge/conventional wisdom. It seems strange to rely on it here.
Agreed. If they are conducted properly, and reported accurately and honestly real world comparisons are valuable, if you have come across any real world tests comparing dorm fridges with chest style DC fridges let me know, I would be very curious to see a direct comparison
As skeptical as I am of accuracy of the numbers you observed, I would like you to be right, A $60 dollar fridge sipping 8-9 Wh / hr, sounds amazing in comparison to a $350-1200 chest fridge consuming 15-30 Wh /hr, or a dorm fridge consuming 25-40 Wh / hr. And I would be happy to save a few hundred dollars when I get around to buying a fridge.
Theres a reason no one is using 12v appliances in a home. A reason commercial air conditioners arent 12v or even 120v. What you should be skeptical of is a claim that running little 12v compressors are somehow drastically more efficient.
Nothing 12v is efficient. What were really talking about is inverter inefficiency. Its your average line from the "old timers" especially on rv living forums. I can almost bet youve done a lot of looking or talking over there. No offense intended, many of us have. But inefficiency of an inverter is moot if youre doing an audit on the 12v side of the inverter and often over stated as a canard to disuade 120v usage. Youre not concerned about anything else than what is drawn from the battery. What is drawn is 4.27A. Thats what the fridges compressor is taking from the battery. How often it cycles will give you the WH.
Nothing else matters. That is the actual measured current. Now if you have never looked at you 120v appliances then measured their actual draw to see theyre almost always much lower, IDK what to tell you other than get your self several measuring instruments and get to investigating.
Ive shown my measurements here several times if you go and search. As well others have testified to their dorm fridges consumption.
The model is haier 1.6cu ft - its current draw is ~4.3A after 30 seconds
Idle current with lifepo4 @ ~13v general.
Fridge on
Now you dont know the duty cycle. So lets play; If we assume a 20 minute cycle we have 18wh. If we assume a 50% duty cycle which we know is fairly extreme for any fridge we get 28wh consumption. If we assume a 100% duty cycle we have 56wh consumption.
I know what the duty cycle is. Its usually about 5m30s x 2-3 per hour give or take in extreme weather differentials.
Nothing 12v is efficient. What were really talking about is inverter inefficiency. Its your average line from the "old timers" especially on rv living forums. I can almost bet youve done a lot of looking or talking over there. No offense intended, many of us have. But inefficiency of an inverter is moot if youre doing an audit on the 12v side of the inverter and often over stated as a canard to disuade 120v usage. Youre not concerned about anything else than what is drawn from the battery. What is drawn is 4.27A. Thats what the fridges compressor is taking from the battery. How often it cycles will give you the WH.
Nothing else matters. That is the actual measured current. Now if you have never looked at you 120v appliances then measured their actual draw to see theyre almost always much lower, IDK what to tell you other than get your self several measuring instruments and get to investigating.
Ive shown my measurements here several times if you go and search. As well others have testified to their dorm fridges consumption.
The model is haier 1.6cu ft - its current draw is ~4.3A after 30 seconds
Idle current with lifepo4 @ ~13v general.
Fridge on
Now you dont know the duty cycle. So lets play; If we assume a 20 minute cycle we have 18wh. If we assume a 50% duty cycle which we know is fairly extreme for any fridge we get 28wh consumption. If we assume a 100% duty cycle we have 56wh consumption.
I know what the duty cycle is. Its usually about 5m30s x 2-3 per hour give or take in extreme weather differentials.
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I'm not sure anyone is claiming that--at least I'm not. My objection is to your claim that your dorm fridge is drastically more efficient than DC chest fridges. My understanding--from everything I'm seen from peoples' first hand experiences (apart from yours) with dorm fridges and with chest style DC fridges, from manufacturer supplied data, and from energy star data--is that chest style compressor fridges are usually marginally more efficient, before accounting for inverter losses, and significantly more efficient after accounting for inverter losses ( ~15-35% more efficient). You are hung up on voltage, but there are many other important factors that effect the efficiency of a fridge. Build quality, insulation, operating parameters, design goals, will all influence efficiency.
Largely yes, this is the biggest factor by far--All other things equal--but all other things are not always equal. Dorm fridges are mostly destined for dorms, offices, hotel rooms, environments where low cost is more important than every last watt of efficiency, they are usually not built with the same design goals as DC compressor fridges.
Don't own an RV and never frequented RV forums, I also am not in the habit of blindly trusting 'old timers' advice as you keep insinuating. You are arguing with a straw man, if you keep referring back to 'old timers' and 'flat earthers.' I've tried my best to convey that my impression is based on the data i've seen from a variety of sources including owner reports, tests, anecdotal experiences and manufacturer and energy star data. From your perspective you trust your own experience and data, I get that, I would too. But from my perspective, your experience is one datapoint among many I've come across and its an outlier (admittedly I find it hard to find actual data on mini fridges most people that own them don't test or don't know how to test). I'm not discounting your experience but also not giving it more weight than 1 datapoint among many. Many of the tests I've seen have been much more systematic in testing and reporting, than the data you've shared so far. Almost none of which had anything to do with comparing AC dorm fridges with chest style DC fridges so people weren't out to prove a point.
I suppose I'll search for that data if you don't want to post your test parameters and results here, as your reported consumption contradicts all the other reports I've seen here and elsewhere. Can you point to any other data
I agree, it makes no sense when comparing between AC and DC not to include inverter losses in the calculation. The only reason we are discussing it is because your previous comments referenced numbers that didn't account for inverter losses.
It also makes little sense to reference instantaneous current draw as opposed to total consumption over a period of ideally >24 hrs. Estimating duty cycle is a step in the right direction, but measuring consumption over a longer period of time 24hrs+ would give me more confidence in the results. Seeing your data over a period of time, and with stated environmental conditions, would go a long way towards helping me trust your findings (obviously you have no obligation or incentive to convince me of anything-- but if you want to share, I would be curious to see, and maybe learn something new).
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Since you keep saying this I will try to break it down for you better.
IF youre trying to figure out what the fridge pulls in theory, you have to include the inverter. Say you took a killawatt meter reading. Then you have to include the inverter inefficiency to see what it will pull from the battery.
HOWEVER when you meaure at the battery itself that INCLUDES the inverter. For example my fridge might be pulling 3.5A before inverter. The inverter might add .8A giving a total of 4.3A.
Is that making sense for you? Inverter loss is INCLUDED.
I just gave you the compressor draw. If a fridge were designed with such a small compressor as to have unusually high duty cycle it wouldnt get very far on the market. You can safely infer most fridge design is based around 10-30% duty cycle.
Too large of a compressor is a waste and not economical overhead wise, too small of one wouldnt be able to keep up in hot weather.
In 12hrs between sunset and sunrise I generally use about 40-45Ah this time of year. That includes 1.2A idle current, 6-8hrs of TV (2a), phone, lights, water pump. And of course fridge.
Theyre $60-80 and have a return policy. Go pick one up and test it....another major reason to use one.
None?
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I understand the measurement. You don't need to explain it to me. I'm referring to all the places you say things like "So without inverter the fridge itself consumes about 8-9wh." and "My cheap $60 dorm fridge consumes about .7A at this time of year. 4.27A @ 17% duty cycle. Making it about 2x more efficient than anything 12v Ive ever seen."
Inferring duty cycle is not a very accurate or scientific way to measure something. The different between a 10% duty cycle and a 30% duty cycle is huge, and 10-30 is a tight range even you travel to areas with temperature extremes. Duty cycle is dependent on how much work the compressor must do, the greater the differential between ambient and thermostat temp, the more work the fridge will do and the longer the duty cycle.
This is exactly why testing should be long term, to smooth out the effect of any single factor and to better represent real world usage. Otherwise you are just providing a snapshot in time with no context.
As for the variables you mentioned, I'm not sure I understand how insulation would change over 24 hrs, the easy solution to stock is just to leave it untouched for 24 hours, and as for temperature either allow for normal temperature fluctuation since this represents real world conditions and state the temperature range in your findings, or test in a climate controlled environment as the test results I provided did.
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Why is that confusing? Again you measure the idle then measure the compressor to lnow what the inverter is using vs the fridge. Not that complicated.
It wouldnt but the ambient temp might. If it has really well or really poor insulation the differential can be wildly different with temp swings, especially comparing to other makes.
Like I said fridge design has a general duty cycle window. We know the vast majority of them arent going to run 1 minute or 50 minutes.
But again even if it cycles 100% the cost of the fridge vs a DC native vs the cost of solar still swings comfortably in its favor....DC has already lost any way you swing it.
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Lets put it like this
$75 fridge with 100% duty cycle = 4.3a x 24hrs x 13v = 1,342wh
45L DC compressor unit = 300wh
For a difference of 1,042wh
1,042wh / 5hrs of sun = 208w
Solar $.85 per watt or $170 + $75 fridge + $30 inverter (which is what im using) = $ 275
Vs
40-50L 12v $350-650
The absolute inarguable worst case scenario still makes DC chest fridges more expensive. So now your compiled months long audit is moot.
$75 fridge with 100% duty cycle = 4.3a x 24hrs x 13v = 1,342wh
45L DC compressor unit = 300wh
For a difference of 1,042wh
1,042wh / 5hrs of sun = 208w
Solar $.85 per watt or $170 + $75 fridge + $30 inverter (which is what im using) = $ 275
Vs
40-50L 12v $350-650
The absolute inarguable worst case scenario still makes DC chest fridges more expensive. So now your compiled months long audit is moot.
You'll find no disagreement by me on this point. Refer back to what I said earlier:
We are in agreement that the economics favor a $60 dorm fridge by leaps and bounds. The cheapest 12/24/120 compressor fridges are about $350 and the most expensive are over 3x that expensive. If cost is your #1 concern dorm fridge (or converted chest freezer) is a good choice. And even if efficiency is a concern, it may not be a big enough concern to justify the price difference, especially if you can add more solar or battery capacity.
You are looking at this way too simplistically. Looking at different designs based on different design parameters as 'winning' and 'losing' is way to oversimplistic and dogmatic. They are different products with different design goals. Going back to what I said earlier:
If you are solar rich, don't lose sleep over efficiency, if you are solar poor, efficiency counts
True...except we arent anywhere near 100% IRL
A realistic max would be 1/3 (with an actual more like 1/4) of that which translates to about real world 20w panel or a tilt mount. And if anyone is that space limited they should have aux charging anyway as solar simply doesnt work in absolutes, obviously.
A realistic max would be 1/3 (with an actual more like 1/4) of that which translates to about real world 20w panel or a tilt mount. And if anyone is that space limited they should have aux charging anyway as solar simply doesnt work in absolutes, obviously.
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Will you pair please talk about the same thing
A dorm fridge is an upright fridge just like your house fridge freezer
A chest fridge opens at the top ,hence like a treasure chest.
Also please stop destroying a valuable thread with your bickering.
Newts.
A dorm fridge is an upright fridge just like your house fridge freezer
A chest fridge opens at the top ,hence like a treasure chest.
Also please stop destroying a valuable thread with your bickering.
Newts.
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