Actual Fridge Power Draws

[Pilotamis]

I'm attempting to guesstimate my total power needs for our family when we move FT into our FWC and I can't figure out what a fridge will draw. Dometic states "Energy Consumption 12VDC (Ambient@90F, Internal@41F) 0.85 Ah/h" which I believed to be, on average we can expect under those conditions to draw .85A per hr, for 24 hrs giving us a total of 20.4Ah per day. ARB is similar with their similar sized 63QT drawing .89Ah/H for a total daily consumption of 21.36Ah per day. SnoMaster and Engle are a bit different in the way they show their data. Snomaster states "Running Current: 2.5, 5 or Variable @ 12 V DC, average run time 12 hours in 24" which I took to mean that they use 2.5Ah on low and 5.0A/h on high for 12 hrs per day giving us a total power draw of 30Ah/60Ah of use per day. That's a ridiculous difference between Snomaster and Dometic/ARB. All of which are reported as similar units. Looking online and reading a few threads the ARB and Dometic numbers appear way to low. How low are they though? What are some real world numbers that I can use to plug into a calculator and try to figure out how much power I'm going to draw at minimum. I realize that that everyone will be different. Some people are in there all the time, while others are just twice a day, but 21.36Ah vs. 60Ah makes me think I'm not reading one of their spec sheets properly.

 

[DaveInDenver]

I'd just measure what the compressor draws while running and get your own observed data for duty cycle in your installation and use.

My 11 year old Engel MT45 draws 2.2 A running and in midday I see as much as 50% duty cycle. But I turn my fridge off at night if possible (which is typical) and so my equivalent duty cycle is 25% to 33%. I happen to use 17.5 A-hr for estimating consumption in my setup, which is based on years of actual use.

 

[LivinDaDream]

The 4.2 cu.ft refrigerator in my camper is not one of the portable types that you're looking at, but very likely uses the same Danfoss type compressor. I have a power monitor attached to it at the 12V input and have been monitoring power usage in a variety of different conditions since I got it. If I stay out of it most of the day other than breakfast, lunch and dinnertime, I'll typically use around 400 watthours/day (400Wh/13.3V=30Ah per day or about 1.25Ah/Hr). The spec's indicate 3.78A power draw at 12V nominal when running and I've found that to be very accurate, though it starts out a bit higher than that when the compressor first kicks on. Duty cycle seems to be about 25% overnight and around 30-35% during the day, depending on ambient and how often I get in it. I typically cold beer/wine/water on ice in a cooler that's good for almost a week before needing replenishment with ice. I can't imagine a 60Ah use by one of those type units unless they're using some other cooling method.

Based on the data I've gathered over the time I've had it, I budget a worst case of 500 watthours per day, but I've never run that high. My 100Ah LiFePo4 battery is good for 3 days without any additional power source, if I'm careful about power consumption, though I've got enough solar that I never really worry about that, even with a few cloudy days.

Here is a link to a cheap, but very useful power monitor for sorting out your power usage. Easy to install and you can log your actual usage over time. This one handles up to 20A load, but there is another one that's identical except for using an external shunt that is rated for up to 100A loads. Data is your friend when it comes to this stuff!

bayite DC 6.5-100V 0-20A LCD Display Digital Ammeter Voltmeter Multimeter Current Voltage Power Energy Battery Monitor Amperage Meter Gauge with Built-in Shunt: Amazon.com: Tools & Home Improvement

bayite DC 6.5-100V 0-20A LCD Display Digital Ammeter Voltmeter Multimeter Current Voltage Power Energy Battery Monitor Amperage Meter Gauge with Built-in Shunt: Amazon.com: Tools & Home Improvement

www.amazon.com

Cheers!

 

[jonyjoe101]

I had an edgestar fp430, in 24 hours when set to 40 degrees it used 26ah. I measured it with a dc wattmeter. That was about 5 years ago, maybe the newer 12 volt fridges have improved more in the meantime. That was in the summer in the back of my van when I took the readings.

 

[67cj5]

I have just finished Extensive Testing of the ARB 47L / 50Qt and the power figures in most conditions are a lot less that ARB Quote

I have the ARB 47L / 50Qt and I just bought the ARB 78L / 82Qt,

Testing,

My first test was to see how long one of my 115Amp Deep Cycle Batteries would last with the Battery Cut Off set to High, The out come was hours turned in to Days and in the end I shut it down after 6 days 8 hours, purely so as not to take the battery down too far and it was still above 12v.

I also tested it on 240v and it uses 225w per 24 hour period =9.3 watts per hour when set to 4c and depending on the Ambient Temp it will use 241 watts when set to 2c, I tested it for weeks and It used very little power on AC,

This past couple of days I have had the ARB hooked up to the 12v battery again and running it through a Power Analyzer and for the last 24 hours it has been averaging 0.398 Amps per hour to 0.404 amps per hour, Over a 24 hour period, Power wise, ARB use the leased power out of all the brands, This pic was at the 24 hr mark, And they use very little watts as the other picture shows,

I am still testing it and am at the 26 hour mark now, but anyway heres the pic and watch this video to the end because ARB fridges use a lot less power than quoted. CLICK on those pictures below and you will be able to see them properly, Ok.

Hope that helps,

 

[Pilotamis]

Thanks for the replies. 67CJ5 that’s exactly what I was hoping to learn. Thank you!

 

[67cj5]

Thanks for the replies. 67CJ5 that’s exactly what I was hoping to learn. Thank you!

Your most welcome,

Tomorrow I am going to run the same 24hr test only this time I will set the Temp to -10c / 14f maybe -12c /10.4f which is plenty cold enough to keep food frozen for a few days but at the same time allow food in the Dairy section to remain just above freezing point which is the Ideal temp for using a single compartment fridge as a Duel zone fridge, Ok.

hope that helps,

 

[67cj5]

Thanks for the replies. 67CJ5 that’s exactly what I was hoping to learn. Thank you!

Here is a couple of photos taken after 20 hours with the ARB 47L / 50Qt set to -10c, these figures are close enough to 24 hours so if you do the maths you will get pretty accurate 24hr results, -10c / 14f is just about the perfect Setting because it allows you to use the ARB fridge freezers as a true Duel Zone because the temp in the main area actually will drop a couple of degrees lower IE from -10c where it shuts off down to -12/-13c as the Cold Air Sinks, Then as it warms up slightly it will rise to -10c/-9*c and then it repeats the cycle all over again as do "ALL" fridge freezers, With the ARB's you have the option of using them as a fridge OR a Freezer OR by setting it like this you have a combination of both being the best of both worlds,

Setting the ARB to -10c / 14f gives you a good cold temp but also super cools the Dairy area down to as far as -3*c, Which is Ideal for temps needed for a couple of weeks away where long term frozen storage does not apply, It went that low in the dairy area because I only 3rd filled the ARB and put nothing in the dairy area, So I would expect the power usage to be lower with more placed inside.

when set at -10c / 14f, 20.706Ah divided by 20 hrs is equal to 1.0353 Amps per hour.

Next Plan is to set the ARB on it's Maximum Cold Setting and see how the Numbers go regarding the A/h and the W/h.

If you need to know more just call and I will be glad to help.

Hope that helps,

 

[Ducky's Dad]

Perhaps I am oversimplifying this, but the obvious answer is: "It depends." Depends mostly on ambient temps around the fridge and internal temp setting on the fridge. You will burn more amps in Arizona than in British Columbia. More in summer than in winter. Lots of other factors, but those are in the big ones. Example: My Indel B 50 averages about 2.7 amps/hr over 24 hours when set for freezing in 100F+ weather. That is my worst case "typical" scenario, but there are days when it averages over 3 amps continuously. Measurements are approximate, using multimeter to get battery open circuit voltage and then comparing readings to battery manufacturer's Voltage vs SOC tables.

 

[67cj5]

Perhaps I am oversimplifying this, but the obvious answer is: "It depends." Depends mostly on ambient temps around the fridge and internal temp setting on the fridge. You will burn more amps in Arizona than in British Columbia. More in summer than in winter. Lots of other factors, but those are in the big ones. Example: My Indel B 50 averages about 2.7 amps/hr over 24 hours when set for freezing in 100F+ weather. That is my worst case "typical" scenario, but there are days when it averages over 3 amps continuously. Measurements are approximate, using multimeter to get battery open circuit voltage and then comparing readings to battery manufacturer's Voltage vs SOC tables.

Yes I agree, Another thing to remember is that when a fridge is in the back of your Truck, be it a Jeep, Lincoln Navigator Land Rover or Mitsubishi, Being behind the glass no matter if the windows are tinted or not can double even triple the Ambient temperature which also makes fridges work harder, even in 75f being in a vehicle can ramp up the temp to over 90 to 100f,

Mirror window tinting does help a little but the vehicle needs a White roof or be covered in a reflective film, Because the main thing that heats up a vehicle is the Roof NOT the Windows, So if you are summer camping or what ever in a very hot place it would pay to cover the roof of the vehicle with either a Silver Tarp or space blanket Type material to reflect the heat away from the roof and side windows this can drop the inside temp by up to 30*f and in the process reduce the power consumption of the fridge,

 

[luthj]

Off topic, but windows are the primary path for heat entry into a vehicle, especially so in direct sunlight. Most roofs have at least a modicum of insulation, be it headliner material, insulation mat/foam etc. Windows are less than R1 on a good day, and with sun, most of the IR and visible light can pass through. A reflective tint can help (though it can be illegal in some places). Tinting the window dark makes the glass absorb the light energy, turning it into heat. The glass will get much warmer. Since one side of the glass is exposed to the outside air, this reduces heat transferred to the interior, as much of heat heat is convected away by the outside air.

While fridge power consumption will vary a lot with temperature, it is still fairly linear. For a given delta-T (inside fridge to outside fridge), the power used will double for a doubling of the detlta-T. S0 a 40F D-T will use roughly twice the power as a 20F D-T. Once you get near the compressors limits it gets less linear though. In a closed vehicle temps can exceed 60F above ambient in direct sun. So on a 100F day, a close up vehicle can break 160F inside. At that temp most fridge units won't be able to keep the setpoint temp.

I have a 120L fridge with secop/danfoss bd-50 compressor. It has a bit of extra insulation on the sides/top. On a 100F day it will use about 80AH max. That is with a bit of open/close action, freezing a tray of ice cubes, and having the van closed up for 3-4 hours while we are out hiking. This unit does not have the best insulation though. That 80-AH is about a 65% duty cycle. This unit has a freezer, so my fridge section may be fine, but it takes a while to get the freezer down to 10F.

 

[67cj5]

Not True, The Sun when it is at it's hottest is normally above the vehicle and that is when it heats up the vehicle the most Sure some heat comes through the windows but not nearly as much heat compared to the heat that comes off the roof in to the vehicle, It is a well proven fact, The heat that comes through the windows accounts for 15 to 20% of the heat because the Sun is not horizontal to the windows unless at sun rise or sun set, Most of the Dribble about window Tinting are false claims made up by the people who sell the stuff, And Windows are the Primary Source where LIGHT gets in to the Vehicle NOT HEAT. One thing that is in Tinting's favour is that they cut down UV rays and add some form of security making it harder for people to break in via the windows, Having just read an article where someone took a Temp ready before they tinted their windows and then took another reading afterwards and their car was warmer after tinting

I know this to be fact because I have owned many vehicle with tinted windows, Some black tinted some mirror tinted, and both use to get equally hot and one vehcle that was Black with Blacked out windows was the hottest of them all, Very few cars have insulation in their hood lining and there is not enough space between the roof and the hood lining to create a thermal barrier wide enough to have a noticeable impact.

Window Tinting Looks Cool but has very effect and anyone who says different is just spouting sales pitch and false claims put out buy companies who's soul purpose in life is to part people from their money, Period.

 

[luthj]

Yeah, I have done the math for a couple of projects, and the single most effective heat transfer reduction is from insulating the windows, ideally with a reflective panel just inside the window. Some exceptions are vehicles with dark, and very large roofs, or vehicles with no insulation on the roof panel. I don't have the time or energy to disgorge the math and testing here. Do what makes you feel best.

 

[67cj5]

Yeah, I have done the math for a couple of projects, and the single most effective heat transfer reduction is from insulating the windows, ideally with a reflective panel just inside the window. Some exceptions are vehicles with dark, and very large roofs, or vehicles with no insulation on the roof panel. I don't have the time or energy to disgorge the math and testing here. Do what makes you feel best.

Even those guys on Myth Busters tested window tinting and found that fitting a simple sun shade had the same effect and the biggest variation was between 3 and 5*.

Another Guy took temp reading before he tinted his windows and again after he tinted his windows and he found a rise in the temp After he tinted them.

 

[Ducky's Dad]

When my Indel B 50 was new and when my house batteries were new, that fridge would hold -22C when outside ambient touched 128F in mid-afternoon. Fridge had been pre-chilled, some of the stuff went in frozen, fridge was near full, had a pile of clothing (insulation) on top of the fridge, factory window tint, white truck, etc. That was a huge drain on the batteries, but it worked as long as we moved around a couple times per day, usually 70-100 miles per day on a 270amp alternator. Stay parked and the batteries were done in maybe 18 hours. Interior cabin temps would go north of 185F, so delta was about 193F. My ARB 50 can't do that, even though it's new.