[Prev1]

I was curious how much energy a specialty refrigerator uses vs a dorm refrigerator. I looked up the Engel and it says max power consumption of 2.3ah at 12.8v (constant use consumption). When running, the dorm refrigerator seems to be drawing about 130w.

So for the Engel 2.3 x 12.8v = 29 watts per hour?

and the dorm refrigerator:

Dorm 1.2 x 110v = 132 watts

Is this the right comparison? So then using 4.5x the power?

 

[Motor7]

It's tempting because of the price, but in reality, a dorm fridge is really only practical when hooked up to shore power.

 

[Prev1]

It's tempting because of the price, but in reality, a dorm fridge is really only practical when hooked up to shore power.

Do you know if the above is the correct calculation (and not even taking into consideration the inefficiency of the inverter).

 

[GaryBIS]

Hi,
What you need to compare is the amount of energy each fridge uses in a full day. The 130 watts for the dorm fridge is what it uses when its on, but it is only on part of the time, so the 130 watts does you not helpful.
I'm not sure what the 2.3 amp-hrs means - maybe the amount of energy used by an engel in an hour, but that would be 55 amp-hrs a day, which is too high. Maybe its what it would use if its on all the time?
Anyway, neither number is what you want.

This guy measured energy use for a 35 liter Engel and seemed to do a good job it.
He gets about 30 amp-hrs a day depending on temperature.

This guy looks at energy use for several dorm fridges using the the gov numbers on the yellow sticker that comes with the fridge. The average is about 600 watt-hours per day or about 50 amp-hrs per day.
You need to increase this by about 15% to account inverter inefficiency, so about 58 amp-hrs per day.

This is not a perfect way of comparing as different test procedures were used, but it should be in the ball park.

So, roughly...

Engel 30 amp-hrs per day
Dorm fridge 58 amp-hrs per day

Roughly twice as much for the dorm fridge.

There is also the issue that you need to keep your inverter on 24 hours a day, and it uses some energy even when the fridge is cycled off.
It seems like most people that try dorm fridges end up getting 12 volt fridges after a while.

Gary

 

[Prev1]

Gary, thanks for the response. I was trying to eliminate the insulation efficiency and ambient temperature by taking both units running full time. That was the 2.3 for the Enger from their chart and if the dorm refer went 100% of the time, how would they roughly compare.

With that approach, is it not 4.5x the power usage (and as noted above, without the inefficiency of the inverter)?

 

[RamVanGuy]

Keeping inverter on 24/7 is a deal breaker for me.... it costs WAY more energy than just the 15% extra inefficiency for the fridge itself. If I use the inverter as on/off for just the immediate needs - such as coffee maker, then I get 3 days out of my battery bank. If i leave inverter idling I get 1 day.

 

[Prev1]

Keeping inverter on 24/7 is a deal breaker for me.... it costs WAY more energy than just the 15% extra inefficiency for the fridge itself. If I use the inverter as on/off for just the immediate needs - such as coffee maker, then I get 3 days out of my battery bank. If i leave inverter idling I get 1 day.

So I wonder about my facts.

Firstly, I run the refrigerator directly off the battery bank when not running the vehicle, not the inverter, sorry about that, wasn't thinking. But out of curiosity i did check the average consumption when idle and they seem to be small. I saw this discussion:

"If the unit is turned on, the amount of power drawn can vary from around (10V at the minimum of 0.2-amps/1Watts) up to (0.5V at the minimum of 2-amps/1Watts) depending on the unit and design of their standby systems"

I did look at the mini fridge specs and they do seem to be 65w when running. I do know I've seen mine much higher, but maybe that's when the freezer is running, I don't know. I'll have to check that.

Thanks

 

[GaryBIS]

Gary, thanks for the response. I was trying to eliminate the insulation efficiency and ambient temperature by taking both units running full time. That was the 2.3 for the Enger from their chart and if the dorm refer went 100% of the time, how would they roughly compare.

With that approach, is it not 4.5x the power usage (and as noted above, without the inefficiency of the inverter)?

Hi,
I see what you are getting at comparing the power use when cycled on.
To compare them in the same units: dorm fridge is 130 watts when on , and the Engel at 2.3 AH/hr converted to watts would (2.3)(12.5) = 29 watts when on.
This would be the 4.5X difference in efficiency - I very much doubt there could be anywhere near this much difference in efficiency between two compressor fridges - see next paragraph.

I'm not sure that helps you in that they may not be producing an equal amount of cooling when cycled on. That is, the Engel may run 40% of the time to produce the same amount of cooling as the dorm fridge needs to run 60% of the time to produce - I just pulled these numbers out of the air, but you get the idea. The two fridges would have to be producing the same number of BTUs cooling to compare their efficiency by comparing their power use when cycled on.

Gary

 

[RV8R]

Hi @Prev1

I have the same choice to make for my Cabin. Although it is a different install than a van, the parameters I have thought about are;

1. Total Energy Consumption of the 2 different systems
2. Increased interior heat produced by the 2 systems
3. Dorm Fridge vs 12vdc RV Fridge - operational differences - “Frost Free” fridges use a lot of juice in comparison ,,, brought to my attention a year ago by @HarryN in our posts ,,, thanks Harry 👍
4. Inverter efficiency & even more important is “standby” energy used

Depending upon the season, heat generated by electrical equipment & appliances can be counter productive (especially in a small volume space as a van).

12vdc fridges are expensive (not frost free - or most are not) & very efficient for 12vdc supplied energy.

Other than the parameters above, do you have other parameter concerns?

Also, there are things that you can do to increase fridge efficiencies ,,, in my van I added 1” of polyiso foil-face around the 4 sides & top of my Truck Fridge “TF130” (not on the bottom).

 

[Bromaster5]

I was curious how much energy a specialty refrigerator uses vs a dorm refrigerator. I looked up the Engel and it says max power consumption of 2.3ah at 12.8v (constant use consumption). When running, the dorm refrigerator seems to be drawing about 130w.

So for the Engel 2.3 x 12.8v = 29 watts per hour?

and the dorm refrigerator:

Dorm 1.2 x 110v = 132 watts

Is this the right comparison? So then using 4.5x the power?

My 21 cubic foot fridge in my kitchen that's a decade old consumes 120 watts fyi...

 

[HarryN]

Total cost of implementation ends up coming out surprisingly similar.

Just as a first order approximation estimate:

1) 12 / 24 volt type refrigerator

• Wanting to be pretty sure that it will keep running
• Nominal 2 x 100 amp-hr, good quality batteries (minimum )
• ~ 400 watts of solar,
• Sometimes needing some grid or alternator charging

2) Decent quality 120 vac refrigerator

• Wanting to be pretty sure that it will keep running
• Nominal 4 x 100 amp-hr batteries (minimum)
• ~ 800 watts of solar

So it is more costly, but not that much.

If you want to really run a 2 kW inverter without issues, it takes this size battery pack anyway.

Now you have 120 vac available for other uses all of the time as well.

So it is mostly a matter of where you want to put approximately the same money.

As @RV8R mentioned, some of the power goes to the built in defrost heaters, but that is also a benefit.

 

[Lolaeliz]

So I wonder about my facts.

Firstly, I run the refrigerator directly off the battery bank when not running the vehicle, not the inverter, sorry about that, wasn't thinking. But out of curiosity i did check the average consumption when idle and they seem to be small. I saw this discussion:

"If the unit is turned on, the amount of power drawn can vary from around (10V at the minimum of 0.2-amps/1Watts) up to (0.5V at the minimum of 2-amps/1Watts) depending on the unit and design of their standby systems"

I did look at the mini fridge specs and they do seem to be 65w when running. I do know I've seen mine much higher, but maybe that's when the freezer is running, I don't know. I'll have to check that.

Thanks

A Dorm fridge (meaning a small 120v AC fridge in the $100-200 price range) needs the inverter on 24/7. Only 12v runs directly off the batteries. The inverter converts the 12v power to ac 120v. My inverter/charger alone is a power hog, so running it 24/7 would knock any dome fridge out of consideration. Maybe check out truck fridges. Those are 12v but have a lower price point. I think a few people here have them and like them. As much as I consider my iceco chest fridge/freezer to be a power hog, it was cheap, and it's certainly better than the dorm fridge. I've become a convert from front opening to chest fridges. They just hold more food.

As far as your numbers being accurate... I find that with fridges there are too many variables to give the numbers too much importance, and 12v fridges are expensive. So maybe choosing the best 12v fridge you can find at a price point you're happy with is the way to go.

 

[Prev1]

This has been really interesting, thank you all for providing great feedback. There's a reason most people do the whole process in similar ways, because it has been time tested and works.... anyway...

Harry N, it seems that depending on where I travel, I can fully run a 120v refer for a portion of the day and sometimes charge the batteries also just using a 200w solar panel putting out much less (like 75w). The land power or running time I need varies widely between CT and FL. So really wondering how much longer it would go in a particular situation before I needed land power. Your cost is based on purchasing stuff to design it from scratch. If only that was the way I went from day one!

GaryBis, you raise yet another critical factor in the analysis (and this is the opposite of what you said, but same issue) does the 12v unit put out less cooling when running, so it runs longer to cool same amount (maybe to increase its efficiency). Basically, is it throttled down. If so, maybe the dorm runs 30 minutes per hour and the 12v runs for 43 minutes to maintain the same temp?

Ideally, I would run both in the van at the same time and see what happened.

Lolaeliz, the refer runs on 110v from a 560wh LI battery (i have two batteries this size installed). So yes, there must be an inverter in those units.

The key question is an approximation of whether the refer is using one, two, three or more times what a 12v refer would use. So, if they were both in the same environment, how much difference is there in power usage.

I will call a manufacturer and see if I can connect with someone who knows.

I will update once/if I get someone on the phone.

Thanks!

 

[phil]

-an inexpensive load sensing inverter may be out there
-a diy temperature controlled inverter is doable

either one will reduce inverter idle wattage

but are the added components and monkeying time worth it

 

[GaryBIS]

T

GaryBis, you raise yet another critical factor in the analysis (and this is the opposite of what you said, but same issue) does the 12v unit put out less cooling when running, so it runs longer to cool same amount (maybe to increase its efficiency). Basically, is it throttled down. If so, maybe the dorm runs 30 minutes per hour and the 12v runs for 43 minutes to maintain the same temp?

Thanks!

No no no - it makes no difference if its a 12 volt DC motor or a 120 VAC motor. Either can be designed for any horsepower output. There is no inherient reason that a 12 volt motor compressor would run longer than a 120 VAC motor.

Gary

 

[keeponvaning]

For many, many years I ran a dorm fridge (in a sprinter and my ‘14 Promaster) with nothing but 2 - 6v GC’s batteries and a 2000w inverter. They never failed me although it was always a concern. I ultimately upgraded to a 12v TruckFridge 130, however, and I am very happy with it. It runs on my 2 flooded 6v GC batteries which are charged both by the alternator and/or my 340 w of solar. Now, I only turn the inverter on for a few minutes each day to make coffe, use the microwave or cook on the induction cooktop. I’ve NEVER had a power problem with this setup and always have cold beer & hot coffee!😏

 

[Motor7]

Something else to consider. Yes, someone on here will tell us that when G-ma went to college she bought a Dorm Fridge back when elevators had "Operators" running them, and dang if the thing is not still running 87 year later. The dorm refers these days are junk. In my shop, I have gone through three of them in 10 years. The last one had a nice sized Eastern Diamondback in the freezer that was going to get made into a belt. Refer failed, didn't notice for a month...in August.....can you say .....liquified snake? No more dorm fridges for us....

On the other hand, if one does fail, grab a cart and zip into WallyWorld for another one.......

 

[wbullivant]

I was curious how much energy a specialty refrigerator uses vs a dorm refrigerator. I looked up the Engel and it says max power consumption of 2.3ah at 12.8v (constant use consumption). When running, the dorm refrigerator seems to be drawing about 130w.

So for the Engel 2.3 x 12.8v = 29 watts per hour?

and the dorm refrigerator:

Dorm 1.2 x 110v = 132 watts

Is this the right comparison? So then using 4.5x the power?

I bought my 4.5 cf Frigidaire S&D 'dorm fridge' for ~$130 in 2015 and it has performed well since then. I use it with a 2kw Samlex PSW inverter that runs 24/7. I haven't run measurements on power consumption but I can tell you that overnight my battery monitor says it along with my two Maxxair fans consume no more than 5% of my four GCB pack capacity. I have added small fans inside and out of the frig to improve air circulation and the cooling is very dependable as long as I leave enough space inside for some air movement. Perhaps a more expensive 12v model would be superior but my current setup is 'good enough'.

I just got back from two weeks of off grid camping at Fort Pickens CG in Pensacola, FL and my 8YO battery pack stayed above 80% the entire time in generally sunny weather with no tree cover.

 

[Paul Niedermeyer]

I've used an Energy Star Magic Chef 3.5 cf dorm fridge for 5 years now, and it's worked very well. I did add extra rigid insulation on the back, top, and bottom (not sides, as that's where it throws off its heat. I have 2x6 Volt FLAs and a 2000 W inverter. In the morning, my battery SOC is usually still over 90%, sometimes mid 80s. I have a solar panel, so it charges up quickly once the sun comes out.

I did run a few tests with a Kill-a-Watt meter in mild early summer weather (around 75 degrees daytime) I measured three multi-day stretches with daily consumption of 350, 335, and 278 watt hours. These are very low numbers, corresponding to about a 110 kWh/year, or half its Energy Star label rated consumption. Undoubtedly that’s in part to the extra insulation, but the weather/heat load was probably lower, due to the cooler nights. I am convinced that it is quite efficient, and not that far from the 12 V units.

I've driven our van on quite a lot of rough and rocky roads, and the unit is still running fine. And my 6V batteries are still totally healthy after 5 years. So I'm happy with my choice, and have no issues.

Having said that, I'll most likely replace it with a 12 v unit if/when it dies. There are many more options now available than back then.

 

[HarryN]

I've used an Energy Star Magic Chef 3.5 cf dorm fridge for 5 years now, and it's worked very well. I did add extra rigid insulation on the back, top, and bottom (not sides, as that's where it throws off its heat. I have 2x6 Volt FLAs and a 2000 W inverter. In the morning, my battery SOC is usually still over 90%, sometimes mid 80s. I have a solar panel, so it charges up quickly once the sun comes out.

I did run a few tests with a Kill-a-Watt meter in mild early summer weather (around 75 degrees daytime) I measured three multi-day stretches with daily consumption of 350, 335, and 278 watt hours. These are very low numbers, corresponding to about a 110 kWh/year, or half its Energy Star label rated consumption. Undoubtedly that’s in part to the extra insulation, but the weather/heat load was probably lower, due to the cooler nights. I am convinced that it is quite efficient, and not that far from the 12 V units.

I've driven our van on quite a lot of rough and rocky roads, and the unit is still running fine. And my 6V batteries are still totally healthy after 5 years. So I'm happy with my choice, and have no issues.

Having said that, I'll most likely replace it with a 12 v unit if/when it dies. There are many more options now available than back then.

That is actually very good efficiency.

With numbers like that, it is tempting to just use a good full size refrigerator.

I have wondered how much of the Energy Star rating is from actual refrigeration vs defrost cycles.

So you are using just 250 amp -hrs @ 12 volts of battery pack and 300 ish watts?

Is this in an area with fairly clear sky?