Solar Powered Fridge

[jwh92020]

Tony - That's more polite than what I said!

[flboy]

Keep in mind the compressor on a Dorm fridge does not run 24hrs/day. The 639 ah seems excessive for what you described.. something is awry with the calculations? The battery bank only has to carry you during darkness and your panels keep up with usage during day and excess stored in batteries. I have 430aH (215ah useable) and 500w solar and it is way more than I need running much the same if not more.

The fridge may run 25% of the time or less on coldest setting depending on ambient temps and in and out usage. I have a 4.3 CU ft. Magic Chef and it uses less than about 60W to include inverter losses when running. A 12vdc compressor will save the power conversion losses, so a little more efficient. Not sure it is enough of a gain to pay the premium for (dorm fridge cost $125 vs $600+ for DC fridge). It would be cheaper just to add another 100w panel for $100 and be way ahead of the power game. On average it would take the equivalent of about 360W for an hour (30 amp hrs.) to run the dorm fridge all day as worse case. A 100w panel in good sunlight for 6 to 8 hours would sustain itself with margin. Add more panels for the other stuff and to make up for poor conditions. Probably need to do that anyhow and you would likely have other uses for the inverter as well. I know I do.

Just some data to help make decisions with.

I have been using a 4.3 cu ft. Majic Chef for 3 years now and love it, except it freezes things below the freezer box if you have on coldest setting and do not watch it. I used a 3.2 cu ft. dorm fridge for 5 years in old CTC and it was sold with the CTC. I had a 200w system with 125aH of batteries and never came close to running low on batteries with good sunlight running the fridge and basic fan and lighting. Had a gen to charge otherwise. Best to have one of those anyhow for backup.



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[jwh92020]

Don - Thanks for the input. 639 amp hrs seems awfully high to me as well. I got those 3s from a calculator in a Facebook Solar Rv group. The frig is 110v and draws 0.8 amps/44 watts when running. I haven't plugged on in and let it run for any length of time. I suppose I could plug it into a kill a watt meter and let it go for a few days and see what actual run numbers are. In talking to Dish Network, the Wally receiver for the portable dishes runs 40 watts my 32" led tv (Insignia brand) says 60 watts. That's 100 watts for 6 hrs +/- nite I'm looking for a lower watt draw tv. I found a 24"monitor that uses a 12v power supply and draws 22 watts. Since I'll be using the trailer as a mobile motel room, tv is kind of important. Other than the tv & fridge, I'll have 2 12v led lights at 6 watts each (full power) 72 watts 6 hrs/nite, a water pump that pulls 3 watts when running (15, maybe 20 minutes max per day) and my laptop (90 watts - 1 hr to charge.) Maybe I entered something wrong in the calculator.

[John61CT]

An efficient 12V compressor fridge will rarely go over 40Ah per day.

Maybe double that in freezer mode, and/or tropical ambient temps.

A very tight & thickly insulated box will allow that budget to cover a pretty large volume of food storage, even operating a freezer + spillover design for the fridge side.

Holding plate designs allow for making use of "free excess" energy from alternator / running genny, and solar when after the bank is getting Full.

But the up-front investment gets higher to get these marine-quality features.

A great Engel or ARB portable fridge is pretty cheap at under a grand, occasional sales, sometimes come up on eBay or CL.

[Solarseniors]

Unique UGP-108L1 is an excellent choice. Look at Ben's Discount Supply for info.Once the unit cools,it's using 1.5_1.7 amps to maintain at 12v.love mine.

[bdosborn]

Can you post the values the calculator used for your loads? While you have a bunch of devices, the calculator seems way high. Take out the laptop charging and those are the devices I typically use, more or less, in a night. I use ~40 a-hrs a night according to my Trimetric meter. Two golf cart batteries does me just fine. It's probably the fridge that is the problem. Remember that 0.8 amps at 120V is 90-100 amps at the inverter input. That's why I have a 12V DC fridge, they are way more efficient.

Bruce

[bdosborn]

I have a 4.3 CU ft. Magic Chef and it uses less than about 60W to include inverter losses when running. A 12vdc compressor will save the power conversion losses, so a little more efficient. Not sure it is enough of a gain to pay the premium for (dorm fridge cost $125 vs $600+ for DC fridge).

I measured the electrical usage of my CF-40 and it's more efficient than you might guess, using about 0.5 amp-hrs:



Note that the duty cycle is 12% and it draws 4 amps (48 watts). My TV/Kodi box set up uses way more energy at 3.3 amp-hrs.

Bruce

P.S. Outside and interior temperatures make a big difference in energy use. I think it was in the 75-80F range in my garage. It goes up a lot (probably doubles) if its 90-100F out. But that's usually during the day when the PV panels are in production.

[jwh92020]

Bruce - The calculator is in the Files section of the "RV Solar For Dummies & DIY group on Facebook. They are reaaly protective of their stuff. I'll see if they're ok with me posting the link to my calculator results.

[flboy]

I have a 4.3 CU ft. Magic Chef and it uses less than about 60W to include inverter losses when running. A 12vdc compressor will save the power conversion losses, so a little more efficient. Not sure it is enough of a gain to pay the premium for (dorm fridge cost $125 vs $600+ for DC fridge).

I measured the electrical usage of my CF-40 and it's more efficient than you might guess, using about 0.5 amp-hrs:



Note that the duty cycle is 12% and it draws 4 amps (48 watts). My TV/Kodi box set up uses way more energy at 3.3 amp-hrs.

Bruce

P.S. Outside and interior temperatures make a big difference in energy use. I think it was in the 75-80F range in my garage. It goes up a lot (probably doubles) if its 90-100F out. But that's usually during the day when the PV panels are in production.

Is that chart showing about 11.1 aH total over 24 hrs? Assuming I am reading it correctly and the CF40 is about 1.3 CU Ft (37 liters), it appears to work out the same or close enough to the same given the size/capacity allowance given the 4.3 cu ft. @ ~ 30-40 aH over 24 hours? Those little dorm fridges are very efficient.... not ruggedized however. Need to be mounted securely indoors and out of the weather.

BTW.. nice data acquisition and charting. What equipment are you using?

[tony.latham]

You get some good advice on this forum, but when it comes to electricity --and Bruce aka bdosborn is chiming in-- it's time to listen and pick his brain.



Tony

[bdosborn]

Is that chart showing about 11.1 aH total over 24 hrs? Assuming I am reading it correctly and the CF40 is about 1.3 CU Ft (37 liters), it appears to work out the same or close enough to the same given the size/capacity allowance given the 4.3 cu ft. @ ~ 30-40 aH over 24 hours? Those little dorm fridges are very efficient.... not ruggedized however. Need to be mounted securely indoors and out of the weather.

BTW.. nice data acquisition and charting. What equipment are you using?

Yup, your absolutely right about the size versus energy use. I have an upright 12V fridge with the same Danfoss compressor as the Dometic CF-40. It's about twice as big, runs twice as often and it uses about twice as much energy.

For the data logging; I have a Sunsaver MPPT Solar controller that will interface to a laptop. It logs the watts, volts, etc. it sees on the accessory line and time stamps it. I just dumped the log into a spreadsheet and graphed it.

Bruce

[bdosborn]

You get some good advice on this forum, but when it comes to electricity --and Bruce aka bdosborn is chiming in-- it's time to listen and pick his brain.



Tony

Thanks Dude!

[bdosborn]

I made a quick spreadsheet to total up your usage and show a battery size. I tweaked the amp-hrs for your devices based what I've seen on my Trimetric meter. I have a 32" insignia TV and it only draws about an amp-hr because I have it connected directly to 12V instead of using its power brick. I've used a Dish Receiver and it doesn't use as much as the nameplate rating; that's the maximum it can draw, not the average. I added a design factor of 20% because I ALWAYS use more power than I think I will. A 3 day battery capacity is typical. The dish receiver it the big draw non-essential load, I'd look at reducing that. Maybe OTA TV instead? Read a book?

I added a couple more things I thought you'd probably use. These results are a little skewed because the fridge will be running in the day, when your PV will be in production. The 3 day reserve assumes that you'll have no PV at all for 3 days (which has happened to me).

Two batteries is probably the practical limit for a teardrop as they weigh 67# each. You can add more later if you decide you need more capacity. Personally, I have a Yamaha 1000W generator as a backup rather than more batteries. Weighs a little less than a single battery and works in the dark.

The most important item to have when living off grid, IMHO, is a battery meter that tracks amp-hrs (Trimetric and Victron are the big names). You need to know when to turn the TV off because your batteries are low or you'll over discharge them and ruin them.



Pm me and I can send the Excel spreadsheet (or did they disable that?)

Bruce

[sagebrush]

This worked 4 years with our Scamp and starting 2nd year in CT conversion. 65 quart Truck Fridge, led lights, Suburban furnace, 100 watt solar panel mounted flat on roof, one group 29 deep cycle battery.

Relax, it's a camper ,not the space shuttle.

[jwh92020]

Bruce - Sent you a PM, we'll see if it goes through. The problem with living in OKC is that stuff like used 12v fridges & such don't come up for sale very often, and when they do, folks here want new retail $ for them.

Sagebrush - When it comes to me & solar, the Space Shuttle would be easier to build.