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Discussion Starter · #1 ·
I've seen the question repeatedly on the internet: "Can you run a freezer on batteries if the grid power goes down for a few days?" The articles I've read predict 17 to 24 hours of run time for a 100 amp hour battery. They recommend using a gasoline generator. I decided to try a real world experiment using battery power.

Well, my results were measured in DAYS, not hours!

My chest freezer is nothing special, it's a small 4.8 cubic foot Kenmore from Sears. The door gasket leaks a little, but it keeps food at 0 degrees F - an adequate machine. My 2 batteries are Duracell Marines from Batteries Plus, 79 amp hour each wired in parallel, and powering a Xantrex 1000 watt pure sine inverter. It's a plain vanilla battery backup system if there ever was one, right?

I ran the freezer for 130 hours, more than 5 days, on that setup. The batteries showed an open circuit voltage of 12.0 at the end of the test, which is a healthy 50% state of charge for an AGM battery. The dozen 1-liter water bottles inside were still frozen solid. In a real emergency, I'd have no problem running the batteries down to exhaustion, and many more days of food preservation would be possible.

It's the METHOD that yields the unexpected results. By powering the inverter only when the inside temperature of the freezer rose to 30 degrees F, and then cooling it back down to zero, battery power was conserved in a big way. The inverter needed to run for only 1 hour every 8 to maintain below freezing temps. In between power-ups I covered the unit with some doormats and an old down jacket for extra insulation.

Next blackout, when everyone is opening the canned spam, I'll be inviting the neighbors over for steaks and burgers and some very cold brewski's. Just call me Mayor SideKahr.
 

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I have scoured the internet for answers to the 40 deg F, and 0 deg F temperatures for refrigerators, and freezers, and except that the FDA "says so", scientific proof is not readily available, except that some foods do not freeze at 32 deg F, like salt water at 28.4. OK I did not scour the internet, I spent 4 minutes, and 37 seconds looking up this answer... I think if SHTF or a Hurricane, or a power outage, that if you had a thermostat controlled freezer that was battery powered you would want the temperature to fluctuate between 22 and 28 degrees F, why because I think the 0 degrees/40 degrees is the school book answer from the FDA to cover food brought home from the store and needed to be quickly frozen, hence 0 degrees was a good answer, but once it's frozen you just want to keep it from thawing, refreezing, vacuum packing will reduce the frost from the food moisture out gassing. @sideKahr what did you use for a thermostat control?

Rancher
 

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I also have a small, inexpensive chest freezer set up to run off solar. I cut, fit, and glued 1 inch thick styrofoam sheet insulation on all 4 sides. I also fashioned an easily removable lid to cover the top and gasket area. I have no concrete data to share but I know I increased the insulation value of the freezer. Cheap too.
 

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Discussion Starter · #4 ·
...@sideKahr what did you use for a thermostat control?Rancher
I did it manually. The first few cycles I'd peek in every hour to read the temperature, and after a while I could predict when I needed to turn on the system.

I didn't want to overcomplicate the report, but when I said I cycled the temp from 0 to 30, that isn't the whole story. Those are temps up near the lid. At the bottom of the freezer, the temp never exceeded 24 degrees F, and cycled from -5 to 24.
 

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I addressed this issue of having a freezer during extended power outage, after the generator dies, by having an ARB 50 qt refrigerator/freezer. It only pulls 1.35 amps/hour so my solar generator can run it, as my latest has a 100 amp hour battery. Not a full blown chest freezer, but works with what I have.

 

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Discussion Starter · #6 ·
I also have a small, inexpensive chest freezer set up to run off solar. I cut, fit, and glued 1 inch thick styrofoam sheet insulation on all 4 sides. I also fashioned an easily removable lid to cover the top and gasket area. I have no concrete data to share but I know I increased the insulation value of the freezer. Cheap too.
There's a guy on YouTube, he's actually pretty smart, who took your method to extremes by insulating the motor/compressor compartment from the interior with foam:

 

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Discussion Starter · #7 ·
I addressed this issue of having a freezer during extended power outage, after the generator dies, by having an ARB 50 qt refrigerator/freezer. It only pulls 1.35 amps/hour so my solar generator can run it, as my latest has a 100 amp hour battery. Not a full blown chest freezer, but works with what I have.

That's a pretty cool unit, Redneck (pun intended)! Steven Harris, who's been on Jack Spirko's Survival Podcast many times, recommends foregoing the chest freezers entirely and just using a low amp tabletop icemaker and coolers.

I guess that's okay for beer and butter, but I'm looking to keep my freezer working to save some high value meats during a blackout.
 

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That's a pretty cool unit, Redneck (pun intended)! Steven Harris, who's been on Jack Spirko's Survival Podcast many times, recommends foregoing the chest freezers entirely and just using a low amp tabletop icemaker and coolers.

I guess that's okay for beer and butter, but I'm looking to keep my freezer working to save some high value meats during a blackout.
My whole house natural gas generator & my smaller portable gas generators should help me for the short term, but I prep for the long term. But even if I needed this for short term, my thought was using this to make 50 (probably less) quarts of ice at a batch could keep keep meat in the freezer from going bad so quick & buy time to either use that meat or to can it. For extended SHTF, my goal is mainly to extend the storage time of fresh meats, to give us time to process them for long term storage. I have some really nice, high end, very efficient ice chests to work hand in hand with this freezer. That is how I plan on using this unit. But love what you have done.
 

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.

- Did you just happen to have a pure sine inverter, or did you get it just for the purpose? I haven't noticed any problems running freezers from a modified sine inverter.

.
 

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Discussion Starter · #10 · (Edited)
.

- Did you just happen to have a pure sine inverter, or did you get it just for the purpose? I haven't noticed any problems running freezers from a modified sine inverter.

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I'm planning on installing a photovoltaic powered system. I bought the pure sine wave inverter because I don't know how far I'm going to take this project, and I didn't want to have buyers remorse with a modified SW unit. That's also why I overengineered the system with 2/0 and 1/0 AWG cables; I might need more batteries.

P.S. FYI, a modified sine inverter will NOT charge my wife's Tracfone. It just continually restarts itself.
 

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I addressed this issue of having a freezer during extended power outage, after the generator dies, by having an ARB 50 qt refrigerator/freezer. It only pulls 1.35 amps/hour so my solar generator can run it, as my latest has a 100 amp hour battery. Not a full blown chest freezer, but works with what I have.

I have 35 year old version of this. Run on 12 VDC or 120 VAC. On a fishing trip in Wisconsin during the mid
summer I got 4 plus days running it to freeze my catch. It was running about zero and was in the shade of
my trailer. I was using a 27 series marine battery (don't remember much else). I still have it and it runs
very nicely. Using it for refrigeration, I would guess I might get 7-8 days on a similar battery. Would be
great for storing meds, etc. It holds about 46 -12 ounce beer cans and I only use it for parties, right now...
 

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My thoughts in the previous posts
1. I'd strongly recommend getting a Kill A Watt meter for accurate instant and over time total power measurements $19.75 https://www.amazon.com/P3-P4400-Ele...qid=1492477160&sr=8-5&keywords=watts+up+meter
It can be used for all sorts of 120v stuff around the house.

2. Because of the start up surge most compressors require you may see a very slight improvement in power efficiency if you cycle from 30 degrees down to 0 degrees instead of keeping the freezer between 0 and 5 degrees. While uncommon in the US, inverter type compressors for refrigerators and freezers are more efficient (when you don't muck about with the temperature every few hours), and generally cost more. If instead you muck around with the temp setting every few hours an inverter type compressor may use more electricity than if you had just set a temp and left it alone.

3. For refrigerated items USDA testing shows that bacteria growth begins to really speed up in temperatures over 41 degrees. That's why most refrigerators can't be set warmer than 40 degrees.

4. If you do want to set a refrigerator (or freezer) outside it's normal range there are many devices that do this. I use an InkBird ($35) to convert an old chest freezer into a temperature controlled box for aging beer. https://www.amazon.com/Inkbird-Itc-...qid=1492477912&sr=8-1-spell&keywords=inkbiird

5. Keep in mind that if you intend to run a regular motor (like a fridge has) off a modified sine wave inverter the motor will burn out within a few months, a year at most. Get a pure sine wave inverter (like sideKahr did) and get one large enough to handle the motor's start up surge. The start up surge can be 2 to 3 times the motors normal draw under load.
 

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Discussion Starter · #14 · (Edited)
You may find that a 100 watt solar panel with a cheap PWM controller can keep that fridge running for years. If you live in a cloudy area you may need 2 panels.
https://www.amazon.com/Renogy-Watts...92478614&sr=8-3&keywords=100+watt+solar+panel @sideKahr
Yep, that's my plan. I'm still researching whose equipment I want to obtain.

I also recommend the Kill-A-Watt meter. Very useful item to have, and it tests to within 1% accuracy vs laboratory instrumentation.
 

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On my way to a EE degree, I attended a college (party college) for my 3rd year, I was forced to take Thermodynamics, and other weird engineering courses, so I would design the freezer to not go as low as zero degree F, like I said in the second post, 20 is probably good enough, it's the delta T that uses energy, i.e. the more the difference between the inside of the freezer and the outside temperature is what takes energy to achieve, less is better, re-freezing to zero each cycle looses more energy than just re-freezing to 20 degrees F. Make Sense? @sideKahr try it and report back!

Rancher
 

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Discussion Starter · #16 ·
On my way to a EE degree, I attended a college (party college) for my 3rd year, I was forced to take Thermodynamics, and other weird engineering courses, so I would design the freezer to not go as low as zero degree F, like I said in the second post, 20 is probably good enough, it's the delta T that uses energy, i.e. the more the difference between the inside of the freezer and the outside temperature is what takes energy to achieve, less is better, re-freezing to zero each cycle looses more energy than just re-freezing to 20 degrees F. Make Sense? @sideKahr try it and report back!

Rancher
Okay, I'll try it. I purchased a new digital multimeter with a remote temperature sensor, which should make the whole process easier.

My advance guess is it will actually take more energy to cycle between 20 and 30 degrees F.

Here's my reasoning: When the cycle starts at 0, it has 30 degrees to rise before the inverter must power up. I know that takes about 8 hours. But when the cycle starts at 20, it will reach 30 much quicker, probably in about 2-3 hours, requiring the freezer to start more often in any 24 hour period. True, it has to run for a shorter period to drop from 30 to only 20. But watching the Kill-A-Watt meter it's obvious that much more power is used to start the compressor than during running, > 120 watts vs. 80 or so. I would think minimizing the number of startups would be desirable.

We shall see.
 

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Yes there is a breakeven point between the energy used for more startups vs losses due to a bigger delta T, I pulled that 20 degrees outta my hat, or somewhere lower...

Rancher
 

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. But watching the Kill-A-Watt meter it's obvious that much more power is used to start the compressor than during running, > 120 watts vs. 80 or so. I would think minimizing the number of startups would be desirable..
The initial motor start up surge is probably much higher than the 120 watts your seeing. It happens pretty quick, too quick for most meters to pick up unless the meter has a highest level memory function you and review it later. But using the DR watts meter for say 24 hrs with both the 20-30 degree range and the 0-30 degree range with similar outdoor temperatures should tell you which is more efficient.

As was mentioned earlier in this thread some things (especially if they have some salt in them) need to be colder to freeze so maybe make the upper temperature 28 degrees.
 

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Discussion Starter · #19 ·
The initial motor start up surge is probably much higher than the 120 watts your seeing..As was mentioned earlier in this thread some things (especially if they have some salt in them) need to be colder to freeze so maybe make the upper temperature 28 degrees.
I'm sure it is, it's a slow reacting meter with no memory. I thought I saw it briefly hit 145 watts once.

About the salted food resistance to freezing, thanks. I'll modify the cycle to 18-28 degrees F.

I won't be able to start the second test right away because, believe it or not, the internal temperature of the freezer is STILL below 30 degrees. The last electricity input was more than 12 hours ago. The temperature probably won't rise above the freezing point until all the frozen water bottles have melted; it's taking longer than I thought it would.
 

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Discussion Starter · #20 · (Edited)
I really don't understand how batteries work. I kept track of how much energy was used by the freezer during the test with the Kill-A-Watt meter; it was 970 watt hours. That's fairly close to the theoretical energy available at 50% depth of discharge (800 watt hours for these batteries) using 85% inverter efficiency.

The batteries just finished charging, estimated by when the smart charger switched to float voltage. The charge required 1740 watt hours. Thats a big difference. What's causing that? I've read that batteries have an internal resistance, but I don't understand why. Could that be the reason they need double the energy to get back to where they were?
 
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