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Experimental results powering a freezer with batteries

This is a discussion on Experimental results powering a freezer with batteries within the Alternative Energy (Wind, Solar, Hydro etc) forums, part of the Off-Grid Lifestyle category; Originally Posted by Redneck I addressed this issue of having a freezer during extended power outage, after the generator dies, by having an ARB 50 ...

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Thread: Experimental results powering a freezer with batteries

  1. #11
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    Quote Originally Posted by Redneck View Post
    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...
    sideKahr likes this.
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  2. #12
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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-Elec...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-3...words=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.
    Last edited by John Galt; 04-17-2017 at 07:28 PM.
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  3. #13
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    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-...tt+solar+panel @sideKahr
    Last edited by John Galt; 04-17-2017 at 07:28 PM.
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  5. #14
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    Quote Originally Posted by John Galt View Post
    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-...tt+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.
    Last edited by sideKahr; 04-17-2017 at 08:46 PM.
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  6. #15
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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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  7. #16
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    Quote Originally Posted by azrancher View Post
    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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  8. #17
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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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  9. #18
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    Quote Originally Posted by sideKahr View Post
    . 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.
    sideKahr likes this.
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  10. #19
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    Quote Originally Posted by John Galt View Post
    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.
    John Galt likes this.
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  11. #20
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    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?
    Last edited by sideKahr; 04-18-2017 at 03:22 PM.
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