Right or Wrong

PluckaPlucka Registered Users Posts: 125 ✭✭
Almost every night I turn my inverter off .This turns off my fridge and freezer. In the morning I turn it back on which immediately powers up the fridge and freeze whose power switches were left on. Is this a bad practice? 
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  • BB.BB. Super Moderators, Administrators Posts: 31,758 admin
    It depends... Probably the greatest "hit" is possibly your food... Monitor the temperatures in the AM and see if they have risen enough to be "unsafe" or at least, shorten the storage life of your food.

    Back in 2006, I found a US Gov study (circa 1945) on the best freezer temperature for long term food storage... At that time, they decided that 0F or cooler was best... And even 5F showed food losing a bit of its quality. So, if you are looking for long term storage of frozen food, you don't want the temperature to rise much above 0F.

    On another issue--I have always associated "temperature cycling" with the acceleration of "freezer burn". The food warms up a bit (still well below freezing), freezer compressor turns on an dramatically lowers the air temperature the the freezer--Causing "sublimation" (water ice turning to water gas) of ice from the food to the inside surface of the freezer bag/container... If the overnight temperature transition is not very much--I guess that freezer burn would be less of an issue.

    There is probably not much energy saved in turning off the compressors overnight... Although, if you only run the compressors when the "sun is up"--The batteries are certainly cycling less.

    There is also the question of how your frost freeze fridge/freezer (?) respond to "power outages". The simple/cheap units I typically buy have a mechanical timer that probably advances the defrost timer while the compressor is running--Turn off the AC power, no running compressor, power starts up and defrost cycle will start when compressor cycle timer kicks off (ignoring the question of cutting power during defrost cycle--Evaporator heating element needs to heat hot/long enough to defrost light icing--Does lack of compressor cycle after defrost "heat" the fridge/freezer enough to cause food storage issues?).

    The more expensive fridge/freezers may use an electronic defrost timer--And somebody here reported that their fridge (?) started a defrost cycle as soon as the power was restored. Probably a bit of a waste of power (more defrost cycles than necessary?).

    And there is the question of inverter "tare losses" (idle current just from the inverter being "on")... For larger inverters, it is probably in the 10-40 Watt range (some are higher) if you leave them running over night.

    So how much power is that costing you? Say fridge and freezers use about 1,500 Watt*Hours per day (average SWAG for relatively efficient units). Say you turn them off for 10 hours a night:
    • 20 Watt inverter Tare (SWAG) * 10 hours = 200 WH per day
    • 1,500 WH per cooler * 2 coolers = 3,000 WH per day
    • 200 WH savings / 3,000 WH per day = 0.07 = 7% energy savings (again, just a guesstimate)
    Of course, you are cycling the battery bank much less overnight. Need more information on battery bank AH capacity, voltage, and type (you are using LeFePO4 batteries?).

    Overall, you are probably not saving much energy (inverter off ~200 WH per day)--And assuming you solar array probably harvests around 4,000 to 6,000+ WH per day (rest of house loads, location, over sized array for winter/less genst usage, etc.)--200 WH is pretty much roundoff error in your system usage.

    Anyway, my first set of reasonings and guesses.

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mcgivormcgivor Solar Expert Posts: 3,842 ✭✭✭✭✭✭
    From experience I would have to say it's a bad practice, because it impossible to predict the temperature of the product you are attempting to preserve by keeping it cold in the first place. Dairy products seem to suffer rapidly from variations in temperature, milk develops a sour smell and cheese develops mould, probably due to the bacterial culture used to create it. 

    My attempts to use a freezer as a refrigerator in my infancy of offgrid living by shutting down overnight resulted in spoiled product, I bit the bullet and sized the battery to support 24 hour operation with no regrets. We all experiment often to find out from others experience, or our own, that what at first seems like a reasonable idea, would be proven otherwise.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • PluckaPlucka Registered Users Posts: 125 ✭✭
    Thanks for the replies but my enquiry was aimed at the inverter. Would often starting the inverter under load damage or shorten the life of the inverter. The main reason I turn it off over night in my van is because in the past I've had several cheap 2500 watt inverters fail [one went up in smoke but didn't catch fire ] and the 12volt outlet on a solar controller shorted out letting a hot melted wire from the bed lamp drop down on my bed in the van.
  • BB.BB. Super Moderators, Administrators Posts: 31,758 admin
    With 24 hour power--The chances of both compressors starting at the same time (somewhere around 600-1,100 VA starting load per standard compressor) is usually pretty slight. With shutting down the inverter overnight, and cycling on--You are pretty much guaranteing that both start at the sametime and hitting the inverter with a heavy starting load at least once per day--That is certainly harder on the inverter.

    Other issues--Typically, the AC inverter has some large filter capacitors on the input--If you are killing the DC input, that means those filter caps get hit with a DC voltage spike every time you repower the inverter--Also not great.

    I would guess you are stressing the inverter a bit more with power cycling... On equipment that was powered 24x7 (such as computer servers), it was not "rare" for the AC power supply to fail when the service person turned the server back on after power cycling (did not happen often--But did power on failures did occur). So--If you had an inverter that was getting "weak" and near failure--The power cycling would possibly cause that failure to happen a bit sooner (failure was probably going to eventually happen eventually).

    Those are the typical issues on DC power cycling the inverter that I see. If you are using the inverter's shutdown circuitry--Then you don't have the DC voltage spike on repowering--So that would be less of a stress.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mcgivormcgivor Solar Expert Posts: 3,842 ✭✭✭✭✭✭
    Can't answer the question definitively  but I do have a cheap no name inverter that has been on for 4 years, it was recently shut down to change batteries but will remain on 24/7 in the foreseeable future.

    What I can say is if insects or geckos can enter an inverter, they can create havoc, I lost my first quality inverter to a gecko, stainless steel mosquito net over the holes of ingress solved that particular problem.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • PhotowhitPhotowhit Solar Expert Posts: 5,588 ✭✭✭✭✭
    Plucka said:
    ...and the 12volt outlet on a solar controller shorted out ...
    Sounds like you had the inverter connected to the 'load' output of the charge controller?
    This should NEVER be done. Most charge controllers warn against it. I've never found one that suggested it. Inverters should always be connected directly to the battery bank!
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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