A better way

billybob9billybob9 Registered Users Posts: 141 ✭✭

I have an Off Grid and Battery System that I run a small Fridge with. I only want it on during the day as I have Blue Ice trays in it to keep it cold at night. This system is five 100 watt panel , 30 AMP controller, four 6 Volt golf cart batteries hooked in series, to make it a 24 volt DC system. I come off the 1st and 3rd battery posts to give me 12 volts DC for the 1000 watt Inverter that runs my fridge. The Inverter "Shut Off" has always been a problem and resetting to start is a pain in the butt. So I tryed putting a timmer on the fridge which helped some but on cloudy days the inverter would still trip off. To get around this I decided to use a 15 Amp Photocell with attached relay as a photocell will only turn on in the dark (dusk to dawn). After exploring ways to build one I figured out a way to do this that was much better. I plugged a power strip into my inverter then plugged 2 Dusk to dawn Photocell into it. On one of the Photocells I plugged in a 120 volt AC light. On the other Photocell I plugged in my fridge. Then I covered the light and the Photocell connected to the fridge with a box so no light from the outside would get in. It was all Plug and Play and took me 10 minutes. The Photocells were about $12 ea on the web and are working great ( On in the day and Off at night )....


  • mcgivormcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭

    Welcome to the forum

    First thing to change is the inverter tapping 12V from a 24V bank, this practice will ruin the two batteries being tapped as they will become undercharged and sulphated in a very short time. Either get a 24V inverter or reconfigure for 12V, personally I would recommend a 24V system.

    Running a refrigerator off grid really requires a system large enough to support it 24/7, maintaining a temperature is more efficient than allowing large swings, kind of like stop and go city driving uses more fuel than highway cruising. Even turned of for 6 hours will cause the temperatures of products within to rise above safe levels, milk will spoil in a couple of days. Many, including myself have experimented turning off for X number of hours overnight only to discover it really doesn't work.

    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: 5,729 ✭✭✭✭✭

    I totally agree with @mcgivor, drawing down just 2 of the batteries is going to create problems.

    You likely have most of what you need to create a 12 volt system, unless you are using a pwm charge controller with 72 cell (VMP between 35-39) solar panels. 4 GC batteries should be fine to run a small fridge 24/7 in most of the US.

    So tell us about the rest of your system, maybe we can help find the most economical way to setup a balanced system.

    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.
  • billybob9billybob9 Registered Users Posts: 141 ✭✭

    Thanks for the tip on tapping between terminals. I didn't know about that and thought they would just equalize. The Fridge is just beer and soda with no produce that's why I thought it to be OK.. I do have a 24V inverter but was just doing some testing with the 12V. Thanks again I like it here already.

  • BB.BB. Super Moderators, Administrators Posts: 32,331 admin

    Measuring your energy use too for your loads (AC and DC) is a big help too.... For solar power (and those of us living in California and Hawaii with "ridiculous" power bills), conservation is your first order of business.

    It is not unusual for somebody to by a "dorm fridge" thinking that smaller uses less energy... Only to find out that a dorm fridge uses 800 WH per day and a full size Energy Start rated Fridge/Freezer uses 1,000-1,500 WH per day.

    A refrigerator is usually the load that changes a system from a "small" off grid solar power system (500-1,000 WH per day) to a medium size system that can power ~3,300 WH per day (enough for a smaller/very energy efficient home).

    Using a Kill-a-Watt type meter for 120 VAC power, and even looking at the DC AH/WH meters for your 12/24 VDC power (if you have any DC loads) makes these tasks of understanding your energy usage much easier:



    And some basic test gear (highly recommend the DC Current Clamp DMM--Makes current measurements much easier and safer):

    https://www.amazon.com/gp/product/B019CY4FB4 (medium cost AC/DC current clamp DMM)

    https://www.amazon.com/gp/product/B07546L9RT (inexpensive "good enough" for our needs AC/DC Clamp DMM)

    https://www.solar-electric.com/search/?q=hydrometer If you are using flooded cell lead acid batteries--Always rinse with distilled water after use.


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • billybob9billybob9 Registered Users Posts: 141 ✭✭

    I've run this small fridge for about 5 years off this 24volt system with no problems and also used it to power small electrical devices. I just wanted it to be automatic and not require supervision. I have a 4k on grid solar system on my house but just wanted a small emergency system to play with. With the Photocells now controlling this system I'm totally automatic.

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