• Naz@sh.itjust.works
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    8 months ago

    Hello, expert solarpunk here.

    TLDR: Car battery is 350Wh. Fridge uses 143W idle, so it’ll run a fridge for 2-3 hours.

    Explanation below:

    Car batteries are lead-acid (sulphuric acid and lead plates).

    They discharge according to Peukert’s Law as the negatively charged plate gets covered in lead via the acid (electrolyte).

    As the battery depletes, the negative plate can begin to take permanent damage, and so you can’t discharge a lead-acid deeper than 10-20%, or about 10.8V, with the safe limit being ~50% discharge.

    Most 12V, 60Ah batteries therefore only safely store and nominally discharge 350 Wh @ 350W.

    You can discharge that as fast as you want but the faster you discharge, the lower the capacity is (with 1000-1500W bringing you way down to like 65 Wh). Fridges have a surge when they start up to fire up the compressor. Starter batteries can take that, but once the refrigerant is cold, the fridge just maintains the temperature which uses a lot less energy - about 143W on average.

    • baru@lemmy.world
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      8 months ago

      Fridge uses 143W idle

      Isn’t that like 1250 kWh on an annual basis of idle usage? An efficient fridge should use 150-200 kWh per year, this isn’t just idle usage. Even an inefficient fridge would be really high with that kind of idle usage.

        • DogWater@lemmy.world
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          8 months ago

          No it doesn’t. Watts do give a shit what percentage is voltage vs amps. You have to convert between AC and DC as appropriate as well as ensuring the voltage of a 12v battery is stepped if needed, but the watts are the same in any case. (Not figuring for system losses)

          • genie@lemmy.world
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            8 months ago

            Congratulations, this is the worst attempt at ridicule I’ve ever seen

            • suodrazah@lemmy.world
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              8 months ago

              Your comment was ambiguous, stupid, and designed to ridicule. If you are attempting to imply inverter and other loss then be more specific. Regardless, the comment you were referring to already provides arbitrary values that you can assume include loss.

              So please explain to me what the fridge being 12v DC or mains AC powered has to do with anything, when an example uses arbitrary power and energy values? I’m genuinely curious.

              • genie@lemmy.world
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                8 months ago

                ooh getting aggressive now are we?

                I owe nothing to you. Enjoy your time being a sad person trying to bring others down on the internet :) I hope this little outlet makes you feel better

                  • genie@lemmy.world
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                    8 months ago

                    I’m sure the teacher of the high school debate team you’re on would be very proud ❤️

    • drathvedro@lemm.ee
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      8 months ago

      Fridge uses 143W idle

      The only thing running in idle is the timer and power led, which consume insignificant amounts of power. By my calculations, the average modern fridge does bursts of ~300W during compression and defrosting cycles, with ~40-50W consumption on average over long periods.

    • Aux@lemmy.world
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      8 months ago

      You have a very inefficient fridge! My fridge is rated for 272 kWh per annum, which is 745 Wh per day or 24 Wh per hour. You need to buy a new fridge.

    • HeckGazer@programming.dev
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      8 months ago

      You did not answer their question. They asked for Watts, not Watt hours. Average car batteries have a CCA in the range of 500 to 1000 Amps at 12V, so you could reasonably have 12kW in there :D