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this post was submitted on 18 Mar 2024
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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.
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.
Watt hours are watt hours. Sure the compressor won't run on 12 volts as is but the energy is there, just needs a converter.
Fwiw, our 15 year old fridge uses around 1000Wh per day.
That's a big joule thief
Sure, buy an inverter and burn up 10% of your energy in the conversion if you're lucky. That inverter will cost roughly as much as the contents of a standard fridge + freezer, by the way :)
At that point just buy a well insulated cooler and always have some ice on hand. It'll last much longer.
The question wasn't "Is it efficient or cheap", it was how much energy is in a battery, and if and for how long would it run a fridge. If you also want to add one more point to why you probably shouldn't do it, car starter batteries don't generally like to be deeply discharged, you'd want to get a marine battery for that use.
As for how much the inverter would cost, depends on the fridge, but Amazon has a 1000W inverter for around $85, that should be enough for most. Ours could run from a 300W one, they cost around $30. Pretty handy devices if you want to run any kinds of electronics from a car anyway, I have one for when I want to charge my laptop and RC batteries on the field.
3500 watt inverter is 300 dollars at a Flying J. Mines 7 years old and was used 5 years straight when I was a trucker, as I removed the 12v factory fridge that could kill 4 batteries over night, with a 110v fridge, I could safely leave food in all my days off and the truck would still start. Now it's hardwired to my pickup as a emergency generator and electric impact wrench power source. People laugh initially when they me pull out the impact and then ask what it cost. I also mounted a coffee maker behind the seat because gas station coffee is fucking garbage and its 4 hours to a major center
Energy is energy, you are not an electrical engineer.
Congratulations, this is the worst attempt at ridicule I've ever seen
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.
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
Ad hominem dodging of the question. Classic.
I'm sure the teacher of the high school debate team you're on would be very proud ❤️
Much like your current high school physics class.
No answer? Ok, you're just sad that your comment was dumb lmao jeepers
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)
You should Google what a step up and step down transformer do. It's very simple and easy to prove you're a dipshit once you understand you're arguing from bad faith trying to compare a simple bit of circuitry design to hydro power.
https://youtu.be/GtTcuexjeRw?si=e1p0nUHh1uXBp24R
3 seconds of googling like I said
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We are talking about whether it's possible to run a regular fridge on a 12v car battery. Not if it's efficient lol. You have to convert DC to AC because that's part of the problem, so yeah I made that jump all on my own lmao
You're a troll, but there's no rustled jimmies here.... You're too obvious.
No you didn't lol
I don't know.... you didn't mention your uncle once...
That's because he is his uncle. You're seeing the source material, be amazed
Does... Does he work at PlayStation?
It's a secret. You'll have to ask his uncle
Wow, those are some serious Licensed Insurance Agent skills
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.
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.
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