this post was submitted on 18 Mar 2024
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[–] [email protected] 143 points 9 months ago* (last edited 9 months ago) (6 children)

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.

[–] [email protected] 41 points 9 months ago (1 children)

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.

[–] [email protected] 18 points 9 months ago (1 children)

I don't know.... you didn't mention your uncle once...

[–] [email protected] 4 points 9 months ago (2 children)

That's because he is his uncle. You're seeing the source material, be amazed

[–] [email protected] 2 points 9 months ago (1 children)

Does... Does he work at PlayStation?

[–] [email protected] 1 points 9 months ago

It's a secret. You'll have to ask his uncle

[–] [email protected] 8 points 9 months ago

Wow, those are some serious Licensed Insurance Agent skills

[–] [email protected] 4 points 9 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.

[–] [email protected] 3 points 9 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.

[–] [email protected] 2 points 9 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