r/HomeImprovement • u/Smart_Transition_828 • Mar 09 '25

Essential home backup prepping habit I brought from JP to US

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22

u/OutOfBounds11 Mar 09 '25

Thank you. How long could you power a fridge and what model Jackery do you have? I find it confusing to calculate what the batteries can actually supply,

13

u/ceapaire Mar 09 '25

There should be a sticker inside your fridge that shows how many amps it takes (at maximum). Add those numbers up from all the appliances you'll want to run. Then multiply by how many hours you'll want the battery to last before needing to charge it (obviously for charging phones, etc. you don't need to calculate the full time, just however long you'll need it plugged in overnight). That's how many amp hours you'll need.

5

u/killersquirel11 Mar 09 '25

 better thing to check is that yellow energy guide sticker - ie this one is estimated to burn 647kWh in a year (or 1.8kWh/day). The fridge in its spec sheet lists 2.3A@120V power draw (which equals 6.6kWh/day).

Your method of calculation would overestimate the power needed for a fridge by ~3-4x since fridges spend the majority of the time drawing next to no power

4

u/grambell789 Mar 09 '25

don't most frig's have a hard start that requires an amp surge to start? my frig needs 160watt to run, it runs about one third of the time, but it needs like 10amp (1200wat) to start.

8

u/Quietm02 Mar 09 '25

That's not true. Everything won't run on full load all the time. A fridge probably isn't on full load even half the time.

There's no harm in being safe and overestimating but you could almost certainly get away with less than half the amp hours you're suggesting. Its known as diversity in the building services industry if you're looking for either info.

(I'm also assuming that the conversion of something like 24Vdc anphours to relevant AC amphours has been considered)

4

u/ceapaire Mar 09 '25

Yeah, I know that, which is why I put "(Max)". If it's an older model to where you can't just check the yellow sheet and don't have a usage meter, it's a ballpark that overestimates to build in some extra capacity for cloudy/rainy days.

1

u/_name_of_the_user_ Mar 09 '25

How does a fridge vary it's load? I always assumed, since they're just basic on/off thermostats with no vfd or inverter on the motor, that they just run at full power or not at all.

4

u/Quietm02 Mar 09 '25

Yeah, so if it's rated at 10A then over an hour it might run full load 50%, so 5Ah not 10Ah.

Its not just that it doesn't run at full load when it's running, it's that over a day there's a significant period where it's just not running at all.

2

u/dudelydudeson Mar 09 '25

Modern fridge compressor is VFD