On paper, you can look up an appliance’s load, or look at it’s nameplate. My fridge says 11.6A & it’s in the sense detected device topic; model PSS28KSHSS
Traditionally 12A x 120VAC = 1440W is how you’d calc backup generator or inverter size. Address peak load later. We’ve had power outages & would like to avoid throwing groceries away. Also, be able to use the fridge normally during an outage. Generators do not match output to load well & come with many disadvantages. An inverter matches perfectly & has other advantages.
An electric car with a 12VDC battery can power an inverter. Find the rating on 12VDC charger, ie 1000W. Can I power my fridge? Traditional calc says NO, 1440 > 1000.
Use Sense to show YES. Add a smart plug like Kasa HS110 to measure total load of fridge. Sense alone may not find all the fridge components so it would show partial load. You could move the C clamps to your fridge circuit. Let the smart plug feed data to Sense for graphing for as long as you want to simulate a power outage; 4 days for me.
From 9:45AM Tuesday to Saturday, smart plug recorded many 64W cycles that I assume is the compressor. Sense also found this, I could hear it & named it Fridge. For the 1st time I also saw 2 600W loads I assume is the defrost. Sense had found a 364W load I named Fridge 2 but I didn’t confirm. 3W is standby.
Sense + smart plug shows I can power & use the fridge normally during a power outage. A pure sine 800W inverter + extension cord + maybe a towel under the window is all that’s needed. 1600W should be the peak rating.
A 1000W inverter would let me power other loads & is the max the car supports. Repeat Sense + smart plug for any appliances you need during a power outage. 90W circulating pump keeps house warm, etc.
So why are experts (1 EE, 1 Mech E) saying “that can’t be right”? Sense alone or + Kasa are missing the startup peak. I expect >1000W then 64W tail, which does seem low. Do I have an induction compressor? I don’t think so. I trust Sense & Kasa are accurate enough to size the inverter. Doing so provides a big advantage over starting the gas emergency generator. If there’s an error; please let me know.