I reconnected things so the inverter cables are connected to DCDC side of the positive battery terminal and not to the battery side of the terminal fuse . I don't know what is the fuse size on the positive battery terminal (though it has a number 314 written on it, but 314A seems strange and too high). I know that the fuse of the DCDC is 250A and it supposedly can do 2000W.
When I pull 700W from the inverter (using the 2 x Jackery AC chargers), I measure 52A of current flowing from DCDC into the battery terminal area, with voltage around 13.5V. This means that nearly if not all of the power is coming from the DCDC and not from the 12V battery. This ran for about 10 minutes and I stopped the test. Note that while I am pulling 700W, the Jackery is only charging at 570W, so I am loosing 20% in this DC-AC-DC conversion process.
The reason why I have the Jackery in between instead of directly to the inverter is due to the following:
- In a blackout, my house will use an average of 500w of power for the most essential loads, but the load can be as high as 1800W for a minute, sump pump comes on while the furnace fan is running, lights are on at night.
- I don't want to pull more than 1000W from the car's 12V DC system, while the DCDC is capable of 2000W but the car may need some power for other stuff at any time. I have heard people connect 1500W inverter and the car throwing 12V system errors.
- In a worse case scenario if something bad happens, I want it to impact the Jackery and not the car, as the jackery is cheaper and is more built to handle unpredictable loads while the cars 12V system is not meant for this
- I already have the Jackery unit
The disadvantage of using the jackery is lost of around 20% efficiency as there is another DC-AC-DC step. And that your max average power is only 600W as that is the input limit of the Jackery unit. Use more than that on the average and your Jackery battery will drain.
The Jackery (or similar unit) provides such buffer as it can handle 1800W continuous or up to 3600w for a second or so. This keeps the load to the Tesla's 12V system a nice and stead 700W with the Jackery handling the spikes. My Jackery is not useful on its own as the battery capacity is too small at only 1.5kWh. So hence the car charges the Jackery, and the Jackery powers everything else. Note that there is a larger Jackery with 2kWh of battery and up to 2200W of continuous load, and can be AC charged at 1000w. If you are getting something for this purpose, I would suggest that instead.