My DIY battery backup solution for my house is now online! Here’s an overview of the completed system. (For the full story, start with the linked blog post.)

The Generac transfer switch is at the top (1), wired into my electrical panel which is out of view on the right.

The 12V power supply, with a battery backup (2), is below the transfer switch. It’s powered by either utility or backup power, but has a small internal battery so it can keep the controller running while it’s deciding whether or not to switch to backup power.

The controller (3) takes 12V in and has a 5V power regulator for the Adafruit Feather M0 microcontroller that runs the whole thing.

The Ecoflow batteries (out of view below this photo) are charged by two Meanwell 36VDC power supplies (5) which are wired into a single control switch (4) for convenience. The 36V output of the power supplies goes to the solar panel input of the Ecoflow batteries, and is currently limited to 8A through settings in the Ecoflow control app, which puts the total power well below the 600W output of each power supply. If needed, I can increase the current for long-running outages when I’m charging the batteries with the output of my Ioniq 5 V2L adapter. I picked 36V because I wanted each power supply to max out at about 600W, so at the 15A maximum current the batteries can draw, 36V gets me to 540W which is close enough.

To be able to automatically switch over to battery power, the Ecoflow batteries and 240V voltage doubler unit must be powered on all the time; they do draw a not insignificant amount of power to stay on, so they periodically recharge themselves from the “solar” power input. I measured the power draw with a Zigbee power meter, and I’m getting about 90% efficiency based on the power in to the Meanwell DC power supplies vs. what the Ecoflow batteries report as the input power they are receiving, which is not too bad.

Since I have plenty of excess power from my solar panels, I’m not too worried about efficiency at the moment, but eventually I will look into whether I can turn the Ecoflow batteries on only when needed. Apparently they have a CAN bus interface to the remote control unit (which I have), so that will be another project to reverse-engineer the control protocol and have my backup power controller use that to turn them on and off.

I’ll post another separate update with details of how the controller decides to switch to backup power, and how it controls the transfer switch.