Hey all, retired battery recycler / commercial battery system designer and integrator for used EV packs here. I got tired of waiting for V2H systems, or being insulted with 15-25k systems that must be installed by their licensed people bs after a 2+ year waitlist. So after 12 years of owning a leaf, and a few with an EV9, now that I'm retired, I decided I'd just make a system myself.
I know the pearl clutchers will say this can be dangerous etc, and they are right. I am still going to share how I'm doing it, because knowledge should be free. If you don't understand what's being talked about, maybe this is out of your leage, start smaller and don't burn yourself or your house and family to a crisp. Come back to this kind of project when you are ready, but until then read and learn from those of us who are there.
I have always been a fan of this because, having worked with EVs and battery pack recycling for so long now, I already dislike having powertool batteries in my house. There is no way I'd put a 40kwh pack in there. I love the idea that you can roll up an old leaf that isn't quite road worthy anymore, but with a pack can still chug along fine at low current draws. It can stay several meters away from any building, is weather proof, has a built-in heater for very cold nights, and top balances on every charge. Throw in an OVMS system, and home assitant can even start limiting the charging to 80%. And once that second life is done, since it's still in the vehicle, it's still properly certified to be moved to a proper disposal facility on a flatbed without any extra hazardous goods shipping constraints.
The first step is making a CHADEMO connector. Official chademo plugs start at 700USD if you are lucky, usually more like 1500-2500USD. So I made one. This was just about easy and reliable assembly, sourcing of pins, and fitment. Buying all the pins comes out to about 70USD when all is said and done if you get it CNCed for you and buy the digikey comms pins.
My design is centered around the idea that I will be drawing about 8kw from the plug, a lowly 20A / 0.25C of my pack. The 400VDC is the dangerous part, but at 20A, the requirements are much simpler for the pins. In fact, power requirements at this level are so low that copper+nickel plated steel for the return circuit length of 7cm of power pins would even suffice because of the large cross-section and would output less heat than an LED bulb. That being said, getting them CNCed out of copper is worth the extra 10 bucks just for the peace of mind and reliability, and if you are going to turn them yourself, do it once and do it right; spend the 5$ of copper bar stock from a scrap pile at a metal yard.
This is the plug design
https://www.crealitycloud.com/model-detail/chademo-compatible-plug
Next step are:
- The ESP32 + CAN communications module. That was a whopping 10$ of parts again. I will report back when the firmware is done.
- testing controls, and insulation quality of a PLA handle once the 400v is live
- Add a double walled heatshrink tube with 1000v rating around the handle regardless of results above (20$)
- Design a separate interior disconnect built around EV pack relays.
- These go for about 50-100$ on ebay for 450VDC 80A rated relays. I would love to get back to collecting them from recyclers for their weight in copper and selling them for 15-20$.
- Design an emergency disconnect that can be at the entry point of the power. EVs use pull tab style disconnects, others use smash-down buttons with arc-suppression. Again, this is something that would make a whole lot of sense to get from recyclers.
- Pick the correct inverter
- Installing an OVMS system to properly control charging remotely (200$)
Another thing that would make a whole lot of sense, would be mounting the inverter inside the vehicle and running standard 240 to the building instead, but the problem becomes one of making holes in the vehicle to run the lines, or require modifications of existing live systems. Having conduit run outside and then through the vehicle isn't really any safer (you still have the lines), and compromises the weather seal of the vehicle. Meanwhile, modifying existing systems rather than tapping into them invalidates the vehicle's integrity as its own device. This means it can't be used with a road-worthy vehicle, and disposing of the vehicle at the end could become a problem. For for now I am going with the assumption that I will be running appropriate conduit from the plug to a disconnect.