CHAdeMO V2H – Home Power Backup

Ever since modern, commercially produced electric cars starting coming out in 2011, there has been talk of using them as power backups. There have been a hand-full of products out there, but with limited availability, prototype only, or non-U.S. power specs.

So, I thought I’d try my own.
On my 2012 Mitsubishi iMiEV electric car, there is a DC Fast Charge port which uses the CHAdeMO interface. This was the first fast charge standard, created by Japanese car companies. It allows for direct access to the high voltage battery pack so that an external 500VDC can quickly charge the car.

Because that’s direct access to the battery, power could also be DRAWN OUT from the battery! This would be very useful for powering a home during a blackout.

Electric car batteries are generally around 360 volts. Home power battery backups – usually combined with solar systems – are typically 12, 24, or 48V. Those voltages are generally considered “safe” to work on, and there are many inverters which will run on those voltages.

On the other hand, on-grid solar inverters need to be able to handle the voltage of a whole string of solar panels in series. Panels are generally around 30 volts each, so 10 solar panels would be 300VDC and 20 panels would be 600VDC! Because of that, on-grid and hybrid solar inverters can often handle up to 600V, although the battery packs for hybrid inverters still usually max out at 48V nominal.

So, here’s my thought – run an electric car battery into the SOLAR INPUT of a hybrid inverter. (A hybrid inverter does NOT need a grid connection, so it would be the right type needed for power during a blackout.)
If an electric car battery is 360V and the inverter can take in up to 600V, it should be easy, right?

Well, it’s a little more complicated than that…
This project is actually 2 parts
1) Get high voltage power out of the car
2) Convert it to 120/240V 60 Hz AC power for home use.

Let’s focus on that first part, getting power from the car.
An electric car has plenty of safety features on it. One of the biggest is simply that the high voltage in the battery is NOT available anywhere on the car. I can literally LICK the high-voltage DC Fast Charge (CHAdeMO) port and be fine. The reason why is that there are high-power internal relays (known as “contactors”) which turn on and off the power to the port from INSIDE the battery pack.

The controls to activate those contactors comes from both the car AND the DC Fast Charger. Signals pass back and forth between the two over CAN communications. After a series of quick tests, both the car and the charger activate analog 12V and ground signals which together activate the power. With the power connected, the DCFC can then charge the car.

Since it’s actually the analog signals that activate the power, I figured that I could simply imitate those to power on the port. The good news is that somebody has already figured out how to do this on the car side on a Mitsubishi iMiEV.

In the iMiEV, there are some car computer parts under the back seat. Removing the seat and a metal cover reveals these parts, including the Fast Charge Relay. This is the 12V relay that would normally be activated in the car after the CHAdeMO CAN information going back and forth. Instead of using some complicated data to activate this, it can be done manually by simply jumpering together two of the pins in the relay connector. Even better yet, a simple switch could be connected there and mounted to the dashboard.

This relay provides positive power to the coils of the internal contactors.
The other end of that circuit is on the DC Fast Charger side. It’s simply a switched ground connection. Grounding then completes the circuit, the contactors close, and power is available at the CHAdeMO port.

So, how do I complete that circuit and physically get the power? 3D printing to the rescue!
To purchase a CHAdeMO male connector is very expensive. When they first came out, they were about $3,000. Nowadays, they can be purchased through places like AliExpress, but still cost around $1,000.
I found that on Thingiverse, somebody had already created a 3D-printable CHAdeMO male connector.
This is several different pieces that screw together, and it requires making a number of signal pins and two high-power pins for the main power.

I had a friend make the 3D prints for me. (Kudos to Pete, Josh, and BrownDogGadgets) Once I had the parts made, I set to work creating the pins that would go inside. That meant some mail-order electronics parts and a visit to a metal shop. After a fair bit of experimenting, I had 1.5mm electronics contacts soldered to 1/8″ brass rods for the signal pins, and some 9mm solid copper cut to length for the main power pins. I even nickel-plated the copper and added a 600V semi-conductor fuse right in the handle.

For my power cable, I used some 600V SOOW sheathed 3 conductor 12 gauge material. 12 AWG is commonly used for 20 amp circuits, but keep in mind that 20A at 360V is over 7,000 watts! That’s far more than is needed to power my entire house!

For the signal wires, I just used some LAN cable I had around. That has four pairs of wires inside. Seeing as how CHAdeMO has a total of 7 signal wires, that’s just about perfect. Several of those pins are just ground, so I connected them all together, including the wire going to the top-most pin of the charge port, which is the vehicle ground. On a scrap electrical box, I added a pair of switches. One would be for positive 12V power from the Charger side (which it turns out I don’t need, as the under the seat relay hack takes care of that,) and the other one to ground Pin 7 to complete the circuit and turn on the contactors.

Testing for fit. Note networking cable wire going to signal pins.
High-Voltage power was never activated without connector being completely assembled.

I put my multimeter on the far end of my 3D Printed CHAdeMO connector, turned the car on (with the relay hack jumper in place) and turned on the ground switch. At the multimeter, sure enough, it showed 360VDC. I had successfully activated high-voltage power at my DC port!

WARNING: BATTERY PACK VOLTAGE IS LETHAL. DO NOT TRY THIS AT HOME.
Needless to say, a person has to be very careful around this sort of thing. 360VDC has the potential for shock, arc flash, and all sorts of ways to injure or kill a person. I was doing this in good weather, without touching the connector, had a fuse built in, was not providing any load, etc.

Before actually using the 3D printed connector for providing real power, I need to do some work properly sealing it up, potting the pins, and making sure it is solid, water resistant, and shock-proof.

Now back to 2)
How to convert that power to AC?
I’ve looked at a number of different solar hybrid inverters. However, most of them DO require at least a small 48V battery pack to operate. Also, I really couldn’t find any information on other people who have successfully run battery power in through a Photovoltaic (PV) input.

In my search, I found that some people were experimenting with SolarCity H6 inverters. These were made by Delta specifically for SolarCity and the original Tesla PowerWall – which was a HIGH-VOLTAGE battery pack!
Unfortunately, you can’t get these battery packs, nor is there any warranty or support for these “orphaned” inverters. The good news is that they are CHEAP!

The most interesting aspect of the inverters is that they can be used OFF-GRID by only connecting solar to the PV inputs – no battery pack needed!

So, I ordered one.
Signature solar has plenty of these inverters as new old stock for good prices. I found another one on eBay, which was used, for only $325 + shipping and tax.

Here I am just after receiving the inverter.

The plan at this point is to feed power from the car, through the CHAdeMO connection, to the PV input of the inverter. When I opened up the inverter, I did notice that the battery input has a pair of 600VDC fuses, but the PV input does NOT! I assume that this is because a battery can create a tremendous amount of current, while solar panels can’t. Even if you have 20 panels in series, the voltage will increase to perhaps 600 volts, but the maximum current will only be (in the case of the solar panel at my house) about 8 amps.

So, I may have to add some fusing to the PV input. I also plan to add a pre-charge circuit. This connects the high voltage “more slowly” by first running it through a resistor. This helps prevent arcing when contactors or DC disconnects are closed and protects internal capacitors.

Last time I went past a public CHAdeMO station, I stopped by to take a look at how the commercial connector compared to my 3D printed connector.

2022/05/15 –

I started assembling the parts onto a piece of fake wall on casters. I have a resistor and contactor from a Nissan Leaf as a pre-charge setup. There’s also a pair of fuses now on the PV input where I’m feeding power the H6 inverter from the CHAdeMO port. (There’s also a single fuse hidden in the CHAdeMO handle itself.)