Tesla V2L – Vehicle to Load

Teslas are great cars. But there’s one thing missing – Vehicle to Load, (V2L) the ability to make use of some of the battery storage as AC power, whether it’s for camping, emergency situations, or however else you would want to use it.

Not long ago, I purchased a non-running 2013 Tesla Model S and fixed it back up into running condition. (See the video playlist here: https://www.youtube.com/playlist?list=PLmHss3DBZUilyh1YTMvIbLa-QSTeUjIdY)

When I was troubleshooting the lack of Supercharging after the repair, I had removed the back seat and examined both the On-Board-Charger (OBC) and the High-Voltage Junction Box (HVJB). I noticed a couple of things. One was that there is an empty space under the seat. The Model S had the OPTION of a second charger. That empty space is where that would have gone. Not only is there that space, but there are also connections for that second charger already inside the HVJB as well as a removable plate to access them.

What if instead of adding a second charger, I instead used that space and connections to add an INVERTER?

The inverter would have to be able to take in 400VDC and output 120 or 240VAC. There’s not much out there for affordable “off-the-shelf” units that meet that description. In fact, internationally, 240VAC is much more common than 120VAC, and the more of something that is manufactured, the less expensive it tends to be. After looking around a bit, I located an inverter “bare board”. This is just the part of a complete inverter which actually does the work of converting DC to AC – it does NOT include cooling, a case, fusing, outlets, etc. Although it’s a 240VAC board, a small potentiometer on it allows for adjusting the output, including all the way down to 120VAC.

Once the slow boat finally delivered my package, I was able to start experimenting with it. I used a rectifier to convert 240VAC wall power into 330VDC power as the source for the inverter. Sure enough, I was able to power it up, adjust the output, add a cooling fan, and power some basic AC loads.

I’d still need some safety features and eventually an enclosure. I ordered an AC breaker and a pair of DC “touchless” fuse holders, along with some 10A DC Solar Fuses. Solar equipment is commonly 300-600VDC, so it tends to match up fairly well with the requirements for electric car battery packs.

I was trying to decide what would work best for an enclosure. Digging through my shop, I found an old 48V inverter which somebody had given me because it was broken. I checked the size, and it looked like it would fit under the back seat of the Tesla. I disassembled the case and removed the blown power board and cut out most of the wiring. Since it just happened to be an inverter case, I could reuse the outlets on the front of it and the fan locations. Unfortunatley, the fans were the wrong voltage, but I could easily swap them out for 12V fans, supported by the board I was using.

I mounted the inverter power board, breakers and fuses, and updated fans all to the housing. I connected the output to outlets and power terminals on the front of the case.

The next trick would be to connect it to the High Voltage Battery Pack of the Tesla.
Inside the HVJB are the Supercharger contactors, high-voltage bus bars, connections to the charger(s), a couple of fuses, and the output to the DC/DC converter. I decided to make the connection at the DC/DC terminals, as that was immediately AFTER a HV fuse, and the size of the cables was appropriate for connecting 12 AWG wires to the inverter. I bought several feet of SOOW cable from the big box store. That cable has a heavy-duty rubber jacked and is rated for 600V.

Because of the high-voltage inside the junction box, there’s a safety switch on the cover. If you remove the cover, it automatically shuts down power to the High Voltage Battery. That’s great from the point of safety, but how could I get my cable through without drilling holes if I can’t leave the cover off?
On the side of the HVJB is a small removable plate. That takes up the space when a second charger is NOT installed. I removed that plate and essentially made a copy of it. I traced it onto some heavy aluminum and cut that out, matched up the holes and added some mounting bolts. I could now drill a hole in my COPY of the side plate, add a rubber grommet, and run the cable through.

Inside the inverter case, the DC conductors goes through both DC fuses and then to the input of the inverter. From a “big picture” point of view, the inverter case should now ALSO have a High Voltage Interlock switch on it, and that’s one of the things I still need to work on.

To output the AC power from the inverter, I’ll need some electric outlets. I was originally thinking that I wanted one in the back seat and another on the outside of the vehicle. I didn’t want to cut away any of the interior of the car, and I think a surface-mounted electric box would just get in the way of somebody’s feet in the back seat, so just the end of an extension cord would be the simplest way to go. I bought a short extension cord and ran it through a hole in the car body so that the female end would go under the carpet and come out by the back of the driver’s seat. This allowed some slack to move the cord as needed and keep it out of the way the rest of the time.

For the outside power outlet, the first thing I would need to do is decide where I wanted to put it. Some other electric car brands re-use the charging port, just plugging in an adapter which has an outlet on it. Besides being such a clean-looking solution, that also means it automatically prevents the car from being driven while something is plugged in to the exterior.

The connections to the charging port are easily accessible inside the HVJB. It would be easy to connect to them. The issue is that the SUPERCHARGER system connects to these exact same bus bars! I would need to add some additional HV contactors to DISCONNECT the inverter while Supercharging. Even then, there’s the possibility of a failure of those contactors or other issues which would mean high voltage going to the wrong end of the inverter. The most likely result would be a fire under my back seat!

I do love the LOOK of the charging port on the Tesla. It’s well-integrated into the vehicle by being hidden under the drivers-side taillight reflector. Perhaps instead of a charging port, I could have a power outlet on the other side? I had already removed the passenger-side taillight and saw that the reflector on that side has some extra room under it. If I replaced that reflector with a 3D-printed part which could hold an outlet, I could make the whole thing look pretty stock!

I began working in CAD, using the free version of Autodesk’s FUSION software. I took a scan of the reflector, as well as measurements with a calipers and started modeling something that would fit the same space. After creating several versions, I finally had a main component that would mount to the taillight and a hole in the car body. I mail-ordered a single outlet and some “push-to-open” magnetic catches. The completed assembly would hold the outlet and have a place to mount the magnetic catch. An 1/8″ rod would act as a hinge pin and attach a cover. That cover could open 90 degrees to reveal the outlet – similar to the charge port on the other side.

Once I finally had a good print and all the parts mounted correctly, I still needed the reflector cover. My scrap materials include an old (legally-obtained) STOP sign. I already used a bit of the material to make the side cover for the HVJB. This time, I would also take advantage of the fact that it was already red and reflective! After cutting, some grinding, and then repeating test-fitting and more grinding, I had a reflector which was a pretty good match for the original. I attached it with clear butyl tape.

Now, I can push on the reflector, it opens to reveal the outlet, and that has it’s own cover as well. I figure that combined, it should help keep out the weather!

To connect the outlet to the inverter, I made use of an old 12 AWG extension cord. The one end was damaged and needed to be replaced anyways. So, I cut that off and measured how much I would need in the car, then cut it to length. The AC power cable simply follows wiring that’s already in the car and will be fully hidden behind the seat and trim.

Of course, the battery main contactors need to be ON for the inverter to work. My observations so far are that they are on pretty much any time you are doing ANYTHING with the car. They turn off (car in “sleep mode”) after about half an hour. Since both KEEP mode and CAMP mode allow keeping on the HVAC for extended periods, and that’s powered on the High-Voltage side of things, it looks like if I want to use the inverter for any extended amount of time, all I need to do is put the car in one of those modes.

I ran a few test loads.
I have an electric space heater with low/med/hi settings on it, and ran that at 1300 watts for about 3 hours. The car and inverter had no problems at all with it. The air coming out of the inverter was slightly warm, but that was it. I also did some load testing with an electric water kettle. That also worked great. Running both as the same time, I expected that I would pop the AC breaker, but instead found that I hit the upper limit on the inverter instead. At right around 2,000 watts, the voltage drops suddenly to about half. The inverter bare board was rated at 4,000 watts, but I always figured that was the power measurement running at 240V, and it would really be current-limited, so that would mean around 2,000 watts at 120V.

That’s it for now. This is a current project, and I will update this page as I work on it.

I still need to work on a few other things, including:
• HV Interlock switch on inverter case
• Does it need a pre-charge circuit? If so, build one
• Main power switch for inverter – right now, it’s always on
• Voltage switch for inverter – can I make it easy to switch from 120 to 240 and back?
• Physically mount down the inverter using Charger mounting points (easy, just haven’t done it yet!)
• Graphics and labels – warnings and I.D.s on inverter case and inside outlet flap
• GFCI
• Anti-drive-off circuit for exterior outlet
• Outlet in the Frunk?

As I work on those, come here again to check on updates, or check out the coming videos on the YouTube channel!

Until then, stay charged up!
-Ben Nelson