It's already connected and my prototype works well. There is still design refinement to be done, as well as optimizing it for cost and manufactureability. Until the design is closer to production, I'm hesitant to release too many details other than to gauge interest. One design target is that it be easy to install and remove, so the connection to the car is done by connectors in a safe and easy manner, and only takes a few minutes to have it operational.
I'm not worried about Tesla voiding my warranty, because I only tend to use it occasionally. It will have no noticeable impact on battery life, as most of my use scenarios will be very low average power. (Such as powering a laptop while driving, maybe running a portable vacuum to clean the interior once in a while, etc.) IANAL, But under the Magnuson-Moss Act, Tesla must prove that my aftermarket equipment caused the need for repairs before it can deny warranty coverage. So for example, if my Drive unit fails (my biggest concern), they would definitely not be able to say me drawing some power from the HV system caused it. Tesla builds a great car, and the battery packs seem to be very reliable and long-lasting. A few hundred watts of transient additional load is no different than say, running the heater or the A/C. (and in fact, will have way less impact!)
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I'm not going to talk about the internal design yet, but right now it's single-phase output only, but it can be easily set for 120v 60hz or 230v 50hz. In theory, 2 could be stacked for split-phase output, but I do not intend on targeting this use scenario. Right now my targets are: high-reliability, low cost, compact, and easy/safe to connect. Because of it's small size, it will not be able to sustain high output for long periods (thermal limit), but it will be able to say run a full-size fridge/freezer and a few other appliances in an emergency. I've successfully used it on a long road trip to heat up meals in a microwave oven which was fun and convenient. I've also ran a bright DLP projector for a Tesla "drive-in" movie. =)
The new documentary "Racing Extinction" features a Model S equipped with a commercial Christie 4K Digital Cinema projector which I set up to run from the HV system:
Check Out This Modded Tesla Model S (images + video)