Hey all-
Just tuning into this thread. I have a lot of thoughts here:
1. I don't know how bad the Challenger panels are. I know Zinsco and Federal Pacific and Challenger are all on the "bad" list, though I believe some of the issues were with bad breakers and other issues were with bad panels in addition to bad breakers. There are 3rd parties that sell new breakers for Challenger panels that are presumably safe today (but I don't know if the underlying panel might still have issues).
2. Knowing what I know now and with the skills I have, I likely would replace that panel inside your condo with a new one regardless of any EV project. The actual parts are stupid cheap for such a simple panel. Like maybe only a couple hundred bucks? Since it is inside your unit and presumably owned by you, I don't think the HOA could have anything whatsoever to say about it. I would install a new one that was capable of at least 100a or 125a (if not a full 200a).
3. Can you take the cover off that panel and take detailed pictures? I need to know what size (AWG) of wire feeds it, whether it is copper or aluminum, and what kind of wire it is (SE wire, THHN, XHHW, etc...) - I am wondering if it is in conduit all the way back to the main panel - it looks to me like the four units that feed out of that main panel are in flex conduit going down out of the panel and so if you are really lucky it might be conduit the entire way (like underground). If so, we need to know what size the conduit is. It is possible that say the existing wire is aluminum and that you could just pull in new copper wire with a higher ampacity into the existing conduit (or simply larger gauge wire than the previous wire but in the same conduit). Also, please post a detailed picture of the sticker on the door to your existing panel. I need to verify which breaker types are allowed in the panel.
4. The HOA board should have capital reserve funds for projects like replacing those main electrical panels - this is a longer time horizon project probably, but if those panels are deemed unsafe then the HOA board is obligated to replace them (assuming they own them which I am sure they do as they are common services). 70a per unit is simply not enough for modern needs. (note that the future involves us stopping burning natural gas too and so more things will shift to electric)
5. If a licensed and insured electrician is willing to add a 30a 240v receptacle for you off that existing panel and they are able to find you a breaker to do it with your existing panel, then I might be tempted to do it. The install should be relatively inexpensive as it is such a short run and getting "something" to tide you over is the most important thing right now. I am not sure if anyone makes a Challenger compatible quad pole tandem breaker that is 30 + 30 @ 240v each. That would be the only way to add another 30a circuit I think (double up the AC breaker). Note that Eaton cross-rates their breakers to work in a huge range of other manufacturers panels, but I am unsure if the Challenger ones are compatible.
6. Doing a transfer switch on the AC unit is not a horrible idea. That would certainly solve the breaker issue and load calculation issue. Though I would not want to put an EV load on a questionable breaker if indeed your Challenger breakers are potential hazards. I might swap the breaker out with a modern replacement at the time I did this (if not swapping the entire panel). Though you will need hours of charging a night (depending on your driving needs) and I personally would not want to be without AC. Actually, how many miles a day of driving do you need to plan for? We should have started there.
7. I would probably in addition to replacing the panel, I would get a Sense home energy monitor (I have one). This would let you track your usage to see how close to that 70a limit you get. My guess is your loads are pretty light. I would absolutely not want to live long term with only a 70a feed - your HOA needs to come to grips with that - folks are going to need upgrades as EV's become mainstream!
8. I am also a massive fan of the Wall Connector. If I replaced the panel I would probably put say a 50a breaker in the new panel and wire a Wall Connector up with sufficient ampacity wire for say at least a 60a circuit (48a usable). Then I would set the Wall Connector down lower (using the rotary dial inside) than the full 50a circuit allows for in order to stay within load calculations. In the future when you finally get a 125a feed to your unit (or whatever) you could just dial it up as needed (and maybe swap the breaker up to a 60a breaker). A huge value of the Wall Connector is that it has small increment steps so you can dial in how much calculated load you have available.
Please don't let this scare you away from owning an EV! You are so close! I *love* my Tesla M3! I went overkill (because I could) and installed a 60a circuit and a Wall Connector. I only have a 30 mile commute total round trip. My car charges in an hour every night when I get home. It is insanely fast and overkill. Even 20a (16a continuous) at 240v might be sufficient for your climate and driving habits!
Note that I need to call out that some have mentioned charging at night means things won't be an issue, but this is not how code works. NEC does not rely on layman humans to provide safety by remembering to set the charge timer. It assumes the users are not capable of avoiding overload situations. Doing load calculations is one layer of safety and the actual overcurrent devices are another layer of safety.
Check out this panel you could replace yours with:
Eaton BR 125 Amp 12 Space 24 Circuit IndoorMain Lug Loadcenter with Cover Value Pack (includes 5-BR120)-BR1224L125V1 - The Home Depot
It has 12 positions vs. the eight you currently have. Each one is rated for "tandem" breakers which means you could have up to 24 circuits. It is rated to be fed with up to 125 amps of feed capacity in from that main panel. $42.95 including five 20a 120v breakers! (though you only need three currently) That is insanity cheap. Unbelievable. If I were you I would go out and buy that panel (or I might even buy a larger / higher capacity one than that) and replace your existing panel today. Zero reasons to have any safety concerns with the panel in your house. That looks like probably just a few hours for a professional to swap.
Good luck! Please report back! (and have a great trip!)