I'll be visiting my father come May, and he lives in a supercharger desert. His laundry room is right next to his garage & his dryer has an L6 outlet.
L6 is a category, so it doesn't really identify the outlet. That first part, L6 are locking plugs that are for the 208V or 240V levels. But there would be a second number that identifies how many amps the circuit is. So it would be something like an L6-20 or L6-30, etc.
Let's say I bought one of
these aftermarket adapters - even
if his outlet was on a 30A braker, I'd have to dial the car back down to 16A, since the adapter is rated for 20A & I'd have to account for the 20% overhead, correct?
Or let's say don't. I don't recommend adapters like that for that kind of reason you are getting at. The Tesla adapter part announces to the car how many max amps, so if you are using the 14-50 Tesla plug, it is going to think it can use the max 32A that the UMC can do. And as you point out, if the circuit is really a 20A or 30A, you would need to manually adjust that in the car to the 80% value.
But that's just not all that good. The car is supposed to save that setting according to the GPS position at that charging location, but that is not always reliable. Exact case in point: Just this week, I was driving home, and I noticed that on the map it was showing my car several blocks off from where I actually was. It wasn't a big deal because I wasn't using navigation, so I didn't think much of it. So I got home and plugged in and went inside. About an hour later, I opened up my Tesla app to check on something, and I saw that the car was currently charging at 40A. That was not supposed to be happening. For one, I have it set for scheduled charging at 1:00 AM, so it shouldn't have even been running yet. And two, I have it set for 31A at my house, so it runs a little bit cooler on my 1st generation UMC. What was going on was that the GPS still thought my car was several blocks away, so it was not using my home settings for amps or scheduled charging.
So about that adapter you linked to, we didn't have a lot of choice in 2013-2014 and had to do stuff like that. But it's 2020 now, and there are much better options. A company called EVSEAdapters.com makes substitute adapter pigtails for the Tesla UMC for plug types that Tesla doesn't make. They actually start from an official Tesla adapter and take it apart to put a different plug on the end of it, so it preserves the circuits inside it for temperature monitoring at the plug and for announcing the correct amp limit. They are fantastic!
So I would highly recommend to just buy the appropriate adapter from them for whichever outlet type you are trying to plug into for that dryer:
L6-20:
L6-20 Adapter for Tesla Model S/X/3 Gen 2 – EVSE Adapters
or L6-30:
L6-30 Adapter for Tesla™ Model S™/X™/3™ Gen 2 – EVSE Adapters
Curious why it caught fire if the car's monitoring voltage drop as a secondary safety measure?
If it's a case like that where it's undersized wire instead of a loose connection, I think it can get really hot before it sees very much voltage drop. Also, I remember that he has been telling that story for a very long time, and that might have happened before Tesla rolled out the software change that checked for the before/after voltage monitoring safety system.
Also, did the 2013 S max out at 80A?
Older Model S’s (if I remember correctly) had a 40 amp charger with the option to install a second charger.
Yes, until the approximately April 2016 facelift of the Model S, it had either the single 40A charger, or optionally two of them for 80A. My 2014 just has the 40A.
The car sees it's a 30amp. But it's a 3 wire, wont draw what a 4 wire will. Normal 14.50 is 4 wire dryer is 3 wire.
That is not correct. Being a 4 wire outlet instead of 3 wire has nothing to do with the amp draw capability. The three wire outlet types only have the connections for one voltage level. So they would be only 120V or only 240V. The four wire outlets have Hot1, Hot2, Neutral, and ground, so they have the extra connection points so they can be dual voltage available, so parts of the appliance can use 240V and parts of it can use 120V.