Just chiming in with everybody else. Current draw is set by:
- Car finds out how much the connector to AC/DC (L1, L2/ Supercharger) can supply.
- Car figures out how much it can accept. (More or less, looks at its navel.)
- Picks the lower of #'s 1 and 2.
- If, while charging, Stuff Happens, it may reduce the current. What little I know under this category includes:
- Drop in AC voltage. Happens when a Mobile Connector is being used with an extension cord (personal experience). The high current on an extension cord whose advertising (Heavy Duty!) may have gotten past its actual current capacity results in an I-R drop across the suspect cord. The cord, if left in this state, would heat up to the point of letting the smoke out, so Tesla's programmers reduce the current draw. Since they don't like smoke, either. Similar can happen with loose connections to the breaker panel/in the wall/in the socket (worn contacts, anybody?), and so on. And probably includes loose connections inside the car, although I haven't heard of somebody suffering through that one, yet.
- High temperature on the Mobile Connector plug that goes into the wall. Oddly enough, the Mobile Connector reports its temperature back to the Mothership (the car) and, if the temp starts getting Up There, the car will cut back or simply stop charging. This can be because of cheapie or mis-installed sockets reaching End of Life or even a bad temperature sensor.
- Battery getting full. This is Extremely Obvious during supercharging, when one's initial 120kW/150kW/240kW rate slows down once one gets past 30% state of charge or so. But if one is going for 100% charge on a L1/L2 charger, the charge rate also slows down when one gets higher than 90% or so. The last 1% take XXX more than the first 1%, and all that.
The odd part about
@BLH17's post is that the car isn't throwing error messages left, right, and center. In my experience, the car's not shy about putting up error messages for items #1 and #2 above; not so much for #3, since that's not an error, that's expected behavior. Trying somebody else's Wall Connector might be in order. Looking for Destination Chargers (which are typically Tesla Wall Connectors (TWC)) and using one might be in order. Similarly, Tesla Service Centers have the things in the parking lot and, of course, if one is at a Tesla SC, they'll typically let one do a little self-checking.
Finally: If it turns out that everything is sweetness and light with your car at somebody else's TWC or whatever, then it might be a good idea calling Tesla's support line for the TWC. Back in the day, one of my co-workers got a Gen 2 TWC for his snazzy new Tesla. He was having an electrician do the wiring. Said electrician didn't read or pay attention to the entry in the manual for the TWC and therefore didn't follow the instructions that stated, "Do not adjust the switches on the TWC with the panel breaker on." Which resulted in the discovery, after the electrician left, that the TWC was toast.
My co-worker called the Tesla hot line in the manual and got a live body on the third ring (cue me falling over in astonishment). Who did a bit of troubleshooting and then drop-shipped a new TWC to our guy, without our guy having to pay.
Not sure if you'll get that kind of service these days, but one never knows. And I think the Gen 3 TWCs have internet connectivity; not sure, but there might be some logs in there.