Hoping someone knows what’s going on - I have the 5-20 adapter on my mobile charger plugged into a 20A circuit at work, and until recently I was pulling 16A while charging. The last few days and at different 20A outlets, my car has only been charging at 12A despite the display showing 16A max rate. See screenshot. I’ve tried a reboot. Does anyone know why this is happening?
-
Want to remove ads? Register an account and login to see fewer ads, and become a Supporting Member to remove almost all ads.
20A circuit, Suddenly limited to 12A charging
- Thread starter SandiaView
- Start date
You've most likely got a bad connection in the outlet or circuit breaker. 105V is well below where it should be, and the car is trying to get what it can without burning down your building.
I guess its also possible the main line feeding your workplace is running at a lower than usual voltage..... manually set the current down to the minimum, or read what the voltage is before the current ramps up. In an ideal world, it would be 120V give or take a few percent. You'd also likely lose a few percent(under load) getting to the outlet.
I guess its also possible the main line feeding your workplace is running at a lower than usual voltage..... manually set the current down to the minimum, or read what the voltage is before the current ramps up. In an ideal world, it would be 120V give or take a few percent. You'd also likely lose a few percent(under load) getting to the outlet.
jdcollins5
Member
The car measures voltage drop, and if you have too high a voltage drop, it will limit the current.
Does anyone know the amount of voltage drop that is tolerable? It would be great if the Wall Connector implemented a limit that matches electrical code recommendations: if voltage sags by more than 3% when under load, then assume that this drop is on the branch circuit, and therefore exceeds recommendation NEC 210.19(A)(1)), so should be avoided.
To implement this, the Wall Connector would need more than a "low voltage cutoff": it would need to remember the voltage with no load, and then monitor the sag in voltage under load.
ElectricIAC
Good-Natured Rascal
I think there’s been some changes in L2 charging behavior lately as even my 40A setup likes to stay between 33-34A for a couple minutes right after plugging in before ramping up all the way.
The wall connector is not where this functionality is or should be. It is the car that requests certain amounts of current and detects and adjusts for what the voltage levels are doing.
ANSI C84.1 is the standard that you are looking for. Equipment should be designed to handle (and a branch circuit should deliver no less than) 108V under normal operation (unless the load is for lighting). Additionally, equipment should be able to handle further drop to 104V but that should be considered suboptimal and be a repair condition for the circuit.
davewill
Active Member
Furthermore, the car may remember that lower charge rate for that location. You may want to try manually pushing the charge rate back up and see if it sticks.
210(19)A is just a recommendation. It recommends to limit sag on the branch to 3%, and sag on the feeder to 3%, and combined sag to 5%. But if energizing the car's charger caused a 5% sag, because the car can't check if some of that sag is at the panel, it would need to assume that all the sag is on the branch (and it would probably be right).
There are other recommendations in 215.2(A)(1) IN 2&3, 310.15(A)(1) IN 1, 310.60(B) IN 2, 455.6(A) IN, but I think they are all just Informational Notes.
BTW, this is a huge safety feature; as more high-amperage appliances get "smart brains", if they could all monitor for sag, that would bring a significant increase in safety. I'm thinking of water heaters, strip heaters, etc.
EDIT: 647.4(D) is actually a hard limit (not recommendation) of 1.5v+1.5v or 2.5% combined feeder+branch for "sensitive equipment", which NEC doesn't define. But if Tesla decides that their cars are "sensitive equipment", then 2.5% or 1.5% are good answers. Note that Teslas also need to charge in Mumbai, so Tesla should think twice about deciding their equipment is "sensitive."
Last edited:
I'd call Teslas completely not-sensitive equipment for that definition. In the 240volt range, I know Stacy's Mom doesn't care if she's getting anything from 183 to 283 volts. I imagine she would be just as happy at lower voltages or slightly higher voltages.
eprosenx
Active Member
I wonder if the voltage dipped too low one time and so the car backed off to 12a (the 75% threshold). Can you try using the plus arrow on the charging screen to bring it back up to 16a again? You should have gotten a warning about why it dropped the charge rate.
Indeed 105v is fairly low, but we need to know what the starting voltage is before it ramps charging. The car takes a baseline when it starts and then compares it against current to decide if it needs to scale back to 75% or discontinue charging altogether.
I wonder if there is other stuff on that circuit now that is drawing power or if something otherwise changed that reduced the overall system voltage.
Yeah, so rectifiers like in the Tesla are built to operate over huge ranges to deal with lots of different global power systems. In servers and most personal electronics everything is pretty much 100v-240v nominal rated (which means it can even handle + or - a bit from that range to deal with system fluctuations). The Tesla chargers are even built to go higher than that in many cases (up to 277v nominal).
So yeah, they are super not sensitive in and of themselves. They become sensitive because Tesla programs the software that way in order to try and keep from burning houses down. Basically Tesla can only monitor voltage under charging load. It reads the value before starting to charge and continues to monitor it as it ramps up to max amperage and during the entire charging session. Voltage drop does mean heat is being generated somewhere, but if it is 1000 watts over a several hundred foot long set of wire (and even back to the serving utility transformer), that is not actually the end of the world. Where it becomes really bad is if that is at a single wire nut which then melts down and catches something on fire.
Note that this is also why Telsa includes temp sensors everywhere they can (inside Wall Connectors, inside the cable end of the Mobile Connector, etc...). Direct heat detection is a great way to determine if there is a dangerous condition!
At a condo were I was living at years and years ago, had voltage 95-105 volts. I called the electric company, they sent someone over, and I showed the guy the reading on the multimeter. We measured a few other outlets as well.
Later that afternoon they added a capacitor up on the utility pole across the street. The voltages went back to normal after that.
jp
Later that afternoon they added a capacitor up on the utility pole across the street. The voltages went back to normal after that.
jp
Similar threads
