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How Does Charger Know Circuit Limitations?

My brother's Volt has a manual switch for use on a 110 volt circuit: 15 amps for a dedicated circuit, 8 amps for a shared circuit. I don't see any kind of setting on the Model S to limit the current while charging. I understand that the charger could sense what type of adapter is in use, and regulate the current for higher voltage circuits, but I don't see how it could know what kind of fuse or breaker is in use, or whether that circuit is dedicated or shared. I don't want to blow a fuse while charging from a motel's standard outlet.

Any ideas?

There is a setting on the screen where you can set the amperage in 1A increments. Dial it too high and you pop the circuit breaker / blow a fuse in the charging station / house. When that happens, pick a lower setting, reset and try again.

Hmm. I'll go out and check the screen again. I didn't see that setting. Can you tell me where it is?

NOTE: I have not received delivery yet. However based on playing with the showroom model and RTFM here: https://www.teslamotors.com/sites/default/files/blog_attachments/ms_owne...

When you pop the charging door, the big charging screen shows up. That is where you can:
- See current status
- Set standard vs. long range
- Adjust the charging current

The outlet will determine what the max amps are. Ex 14-50 is max 40 amp flow. The car does sense which adapter you have connected and will adjust the max pull off that. If I recall, it will pull up to 80% of the rated amps for that outlet.

I can't find the reference, but I want to say the car communicates with the charger to negotiate how charging will proceed.

My AV J1772 charger is rated at a maximum of 30 amps. The first time I plugged it in using that charger, the car automatically set it's maximum rate to 30. I'm assuming the charger negotiates with the car in this instance. I suppose the Tesla charging cord performs the same function, sensing which adapter plug is attached at the other end. I suppose that if you were to make your own NEMA 14-50 to NEMA 10-30 adapter, the cord might sense the NEMA 14-50, and initially set the max rate to 50 instead of 30. Fortunately Tesla lets you set your rate manually if needed.

Yes, I finally found the setting on the "Charging" tab. I don't know why I missed it before. I'm guessing that the J1772 unit communicates with the car to negotiate the correct amperage, whereas when using a standard outlet, the default amperage is based on the type of adapter that is connected.

This came up because I will be visiting my brother, who does his own wiring (in a Rube Goldberg sort of way). He was telling me he had his welder hooked up via a NEMA 14-50 outlet, but that he had fused the outlet at 30 amps. I don't want to blow his circuits.

A quick follow-up question on @DouglasR scenario. So if he manually sets the amp intake of his car to 30 amps *before* he inserts the charging cable to the charge port, then the car charger will *not* sense the NEMA 14-50 adapter that is being used and thus will not try to re-sets the amperage back to 50 amps? And this feature is location-based? It remembers the max amp setting for this particular location?

I've noticed several nice aspects of charging at limited amperage. I have a home-made 10-30 plug to 6-50 socket adapter (from a 10-30 dryer cord and a 6-50 socket) and this clearly requires special care and reduced amps.

(1) when the car begins charging it ramps up the current slowly; you have maybe 15-30 seconds before it draw full amps. So right after you plug in and the charging screen shows up (with its amp limiter control) you have time to set a lower limit. 24A in my case (80% of the 10-30's 30A breaker).

(2) the car geo references each place you charge and remembers current limits you set for that location. So next time I'm at my buddy's show with his 10-30 I will certainly double check everything but it should automatically limit to 24A again.

Tesla has done a great job implementing charging IMO.

@pilotSteve - thanks! Your scenario is very similar to mine. I have a custom made L14-20 plug to 14-50 socket. The Tesla supplied L14-50 adapter will get plugged into this custom made socket. Based on your description of step (1), it sounds like the amperage can only be adjusted *after* you begin charging? There is no way to adjust before charging begin? 15 seconds (probably less for me since the outlet is 20 amps) should be enough time for me to tune down the amperage? I just don't want to cause the breaker to trip or burn.

Yes, the geo feature is definitely nice so that I don't need to stress myself out every time I need to do this.


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