Does Mobile connector automatically set amps?

[LJCard]

I plugged my mobile charger with its NEMA 5-15 adapter into an outlet at work and the outlet GFCI kept tripping. I tried a bunch of times before I realized in the app that it was trying to charge at 40A. I was under the impression that the mobile charger would automatically detect and set the charge amps. Will I need to manually select and number of amps every time I charge at a new place?

 

[jrweiss98020]

The adapter should automatically set the max amps. Maybe there was already a load on the circuit, and it couldn't take another 12 amps. OR the breaker is faulty, and can't take 12 amps...

 

[RayK]

The Tesla mobile connector should automatically set the charging amps, based upon the NEMA adapter that is plugged into it. If you are not getting what you think is the proper current limit (and 40A is definitely not what a 5-15 allows), there can be a couple of things that could throw it off:

• NEMA adapter is not fully plugged into the mobile connector.
• The NEMA adapter is defective (there's a chip/resistor inside that "tells" the mobile connector what it is).
• The mobile connector is defective (it cannot "read" what type of NEMA adapter is connected).
• The car previously charged at a 40A outlet at your work (i.e., a 14-50) and remembered that fact. The car should have adjusted when you used your 5-15 adapter but maybe one of the previously mentioned points hindered that adjustment.
• It would not be recommended to continue to manually set the charging current in the app or car until you can determine what causes this error.

And finally, are you sure that the 40A limit was in effect while the car was being actively charged? The app will default to a maximum limit if not charging. My app currently shows a 48A limit that can be adjusted downward but the only time I've ever charged at home was with a 5-15 outlet and that was years ago. (The car is in my driveway and not charging)

Note: the mobile connector is supposed to have it's own built-in GFCI. That can interfere with a GFCI breaker and cause it to falsely trip. About the only thing you can do is replace the GFCI breaker with one that isn't as sensitive. You should not use a non-GFCI breaker unless your electrical code allows (most will not if the outlet is in the garage from what I know).

 

[davewill]

At it's highest, the mobile connector can only charge at 32a regardless of what adapter is plugged into it. I suspect you are somehow misreading what the phone app is telling you. The outlet GFCI is likely tripping because of the ground current check the mobile connector does before energizing the plug. This happens when the GFCI is too sensitive, either because it is old (modern ones are less sensitive), or because it is failing. The only way to fix it that I know of is a new GFCI.

 

[RayK]

@LJCard Yes, @davewill is correct. The Tesla mobile connector tops out at a maximum of 32A, regardless if you're connected to a 50A outlet. I had a brain fart there, sorry. Given that you've quoted a 40A "limit", I'm going to have to go with a misread / misunderstanding.

Also, re-reading your OP, I now understand that the GFCI is in the outlet and not the breaker back at the electrical panel. My supposition still applies; the circuit test that the mobile connector does is triggering the outlet's GFCI. Do you know if there are other outlets on the same circuit and if they were being used at the time you were charging?

 

[LJCard]

Thank you @davewill and @RayK for your responses!! I plugged into the wall and the "Tesla" lit up appropriately. I plugged the other end into the car and the T turned blue, then I heard the click on the outlet of the GFCI tripping, then the "Tesla" on the cord went dark. The only thing that stopped this from happening, was going to the app and manually changing a box that said "40A" and changing it to "12A". When I did that and plugged in, everything worked and the car charged properly the entire time. I had tried several different outlets/locations in the same garage. I guess I should ask my service team to take a look at my mobile connector and NEMA adapter? it really seems like it had no idea which adapter was plugged in.

 

[davewill]

You didn't mention that you were able to get it to charge. When it's charging, the screen in the car should display the amperage as a pair of numbers separated by a "/". The first is the number of amps you're currently drawing, and the second is the max number of amps the car thinks the current plug can supply. What does your car say while it's charging? It might also be helpful to know what the voltage display says.

 

[RayK]

A bit strange, from what I understand about mobile connector charging (I'll admit, not everything since I don't charge at home). My suggestion would be to first re-seat the 5-15 NEMA adapter from the mobile connector (pull it out and plug it back in firmly). Then try charging at a different location from work and see what current the car thinks it should draw (from the main screen as outlined above: an xx/xx A).

Or, you could leave your NEMA adapter/mobile connector combination alone and take it to Service and see what they say about it. As I mentioned earlier it could be a defective adapter, defective mobile connector or a loose connection. That you got a successful charge out of it after manually turning down the current doesn't lead me to believe any ones of those explanations above the others.

 

[smatthew]

Thank you @davewill and @RayK for your responses!! I plugged into the wall and the "Tesla" lit up appropriately. I plugged the other end into the car and the T turned blue, then I heard the click on the outlet of the GFCI tripping, then the "Tesla" on the cord went dark. The only thing that stopped this from happening, was going to the app and manually changing a box that said "40A" and changing it to "12A". When I did that and plugged in, everything worked and the car charged properly the entire time. I had tried several different outlets/locations in the same garage. I guess I should ask my service team to take a look at my mobile connector and NEMA adapter? it really seems like it had no idea which adapter was plugged in.

This is interesting because GFCIs are not overcurrent devices. A GFCI measure the differences in current flow, not totals. GFCI current breakers not withstanding.

 

[ChrisLA]

In addition to automatically setting up the max current limit of the Mobile Charger depending on the NEMA adapter currently connected to the charger, the car will automatically further reduce the current the car draws to prevent the wiring from overheating. The car has no direct way of measuring the wiring's temperature along the entirety of the wiring's path --in fact, it has no way of measuring it anywhere outside the Tesla engineering umbrella -- but it can estimate it based on the voltage the car measures. As the wiring heats up, its resistance increases and the voltage drops. By continually monitoring the voltage, the car uses voltage as a proxy for temperature and adjusts the current draw to keep the voltage --and therefore the wiring's temperature -- in an acceptable range.

I observed this behavior yesterday. My home charger died and for the first time had to charge the vehicle by connecting the Mobile Charger to a 12A receptacle in my garage, through an extension cord. I was concerned about fire hazard and monitored the first few hours of charge closely. The charger recognized the pigtail and set the correct 12A limit. But within an hour the car had dropped its draw to 9A. Eventually, I felt confident enough to let the vehicle charge overnight. This morning, I observed that the car had further dropped its draw to... 7A. Better slow than toasted.

 

[davewill]

In addition to automatically setting up the max current limit of the Mobile Charger depending on the NEMA adapter currently connected to the charger, the car will automatically further reduce the current the car draws to prevent the wiring from overheating. The car has no direct way of measuring the wiring's temperature along the entirety of the wiring's path --in fact, it has no way of measuring it anywhere outside the Tesla engineering umbrella -- but it can estimate it based on the voltage the car measures. As the wiring heats up, its resistance increases and the voltage drops. By continually monitoring the voltage, the car uses voltage as a proxy for temperature and adjusts the current draw to keep the voltage --and therefore the wiring's temperature -- in an acceptable range.

I observed this behavior yesterday. My home charger died and for the first time had to charge the vehicle by connecting the Mobile Charger to a 12A receptacle in my garage, through an extension cord. I was concerned about fire hazard and monitored the first few hours of charge closely. The charger recognized the pigtail and set the correct 12A limit. But within an hour the car had dropped its draw to 9A. Eventually, I felt confident enough to let the vehicle charge overnight. This morning, I observed that the car had further dropped its draw to... 7A. Better slow than toasted.

One should understand that this feature should not in any way be relied upon. In general, if your wiring is causing the car to do this, the correct response is to immediately stop using that circuit for charging, and either fix whatever problem exists, or install a proper dedicated circuit for charging the car. In your case, I would NOT have continued to charge, even at the lower amperage, using that outlet and extension cord setup.