Tesla Model 3 - 12 Volt Power Socket "Circuit Breaker" Auto-Reset

THE SHORT VERSION

The 12-volt Power Socket in our Tesla Model 3’s console stopped working.

It subsequently appears to have “reset” itself (after some unknown interval, up to but probably less than 20 hours), and is functioning normally.

I wish I could know if and when it would reset itself in the future.

THE TAKEAWAY (MAYBE)

If the Power Socket fails (or maybe any 12 volt circuit on a Tesla Model 3), leave it empty and check back after (perhaps) a few hours. It will hopefully have automatically reset.

But exactly how long to wait, and whether this procedure will always work, is at this point uncertain to me.

THE LONG VERSION

I discovered that the 12 volt Power Socket in our Model 3 was not supplying power.

In retrospect, I think it may have been dead for a while, but we do not currently depend upon the Power Socket on a regular basis, and I hadn’t had a reason to notice whether it was actually working. I think I’d attempted to charge a rechargeable flashlight from a 12VDC-USB power adapter some weeks ago, and determined there was something amiss with part of the charging chain: the socket, the USB power adapter, the Micro-USB cable, etc. But I got distracted from the task, and forgot about it. When I attempted to test-power a 12-volt cooler for a road trip, I discovered that the Power Socket was dead.

When I went to plug in the 12-volt cooler, I had to remove a 24 watt 12-volt dual-port USB adapter which had been in the socket (this may be important). This typical auto adapter to charge mobile devices via USB claims a maximum output current load of 4.8 amps - 2.4A per device. Tesla’s Model 3 Owner’s Manual claims that the Power Socket is capable of “up to 12A continuous draw (16A peak),” so this single device, if operating correctly, should use well under half the available current rating for the Socket. 

But the cooler didn’t start. Eventually, I tested a few other 12V-USB adapters in the Model 3’s socket, then took the entire collection of cooler and USB adapters to another 12-volt socket in another vehicle and they all functioned normally. A 12-volt accessory socket voltage tester plugged into the Model 3 Power Socket also confirmed that it appeared to be dead.

I read long ago that the Tesla Model 3 does not incorporate traditional fuses to protect its low-voltage (12 volt) circuits, but uses solid-state current control and monitoring infrastructure, which temporarily interrupts current flow when the system measures excessive current for the designed load of the circuit. These “virtual fuses” or “virtual circuit breakers” would presumably reset automatically. In searching through the Model 3 Owners Manual, I’ve thus far found no mention at all of the topic, except to mention a maximum current rating for the Power Socket (“12A continuous, 16A peak,” pg. 21 of the Dec 2018 Model 3 Owners Manual).

I tried resetting the Model 3’s user interface from the steering wheel (hold both scroll wheels until the screen goes black). No change. (The owners manual says of the socket: “Power is available whenever the touchscreen is powered on,” so it seemed as though that would cycle the power supply to that circuit, and perhaps reset the current protection mechanism.) I tried using the Controls > Safety & Security > Power Off command, waiting 3 minutes and then waking the car with brake pedal. No change. 

While all this was taking place, the Power Socket was sometimes empty, and sometimes had a USB adapter plugged in, its LED pilot light serving as a visual indicator of when the power was restored. It occurred to me that even though the USB adapter that had been plugged in for months seemed to work fine in another vehicle, that it might still have malfunctioned enough to trip the Model 3’s circuit protection system, and that even though the overcurrent condition might no longer be present, that the circuit might not “reset” until it was convinced that there was nothing connected. Even an empty USB adapter probably flows some current all the time. So I deliberately left the socket empty for several minutes, then tested it again.h I also tried two other different USB adapters.

The socket never worked that day. 

I found no useful information from online forums about how/when/if the Power Socket circuit would reset (some Tesla forum posters said that they’d experienced a reset, but gave few clues as to how much time had elapsed). One poster mentioned “36 hours,” but I couldn’t tell if that was a suggestion or experience. 

I contacted Tesla Support via their web-based chat system. I explained that we were preparing for a cross-country journey, and that we were depending upon the 12-volt socket, and asked what I could do to reset it. The chat agent responded that there was NOTHING I could do but schedule a Service appointment. I responded that we were imminently departing, and that I’d never been able to schedule a Service visit in less than several weeks. The agent responded that they had [changed their Service strategies], and that perhaps a mobile Tesla service rep would come to my location (we’re in Los Angeles, where I’d expect more Tesla Ranger visits, but so far, I’ve never even had one suggested). I said again that we were anxious that this might delay our travel plans, and the agent wrote, “I mean you can try a powercycle, but I don’t think it will help if the outlet is dead.” The chat rep pasted Power Cycle instructions into the chat window, asked if there was anything else they could help me with, and I said thank you and we ended the chat.

The provided instructions:

“Power Cycle:
1. Select the car icon on the bottom left of your screen
2. Select safety and security
3. Select power off (may be under Emergency Brake and power off)
4. Are you sure you want to power off? --> Yes
5. Wait 3 minutes
6. Open and close the door to wake the car up
7. Hold both scroll wheels on the steering wheel until you see the Tesla T logo appear.”

I tried the slightly different variation to what I’d already tried (opening and closing the door, and doing a “two thumb salute” reset afterward), but it made no difference. This was probably 30 minutes after my last testing session with the Model 3 Power Socket.

Defeated, I made an appointment with Tesla Service via the Tesla app. The scheduled appointment was 8 days away - delaying our departure by a couple of days, but I had no choice, and I hoped that perhaps a mobile service would be suggested after evaluation of my request.

HEAL THYSELF?

The next afternoon - 19-20 hours after my last test of the Power Socket - as I was about to begin the day’s errands, I tested the socket again. It worked! I wasn’t completely surprised (after all, I did test it again), and I’m happy that it’s working, but I still have NO idea whether the circuit performed an automatic reset during the night, or something else happened. And assuming that it did automatically reset, how long did that take? And were any of the other conditions (i.e., plugged into charger; Sentry Mode; devices charging from Model 3 USB ports) important?

RECAP

Here are my observations, speculations, and hypotheses about the experience so far:

• The 12-volt circuit protection system may reset itself: 1) after a certain period of time has elapsed; 2) if the overcurrent condition is no longer present; and perhaps 3) if the circuit is completely unloaded.
• Regarding item #3 above: I suspect that having the USB adapter plugged in for weeks or months may have prevented the protection system from resetting. Perhaps it waits for a period of time (1 hour? 2 hours? 6 hours?) after the overcurrent fault, and tests for presence of a load-carrying device. If it finds none, it resets. If it finds even as little load as an idle USB charging adapter, it waits to try again.
• While I’d LOVE to establish the exact amount of time one has to wait for the system to reset, I don’t currently have time to risk continuously triggering the Power Socket’s shutdown mechanism - especially if it might ultimately lead to a Tesla Service call. This would entail:
• Deliberately and repeatedly tripping the circuit protection by plugging in a device which attempts to draw more than 12A continuous/16A peak. I’d like to think the overcurrent protection system would protect the car’s systems from damage resulting from multiple overcurrent events, but that’s part of the risk of not having enough information.
• Testing a variety of periods of time to establish the threshold at which the circuit is still found to be dead. (This is tricky: trying shorter intervals first and making them longer is somewhat self-defeating, if the act of testing resets the delay period. But starting at 19 hours and progressively lowering the intervals would take days as well.)
• After writing most of this document, I discovered this Tesla Model 3 blog post from mid-2018 titled Model 3 “Fuses” where “Pete” writes:
• “The good news is that the fuses are self-resetting, which means that after the current on the circuit has settled, they'll normally reset themselves; this can take 60-90 minutes, we've yet to determine an exact time frame...”
• Why didn’t Tesla Chat Support know about this? They could have just scripted a response for the user to unplug all devices and wait overnight or a few hours, and then schedule an appointment for service if that doesn’t restore power to the circuit, rather than essentially saying “it’s broken, and there’s nothing you can do about it” which is pretty much the opposite of the actual answer.
• While it may be a positive that the Model 3 can automatically reset its 12-volt systems without any action from the user, it’s important that we users identify the difference between a system that’s “going to eventually reset itself,” and one that won’t be working for another three weeks. For 19 hours, that’s where my wife and I were: changing our travel plans and figuring out a way to manage the trip without any 12-volt accessories.
• (While this may seem trivial to those who don’t use 12-volt devices, consider that there may be Model 3 owners powering important health-related devices like oxygen concentrators and CPAP machines.)

THE CUTTING EDGE OF AUTOMOTIVE ELECTRICS, BUT...

The good part about the Tesla Model 3’s 12-volt circuit protection system is that there are no fuses. The whole system is protected by solid-state systems that function as circuit-breakers, interrupting electrical flow to a circuit which has exceeded its safe maximum current load.

Also good: that the system appears to automatically restore power to the affected circuit when the overload condition is resolved.

I just wish I could be confident that the Power Socket - or any of the Model 3’s 12 volt systems - would automatically restore themselves in the future, and I would like to know with any certainty just how long we’d have to wait for the self-reset if this reoccurs, to determine whether the symptom was the result of a protective action or a system failure.

So far, I’ve found no explanations, only read theories and speculations from unconfirmed sources. I hope that can be remedied.

I’d love to hear the Straight Scoop from Tesla about exactly how this is supposed to work, and what Model 3 owners should anticipate if they trip one of the current protection devices. I think their corporate attitude is that as far as users/owners are concerned, it’s just “automatic” and takes care of itself (like windshield washers, and headlights, and other things over which I which we could take control, or take control more easily). And despite the fact that this is NOT reflective of a Tesla product failure (indeed, the “breaker” trips because of an external device failure or because the operator attempted to connect a device with an excessive current draw), it may be that Tesla thinks this makes some sort of negative association with users - as though the car’s systems were substandard or incapable.

EXPLANATIONS ABOUT VOLTAGE AND CURRENT

Voltage is a measure of the potential for electricity to flow between two parts of a circuit. It sort of represents the readiness, if you will, of electrons to go from one place to another. Our homes have 120 volt and 240 volt devices. Traditional automobiles and the some of the Tesla’s systems, like lighting, audio entertainment and HVAC, are 12 volt. Our Tesla’s propulsion battery packs and motors operate in the 350-400 volt range.

Current, measured in Amperes or Amps, represents how much electric charge actually passes from one place to another in a circuit. Devices which use electricity will attempt to take as much current as they can without regard to whether the circuit can safely supply it - it is the responsibility of the user and the designers of the power distribution infrastructure (wires, connectors, fixtures, etc.) to appropriately select and design them for the intended loads. Components are initially selected based upon an economic balance of cost versus required performance. Put another way: wiring is only as big as it needs to be to confidently assume liability risk. 

(NOTE: Modern electric vehicle charging represents an exception to the device current demand model, as EV's on-board charging systems actually communicate with charging interfaces, which report how much current they can safely supply, and the on-board charing system within the EV then safely limits its current draw below the reported amperage available.)

Circuit breakers and fuses are intended to protect distribution infrastructure from catastrophically and dangerously failing (i.e. wires in your home’s walls from heating enough to ignite surrounding structures) by interrupting electrical flow well below the current limits of the distribution components. 

TESLA OWNERS MANUAL - 12 VOLT POWER SOCKET

From the December 20, 2018 “Model 3 Owner’s Manual” PDF file:
12V Power Socket

Your Model 3 has a power socket located in the center console's rear compartment. Power is available whenever the touchscreen is powered on.

The power socket is suitable for accessories requiring up to 12A continuous draw (16A peak).

Warning: The power socket and an accessory’s connector can become hot.

Warning: To prevent excessive interference with the vehicle’s electronics, Tesla recommends that you do not plug any non-Tesla accessories, including power inverters, into the 12V power socket. However, if you do use a non-Tesla accessory and notice any malfunctions or unexpected behavior, such as indicator lights, alert messages, or excessive heat from the accessory, unplug the accessory from the 12V power socket immediately.

⚠️Caution: Do not attempt to jump start Model 3 using the 12V power socket. Doing so can result in damage.