Tesla Universal EVSE Connected, but 12V battery drained

I don’t have the Tesla Connector or the Juicebox device that is under suspicion. What is the age of the 12V battery? One possibility is that it just decided to die at the same time the new device was put into service.

Were you able to revive the battery and power up the car? If so, voltage at the 12V could be measured while charging the HV battery to confirm that a charging voltage is reaching the 12V battery. This should be tested with and without the Tesla connector. The L2 device does not charge the 12V battery directly. It charges the HV battery and a DC/DC converter chargers the 12V from the HV battery. If charging is taking place, both batteries should be getting charged, unless the converter has failed.

My understanding of the “handshake” is that it is essentially a compatibility/safety check between the power source and the vehicle. Did you notice if the green light at the charging port was on and not blinking after the connection was made? That would indicate that the handshake was successful and charging had begun. Noises under the hood, such as fans and circulation pumps, are also indicators that charging is taking place.

I don’t know if the handshake goes on endlessly in hopes of reaching an agreement or if it’s a once and done affair. If the former is a possibility then that could certainly drain the 12V battery.

 

I was always under impression that 12v battery is not charging when evse connected. Did some measurements right now - I was wrong and right at the same time.
So the experiment:
Car is off for hours, battery level about 50%, charging scheduled for 19:00. All manipulations done by the app, to prevent lights coming on with doors openings)

18:40 - 12.961v (charging will start at 19:00 by schedule)
19:00 - 13.358v (not really a charging voltage, but something coming in)
19:07 - 13.345v (that something slowly dropping)
19:25 - 13.323v (dropped some more)
Stopped charging by the app
19:26 - 12.871v (normal battery voltage, no charging)
Started charging again, put the car ON
19:27 - 13.335v (again, some trickle charge. I would expect with the car ON I'll get a normal charge, but no)
Removed EVSE connector, car still ON
19:29 - 14.582v (so, 12v battery gets normal charging voltage only when EVSE disconnected, and car is ON. With EVSE connected it will be only trickle charge.

Next tests will be to check if I turn on climate remotely - will it send charging voltage to 12v battery or not. (need to know in case I leave the car at the airport for weeks).

 

On the graph it goes from 12.71 DOWN to 12.74 and then UP to 12.45 - typo somewhere?

 

Looking at the drop from 12.4v to 9v in a matter of minutes - I’d say your 12v battery is busted and had to be replaced. Whatever Tesla evse does to the car it should not cause such a steep drop. It would require something like a starter motor trying to start a cold engine in terms of amps.
I’d repeat a test with a ampermeter clamp on the battery.

 

You are correct that the 12V, or for that matter the HV battery, will not be charged when an EVSE is connected. Charging must be initiated for either to occur.

“Normal” charging voltage varies based of the SOC of the battery. A typical maintainer will hold a battery at 13.0-13.1V. The 13.3’s that you measured are appropriate charging voltages for a wet cell that is nearing a full charge.

What you are seeing when the system is ON, is the DC/DC converter, sending a voltage to a battery that is under load. That voltage will vary as the load changes. This can be observed by turning items, such as the headlights, dash fan or even the stereo on and off while measuring voltage.

 

This does appear to be the case. A battery coming off a charge at 13.1V will revert to a nominal resting voltage of 12.7-12.8V over time. What is most telling in the chart is the voltage recovery after disconnecting the Tesla device.

Wet cell voltage will sag under load and recover when the load is removed. That is what we are seeing. The Emporia device also shows an immediate drop in voltage, presumably from the “handshake”. It then releases its grip after detecting that no charging is necessary. The Tesla device, which is the only variable, doesn’t let go. It could possibly deplete the battery prior to charging as well, if plugged in and charging wasn’t scheduled for several hours. We all know that charging will not happen if the 12V is dead.

I’d imagine that a software update could resolve the issue, however, Tesla would need to be made aware of the situation. It would also be interesting to know if this is a Clarity specific issue.

Your 12V battery is likely in need of replacement, even though we don’t know the age of the battery. Having been depleted below 10.5V on a few occasions, it isn’t likely to last much longer, even though it appears to have recovered. I recently replaced mine after just over 4 years, with the Honda battery. It has a full 3 year warranty after which it is pro-rated for 100 months. Cost was $130.

 

Did you purchase the Tesla EVSE because you own or intend to own a Tesla and wanted a single device to charge various EV’s?

Is the Tesla Wall Connector energized by a dedicated 60A circuit so that the maximum charging rate can be achieved?

 

Measured voltage with full battery and evse connected - 12.81v, not changing over time, so battery is resting as it should be.
Removed EVSE, same voltage, not changing, car fully off.
Put EVSE back, started climate by the app - 12v battery started to receive a trickle charge of 13.36v, just like when EVSE was charging the car.

For me it means if a car left for weeks - to keep it alive it may make sense to turn on climate occationally.

 

While not generally considered a deep cycle battery, I’ve seen Group 51 batteries with reserve capacities as low as 45 minutes. That would convert to about 5 hours at 3.8A until a healthy battery would be at 10.5V. It might last a few hours longer since the load is less than the 25A standard used for determining RC.