7 pin adapter back to tow hitch - Is there auxiliary power for new lithium low voltage battery?

[dcollet1]

I just accepted delivery of Model Y in the beginning of June with the express purpose of towing my Safari Alto F2114 camper. I ordered it with the towing package. It is replacing a 2019 Subaru Ascent. I have seen some discussion that the Auxiliary power back to the camper was disabled when Tesla introduced the Lithium low voltage battery to replace the lead acid battery. No one I have spoken with at Tesla has heard of this. The article was written in early 2022. Does anyone know if the auxiliary power pin on the 7-pin socket is now enabled? Is it a software update, or is there a hardware upgrade required?
Better yet - If someone out there is towing with a model Y and is using a brake controller and sending power back to a camper, please respond and let me know how you did it.

 

[PhysicsGuy]

I just accepted delivery of Model Y in the beginning of June with the express purpose of towing my Safari Alto F2114 camper. I ordered it with the towing package. It is replacing a 2019 Subaru Ascent. I have seen some discussion that the Auxiliary power back to the camper was disabled when Tesla introduced the Lithium low voltage battery to replace the lead acid battery. No one I have spoken with at Tesla has heard of this. The article was written in early 2022. Does anyone know if the auxiliary power pin on the 7-pin socket is now enabled? Is it a software update, or is there a hardware upgrade required?
Better yet - If someone out there is towing with a model Y and is using a brake controller and sending power back to a camper, please respond and let me know how you did it.

Great questions. I will be following this too. (I just got a Model Y.) I don't know the answers to any of your questions, but I can provide a bit of background info which I hope is helpful.
The Li battery is very small. About 99 Watt-hours. (So on its own it can barely sustain 5 amp draw for one hour.) It is also about 16 volts (not 12.6 or 14 V). On the other hand, when the car is "on", the d.c.-d.c. converter is powerful. It can in principle provide plenty of power to your Alto.
a) Would your Alto be happy with 16 volts? I am guessing that could be an issue, but I don't know for sure.
b) What size wire does Tesla provide for the V+? I have no idea, but I doubt it is big enough.

So probably there are issues that need to be addressed, but with money and expertise and maybe a dc-dc down converter?, you could have as much dc power as you want. Enough to power a d.c. fridge and charge your trailer batteries and anything else.

PS. As I recall, people who want to use a lot of dc power in the trailer while they drive (e.g., to operate a dc-powered fridge like a Dometic 3-way) use a pretty large wire for V+, like maybe #8 or #10.

 

[PhysicsGuy]

PPS. Some people who know a lot are n2mb_racing and stopcrazypp

 

[dcollet1]

Great questions. I will be following this too. (I just got a Model Y.) I don't know the answers to any of your questions, but I can provide a bit of background info which I hope is helpful.
The Li battery is very small. About 99 Watt-hours. (So on its own it can barely sustain 5 amp draw for one hour.) It is also about 16 volts (not 12.6 or 14 V). On the other hand, when the car is "on", the d.c.-d.c. converter is powerful. It can in principle provide plenty of power to your Alto.
a) Would your Alto be happy with 16 volts? I am guessing that could be an issue, but I don't know for sure.
b) What size wire does Tesla provide for the V+? I have no idea, but I doubt it is big enough.

So probably there are issues that need to be addressed, but with money and expertise and maybe a dc-dc down converter?, you could have as much dc power as you want. Enough to power a d.c. fridge and charge your trailer batteries and anything else.

PS. As I recall, people who want to use a lot of dc power in the trailer while they drive (e.g., to operate a dc-powered fridge like a Dometic 3-way) use a pretty large wire for V+, like maybe #8 or #10.

PhysicsGuy - Thanks for your input. I will check the voltages on each pin tomorrow morning and post the results here. I guess one of the things that I would like to understand is if there is any conversion of DC to DC provided by Tesla. It would seem reasonable to me that they (Tesla) would not push 16v to the the light circuit for breaking or signalling. I am not sure what the gauge is of the wire to the connector on the Tow hitch.

 

[PhysicsGuy]

PhysicsGuy - Thanks for your input. I will check the voltages on each pin tomorrow morning and post the results here. I guess one of the things that I would like to understand is if there is any conversion of DC to DC provided by Tesla. It would seem reasonable to me that they (Tesla) would not push 16v to the the light circuit for breaking or signalling. I am not sure what the gauge is of the wire to the connector on the Tow hitch.

Measuring the voltages sounds great! I wonder if the V+ slot is wired at all.

 

[PhysicsGuy]

I believe that people somewhat routinely use some 8 mm studs under the rear seat, which are connected to a dc-dc converter. 20 amps pretty doable with 6 AWG wiring; some draw higher currents. They use that to charge and power stuff, usually via an inverter. So one way to get power to your travel trailer could be from there. Connect to that and blend that into your 7-pin connector with wire of appropriate size (8 AWG might be okay for modest current). (BTW, I believe, though I am not sure, that the model Y is "chassis ground", but maybe you still need a decent size ground wire...?) A lot of potential. No real answers.

 

[MuscleCar]

I'm interested in this as well, from the perspective of using it as a small home backup system.

Problem is, as we have found out by that one guy in Texas? that killed his battery, that it still needs to go through the battery's BMS or whatever so that it correctly keeps topping it off.

Wondering if these "under seat" studs would work like this? Or if I'm better off replacing the wiring and plug from the 12v cigarette lighter to handle more current (just need 15 amps really, 20 would be icing on the cake)

 

[suzmac]

I just want to get power to my bike rack to allow the lift assist to work. Any progress on this aux power issue?

 

[IsleDriver]

When I tried to get this fixed, in about June 2023, I was told there is no fix. Tesla Y do not/will not have Aux power on the tow hitch. Related: Note that my Y, which was made in Fremont and I received early February 2023, didn’t have the internal cable connected to allow even the tow LIGHTS to work. But that was easily solved.

 

[SharonMY]

Did you find a supported brake controller for your Model Y? I’m still searching for a safe solution.

I have a 22 MYLR w factory towing. Tesla's low voltage system sends 15.5 v to the brake controller wires. Prodigy-Tekonsha told me their operating range doesn’t support 15.5. Tesla disconnected the Aux power to the 7 pin. Which ruled out the RF solution I have.

RedArc has a 24v controller that can handle the 15.5 v. but there was an issue with Tesla and RedArc wiring working out of the box,

I worked with the Rocklin CA GM and team for two years trying to get a supported solution. Was told ‘Corp didn’t expect people to tow.’ Still working on it.

I have a Nucamp TAB 320S Boondock, perfect rig if I can find a supported brake controller. In the meantime , it’s bricked.

 

[IsleDriver]

Did you find a supported brake controller for your Model Y? I’m still searching for a safe solution.

I have a 22 MYLR w factory towing. Tesla's low voltage system sends 15.5 v to the brake controller wires. Prodigy-Tekonsha told me their operating range doesn’t support 15.5. Tesla disconnected the Aux power to the 7 pin. Which ruled out the RF solution I have.

RedArc has a 24v controller that can handle the 15.5 v. but there was an issue with Tesla and RedArc wiring working out of the box,

I worked with the Rocklin CA GM and team for two years trying to get a supported solution. Was told ‘Corp didn’t expect people to tow.’ Still working on it.

I have a Nucamp TAB 320S Boondock, perfect rig if I can find a supported brake controller. In the meantime , it’s bricked.

We spent a week renting a Nucamp Boondock tear drop trailer, and drove it many miles without a brake controller. Its only 1000 lbs, so it worked perfectly well just using the car's brakes. We never felt out of control. Range decreased by 25% vs. what we would get without the trailer. We'd expected a 50% reduction, so only 25% reduction was a pleasant surprise. As we have never wanted to pull a bigger/heavier trailer (it would ruin the range), we have never investigated a brake controller. That said, the one challenge is that the on-board battery doesn't get recharged from the car. Thus, if we were to do this more often we'd need to plan for some powered camping spots (about ever 4th day), to recharge the teardrop's battery.