Boondock 12 volt charging for RV battery with a Tesla.

[Reisender]

Just a heads up for those towing RV trailers with Teslas. The 12 volt charge line on the 7 pin connector deactivates shortly after the drivers seat is vacated. This means that the RV will not draw off the Tesla to charge its 12 volt battery. That’s pretty much normal operation with any tow vehicle now.

However, if one has run their RV battery down after a few days of camping an emergency go to procedure has always been to just connect the trailer to the tow vehicle and get a charge so one can run the furnace etc. This is not possible with the tesla as the 7 pin 12 volt charge line goes dormant when the driver gets out of the car.

The alternative is to use the ACC aux socket in the trunk of the model Y (and probably X, assuming it has one). Make a cable with a female 7 pin receptacle and a cigarettes' lighter plug on the other end. Hook up the two appropriate pins (see any 7 pin diagram for the right pins). You MUST leave the Tesla in sentry mode. Then the ACC aux plugs stay active.

We made a jig using a cheapy tool box to monitor the current and voltage and observed about 13.3 volts and 5 to 7 amps of current leaving the Tesla although the trailer battery wasn’t very run down at the time so it didn’t take much of a charge. It also has a cheapy renogy 9 amp DC to DC isolation converter in line which limits the amount of current drawn from the 12 volt acc plug in the Tesla as it has a 16 amp current limit.

Anyway. Hope this helps someone freezing in their trailer because the RV furnace motor won’t spin fast enough to open the sail switch and enable the furnace. Been there. In our trailer it’s an ALDE hydronic heat and hot water system but same idea. Needs 12 volts for the circulation pump etc.

Heads up. Cameras don’t play nice with LED displays so they appear to be displaying gibberish in the pictures, but in the real world are a nice indicator of what’s happening. Also first pic is a bench test pic using a booster pac as a source. Important for a geeky guy like me. ??.

Cheers.

John.





And just a gratuitous purdy campground picture from last week. 🙂

[Reisender]

Matt_Colie wrote:
This sounds like "The truly superior pilot is the one that uses his superior judgement to preclude having to demonstrate his superior piloting skills".

If the Tesla was a hybrid, you might have a better chance. Or, you might be able to build a switching power supply to pull power from the main traction battery that I believe is 450V and about 40kWhr.

One of the great stories to me was that the Tesla Cars do have a 12v

battery that is there to power conventional systems, and if it goes down the vehicle is disabled.

Matt

Good morning Matt.

Typical Tesla car Battery is between 72 and 100 kWh batteries.

Amost all EV,s have a small 12 volt batteries for compatibility with common automotive components. Lights, fans etc.

Cheers.

[Matt_Colie]

This sounds like "The truly superior pilot is the one that uses his superior judgement to preclude having to demonstrate his superior piloting skills".

If the Tesla was a hybrid, you might have a better chance. Or, you might be able to build a switching power supply to pull power from the main traction battery that I believe is 450V and about 40kWhr.

One of the great stories to me was that the Tesla Cars do have a 12v battery that is there to power conventional systems, and if it goes down the vehicle is disabled.

Matt

[Reisender]

JKJavelin wrote:
I'm pretty ignorant about EVs,but I would think that the number 1 concern would be draining the vehicle's battery, doing everything possible to conserve it. Why jeopardize it for the rv?
JK

Good morning JK. I can see where you are coming from. But the numbers are pretty safe. Typically an EV SUV like this will have an 80 to 100 KWh battery and charging a battery over a day mighty be a couple kilowatts. Maybe if you did it for a month or so. Even then one could just drive the SUV to a Supercharger, “tank up” for 15 or 20 minutes and start over again.

Hope that helps.

Safe travels.

[Reisender]

valhalla360 wrote:

jdc1 wrote:
It was just announced Tesla will not honor the warranty if you use it to power your house.

Sure, they just won't honor warranty for the modifications you need to do to actually make it power the house.

It is interesting though. I’m not sure how someone would do that with a Tesla. I mean the only access is the 12 volt accessory ports that peak out at 16 amps at 12 volts. Good enough for a laptop or cooler or small battery charger but really no way to hook it to a house. I wonder if some people are finding a way to tap into the main 400 volt traction battery. Interesting.

[valhalla360]

JKJavelin wrote:
I'm pretty ignorant about EVs,but I would think that the number 1 concern would be draining the vehicle's battery, doing everything possible to conserve it. Why jeopardize it for the rv?
JK

Obviously, if you are using the full capability for propulsion, you wouldn't want to draw off the battery.

But say you are a contractor with an F150. You are working 20 miles from your home base, so you need 40miles of range and you can plug it in at the yard for the night. If you have a 200mile range, you have 160miles of range that you could repurpose for other power needs.

Operating a circular saw or a compressor for a nail gun off the battery bank is quite viable and avoids the need for a separate generator. The electric F150s can come from the factory with an AC inverter built in, so you just plug in your tools and start working.

The Tesla option is more of a curiosity as it is only putting out a few amps at 12v. Not enough to run anything substantial but you can keep the RV battery up if boondocking with minimal power consumption. 10amps @ 12v is around 0.12KW. You could pull that for 24hours and only use a little less than 3KWH...out of something like an 80-90KWH battery bank, so unless you are using absolutely all your range to get to the camp site, you can generally get away with topping up the battery.

[valhalla360]

jdc1 wrote:
It was just announced Tesla will not honor the warranty if you use it to power your house.

Sure, they just won't honor warranty for the modifications you need to do to actually make it power the house.

[JKJavelin]

I'm pretty ignorant about EVs,but I would think that the number 1 concern would be draining the vehicle's battery, doing everything possible to conserve it. Why jeopardize it for the rv?
JK

[Reisender]

jdc1 wrote:
It was just announced Tesla will not honor the warranty if you use it to power your house.

Yah I can see that. I wouldn’t even know how to do that. :).

[jdc1]

It was just announced Tesla will not honor the warranty if you use it to power your house.

[Reisender]

Matt_Colie wrote:
Honest question.
I kind of hate to sound like a Luddite here, but wouldn't be cleaner, safer and easier to just carry a little gas powered generator?
You would only need to run it when things got bad.
Matt

Yah. It’s a great idea and we actually do that. We picked up a little champion propane 2 KW inverter generator. Super quiet. Works well for battery charging. Not sure if it would work for the AC but really didn’t buy it for that.

Keep in mind Matt that I’m a retired geeky ex Air Force technician guy who likes to build stuff...just because. :). In my little mind I envision using my home brew hack if the trailer battery runs down during the night and I need enough power to get the heating system going. In the eyes of my wife I’ll be a hero and that’s all that matters. :). Next morning can run the generator for a couple hours and charge up the AGM’s.

Cheers. :).

[Matt_Colie]

Honest question.
I kind of hate to sound like a Luddite here, but wouldn't be cleaner, safer and easier to just carry a little gas powered generator?
You would only need to run it when things got bad.
Matt

[Reisender]

LittleBill wrote:
throw a rock on the seat... seems complex for what could be a 2 second fix.

My guess is it takes more than a rock but we’ll experiment with it next time out. There is the issue of security though. The car would have to be “enabled” which means it could be driven away. That might be a problem. Hmmm

[LittleBill]

throw a rock on the seat... seems complex for what could be a 2 second fix.

[Reisender]

valhalla360 wrote:

time2roll wrote:

valhalla360 wrote:
Probably far fewer Tesla owners are likely to benefit on a regular basis from a similar system.

Easy software update if there is a calling.

The Ford system outputs 120v AC power. I believe around 3000w peak.

To my knowledge, the Tesla can't do that with a software change. The current 7pin output being discussed is something like 7-10amps 12v DC. OK for keeping the battery up for small loads but doesn't really take advantage of the large battery bank that's available (assuming you aren't saving it for propulsion).

Doesn't mean they couldn't add an inverter at some point (physical not programing) but as mentioned, Tesla users who would significantly benefit are likely a far more rare buyer.

Yah, it’s 12 amps constant and 16 amps peak. It’s on a software fuse. Resets after 10 minutes is you exceed the rating.