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]

valhalla360 wrote:

Reisender wrote:

LOL. :). I never thought of the 50 pound weight thing. Next time we are camping maybe we’ll try that just for kicks.

Sorry, I've done the same thing...worked thru a detailed solution only to have someone bypass the whole issue.

Who knows, maybe they have a heartbeat monitor in the seat or something else making it so a weight won't work.

I haven't heard much about it lately but Ford really took a smart lead on this with their electric F150 models. With big battery banks when you don't need all of it for propulsion, it's a great alternative to a generator. I suspect with Tesla it simply doesn't line up with their core business model. Lots of contractors and campers can benefit from their F150 replacing a generator. Probably far fewer Tesla owners are likely to benefit on a regular basis from a similar system.

Yah I totally agree. They did show a 120 and 240 volt plug on the Cybertruck intro a couple years ago. My guess is it will make it into production. But who knows.

I like that F150 lightning. Think it will be a nice truck. Unfortunately a truck is not in our immediate future. Right now we are a one car family and it can’t be a truck for a number of reasons. But the model Y is serving us well as our tow vehicle and general purpose wheels. We are not ruling out a truck in a few years and even have a reservation for a Cybertruck (just in case :).

Anyway. Lots of new tech coming down the pipe.

[valhalla360]

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.

[time2roll]

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.

[valhalla360]

Reisender wrote:

LOL. :). I never thought of the 50 pound weight thing. Next time we are camping maybe we’ll try that just for kicks.

Sorry, I've done the same thing...worked thru a detailed solution only to have someone bypass the whole issue.

Who knows, maybe they have a heartbeat monitor in the seat or something else making it so a weight won't work.

I haven't heard much about it lately but Ford really took a smart lead on this with their electric F150 models. With big battery banks when you don't need all of it for propulsion, it's a great alternative to a generator. I suspect with Tesla it simply doesn't line up with their core business model. Lots of contractors and campers can benefit from their F150 replacing a generator. Probably far fewer Tesla owners are likely to benefit on a regular basis from a similar system.

[Reisender]

valhalla360 wrote:
Can you just put a 50lb tool box (or other heavy item ) in the drivers seat to keep the 7pin going?

Tangentially related: I was thinking about if you have a toy hauler with a 48v golf cart. 8- 200 amp-hr @ 6v batteries hold around 10kwh...or about 5kwh usable power. Compared to your typical RV battery bank (even a lot of boondocker battery banks), that's pretty massive. If you do find your RV battery bank low and you aren't planning to depart, it could be a good source of power to get thru an extra few days.

A 48v DC to 12v DC converter should be fairly simple to wire up and would give you a backup battery source.

LOL. :). I never thought of the 50 pound weight thing. Next time we are camping maybe we’ll try that just for kicks.

Golf cart thing would be a pretty big reserve for an RV if you had one handy. Can’t see why that wouldn’t work either. That’s thinking outside the box.

Cheers.

John.

[valhalla360]

Can you just put a 50lb tool box (or other heavy item ) in the drivers seat to keep the 7pin going?

Tangentially related: I was thinking about if you have a toy hauler with a 48v golf cart. 8- 200 amp-hr @ 6v batteries hold around 10kwh...or about 5kwh usable power. Compared to your typical RV battery bank (even a lot of boondocker battery banks), that's pretty massive. If you do find your RV battery bank low and you aren't planning to depart, it could be a good source of power to get thru an extra few days.

A 48v DC to 12v DC converter should be fairly simple to wire up and would give you a backup battery source.

[Reisender]

time2roll wrote:
No jump direct off the Tesla 12v accessory battery? Not sure about access but I understand 1000 watts can be pulled off this battery as long as the vehicle is on.

Maybe. We haven’t tried it. But I have read that the software detects the “leakage” and throws a code. We could do that in our leaf though with no problem.

Keep in mind that I’m a gadgety geeky dude with nothing better to do than make stuff that “may be” handy some day. In the cold we were good for three days with a little filtered sunlight. I suspect once it gets warmer we’ll be fine for 4 or 5. By then our water is getting low, our black and grey are getting full and it’s time to move on anyway. The tesla does charge the trailer battery when it’s going down the road.

It’s all fun. :).

Cheers.

John

[time2roll]

No jump direct off the Tesla 12v accessory battery? Not sure about access but I understand 1000 watts can be pulled off this battery as long as the vehicle is on.

[Reisender]

theoldwizard1 wrote:

Reisender wrote:
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.
.
.
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Love the plastic tool box complete with meters !

The smallest Renogy DC-DC charger I can find is rated at 20A. Got a model # ?

My mistake. Its a victon. I get those two mixed up. Duh. The solar controller is Victron as well.

[Reisender]

Lwiddis wrote:
Interesting work around. TY for posting. Have you considered solar on the TT?

Yah its hard to see in the pictures but the trailer comes stock with a 165 watt panel and Victron controller as well as 2 X 6 AGM batteries mounted under the bed.

You can kind of see it in this pic. Its above the window.

[theoldwizard1]

Reisender wrote:
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.
.
.
.

Love the plastic tool box complete with meters !

The smallest Renogy DC-DC charger I can find is rated at 20A. Got a model # ?

[Lwiddis]

Interesting work around. TY for posting. Have you considered solar on the TT?