Charging Travel Trailer Battery from Tesla

[BerTX]

So where are the people who always say "Why are you so cheap? If you can afford a $150K car, you can pay for an RV campground"? I know they are around here somewhere...

 

[ohmman]

Those folks who traveled across Canada in their X and a trailer did the opposite. Figured out a way to charge their X from the batteries in their trailer. They might have some suggestions. fortytwo is their name in these forums.

Yes, I've touched base with them on other issues as well. The usage is reversed (as well as the implementation). They were traveling in Supercharger-bereft lands. The car needed a charge more than the trailer. I'm picturing a situation where I have excess capacity in the vehicle, and not enough in the trailer. There are plenty of places in California that would qualify.

So where are the people who always say "Why are you so cheap? If you can afford a $150K car, you can pay for an RV campground"? I know they are around here somewhere...

Heh. Yeah, I just don't like RV campgrounds in general. I want to be camping, not parking in a parking lot. Plus, many national parks and all of our local beach campgrounds don't have hookups. I'll still pay $50/night but I don't get hookups, so I'll need something to stretch the couple of days we'll be there.

 

[BrokerDon]

We have a 2011 Winnebago View (Mercedes Sprinter 3500 HD chassis with 3.0 liter V-6 Bluetec turbodiesel) which we "boondock" camp "off the grid" for days. It came with a 3.2kW Onan QuietDiesel generator but its noisy and not clean burning like the Mercedes Bluetec so I did a bunch of online research and now run our diesel generator only in emergencies. The upgrades which enabled this were:

• SunPower 327W solar panel
• Renogy 40A MPPT charge controller
• replaced all coach halogen light bulbs for inexpensive LEDs from eBay
• replaced the dual NAPA 12V "deep cycle" batteries with higher capacity 232Ah Energizer GC2 Premium 6V "golf cart" batteries (installed in series = 12V) from Sam's Club
• Wave 6 catalytic heater (doesn't use any electricity since it's radiant = no fan like the F.A.U. LP heater that came with our RV
• Jensen 12V 32" 1080p HDTV (replaced 26" Jensen 120V 720p SDTV which required the energy gobbling DC -> AC inverter to run
• dual Fan-Tastic 7350 thermostatically controlled 12V 13-speed auto rain sensing/closing ceiling vent fans to keep the RV cool in the summer while its in the sun during solar energy generation
• 12V USB and laptop chargers (NO DC -> AC inverters powering our DC electronics: MacBook Air & Pro laptops, iPhones, iPads, Garmin mountain bike GPS, etc.
• Carefree awnings over large windows to prevent solar gain

The biggest energy user is our built-in refrigerator / freezer... but it runs off the huge LP tank that came with our RV (or 30A 120V AC power when our RV is plugged in while its in our driveway we load it up for trips).

The SunPower 327W solar panel recharges our batteries to 100% even in winter... and runs BOTH Fan-Tastic ceiling fans + recharges all our electronics each day. We cook on our LP gas range or portable BBQ. The ONLY time we turn our generator is to run the 15,000 BTU rooftop AC unit or run the microwave. which is rarely (only 26 hours of generator runtime in 5 years).

Best advice is START by minimizing your power requirements FIRST including getting everything to run off 12V... Then install the correct size deep cycle batteries, and add an "off grid" solar system to recharge your batteries during the day. Yes I know there are locations where you'll be in the shade or its raining for a couple of days but for the rest of the time enjoy the endless supply of QUIET free energy from the sun.

 

[Fresh Start Detail]

I know you probably already know this, but it's helpful to keep one of these cheap testers in your tow rig to test your charging pin occasionally. My charging pin blew its fuse but I never knew it until it was too late to fix, at night, towing a strange trailer, sideways rain, etc etc.

 

[ohmman]

OK, I've received the trailer and was finally able to test. Results:

Car "off" meaning key not in proximity: 11.8VDC-12.8VDC (fluctuating slowly)
Car in Neutral with Parking Brake engaged: 13.8VDC constant
Car in gear: I couldn't test without killing myself. I was alone.

Any idea why I'd be getting the first result? Is that going to be enough to trickle to the trailer? Clearly the second option is quite enough. I forget how long the car stays "alive" when one does this. Input on that?

This may not be my end game, but it's a solid workaround for anyone with an X in a pinch.

 

[Fresh Start Detail]

OK, I've received the trailer and was finally able to test. Results:

Car "off" meaning key not in proximity: 11.8VDC-12.8VDC (fluctuating slowly)
Car in Neutral with Parking Brake engaged: 13.8VDC constant
Car in gear: I couldn't test without killing myself. I was alone.

Any idea why I'd be getting the first result? Is that going to be enough to trickle to the trailer? Clearly the second option is quite enough. I forget how long the car stays "alive" when one does this. Input on that?

This may not be my end game, but it's a solid workaround for anyone with an X in a pinch.

I believe that the 11.8-12.8v you're seeing is enough to "trickle to the trailer", but it's more a question of the amps that will be delivered, the wiring sizing, length to the battery etc., things you've already mentioned so you're obviously aware.

 

[idoco]

OK, I've received the trailer and was finally able to test. Results:

Car "off" meaning key not in proximity: 11.8VDC-12.8VDC (fluctuating slowly)
Car in Neutral with Parking Brake engaged: 13.8VDC constant
Car in gear: I couldn't test without killing myself. I was alone.

Any idea why I'd be getting the first result? Is that going to be enough to trickle to the trailer? Clearly the second option is quite enough. I forget how long the car stays "alive" when one does this. Input on that?

This may not be my end game, but it's a solid workaround for anyone with an X in a pinch.

The 11.8V-12.8V is what I would expect to see from just the accessory battery. The lower end being either sag from the battery under load or a mostly discharged battery.

13.8V looks to be output from the DC converter. 12V batteries generally charge at 14V +/-.

If "off" is just the 12V accessory battery you're going to discharge it unless the car constantly monitors the accessory battery and turns on the DC/DC converter even when off.

 

[ecarfan]

If "off" is just the 12V accessory battery you're going to discharge it unless the car constantly monitors the accessory battery and turns on the DC/DC converter even when off.

I believe it is true that the 12V battery is recharged by the car (it has to or the 12V battery would have a very short lifespan in a Tesla) but not sure if that recharging happens when the car is in the "off" condition.

 

[idoco]

I believe it is true that the 12V battery is recharged by the car (it has to or the 12V battery would have a very short lifespan in a Tesla) but not sure if that recharging happens when the car is in the "off" condition.

The DC/DC converter charges the 12V accessory battery when the car is on. When the car is off the DC/DC converter is turned off. Periodically the DC/DC converter will turn on to "top off" the 12V battery in order to keep the vampire drain of the 12V circuits from draining the accessory battery.

This thread seems to confirm the cycling of the DC/DC when the car is off. The question I have is whether this cycling is time dependent or voltage dependent. In other words does it recharge periodically or on demand.

If the periodically then there is a chance that the extra load could drain the 12V battery in between cycles. If on demand then I think less likely.

Regardless, if the purpose is to charge the trailer battery when the car is off it's not going to work. 12V won't cut it. The voltage needs to be higher to charge a deep cycle agm battery (14.5'ish for charging, 13.8'ish for float).

 

[ecarfan]

if the purpose is to charge the trailer battery when the car is off it's not going to work. 12V won't cut it. The voltage needs to be higher to charge a deep cycle agm battery (14.5'ish for charging, 13.8'ish for float).

Okay thanks. So it appears that one could charge a 12V trailer battery while towing with an X. Which could be helpful for many people.

I plan to cover the roof of my camper trailer (taking delivery spring 2018) with solar panels so most of the time won't need to charge the trailer battery while towing...except when its raining.

 

[ohmman]

A note - leaving the 7-pin adapter connected to the car while the car is parked/off and the trailer has no shore power will result in a significant drop in range. How significant? On the order of 30-40 miles overnight!

I thought I noticed this on my first boondocking trip with the camper, but then second guessed my memory. However, on this recent trip I have confirmed it. I suggest anyone with a trailer disconnect the 7-pin while camped overnight. It's far too lossy to be worthwhile.

 

[animorph]

Could it be a good source of always on 12v for external use? Seems like a bunch of guys looking for that for various reasons, without success. For example, powering a telescope without having the car (and lights) on.

 

[idoco]

A note - leaving the 7-pin adapter connected to the car while the car is parked/off and the trailer has no shore power will result in a significant drop in range. How significant? On the order of 30-40 miles overnight!

I thought I noticed this on my first boondocking trip with the camper, but then second guessed my memory. However, on this recent trip I have confirmed it. I suggest anyone with a trailer disconnect the 7-pin while camped overnight. It's far too lossy to be worthwhile.

Certainly running A/C via the inverter or other 110v systems through the inverter could cause that draw. But I'd be surprised if the wiring of the harness and the fuse is capable of handling the required current.

30-40 miles at 550Wh/mi (with trailer) would be ~15-20 kWh. Using the lower end, over 10 hours that draw is 1.5kW each hour. So a 1500 watt use in an hour would require an ~100 amp current flow at 14v through the harness. That would require roughly 6-10 ga wiring. Quick search seems to suggest that most of the 7-way SAE connectors use smaller wire and are fused at 15amps DC.

Based on my calculations the fuse should blow way before the wiring fried.

 

[SageBrush]

Certainly running A/C via the inverter or other 110v systems through the inverter could cause that draw. But I'd be surprised if the wiring of the harness and the fuse is capable of handling the required current.

30-40 miles at 550Wh/mi (with trailer) would be ~15-20 kWh. Using the lower end, over 10 hours that draw is 1.5kW each hour. So a 1500 watt use in an hour would require an ~100 amp current flow at 14v through the harness. That would require roughly 6-10 ga wiring. Quick search seems to suggest that most of the 7-way SAE connectors use smaller wire and are fused at 15amps DC.

Based on my calculations the fuse should blow way before the wiring fried.

I had similar thoughts. Perhaps the car is wasting energy ?

 

[ohmman]

Certainly running A/C via the inverter or other 110v systems through the inverter could cause that draw. But I'd be surprised if the wiring of the harness and the fuse is capable of handling the required current.

30-40 miles at 550Wh/mi (with trailer) would be ~15-20 kWh. Using the lower end, over 10 hours that draw is 1.5kW each hour. So a 1500 watt use in an hour would require an ~100 amp current flow at 14v through the harness. That would require roughly 6-10 ga wiring. Quick search seems to suggest that most of the 7-way SAE connectors use smaller wire and are fused at 15amps DC.

Based on my calculations the fuse should blow way before the wiring fried.

30-40 miles of rated range are still at 320Wh/mi. It doesn't adjust rated miles when the trailer is attached. So 30-40 miles is actually about 9.6-12.8kW. Still quite a bit, but not as high as what you were stating. Additionally, the timeframe was from parking at camp (about 5pm) until departing from camp (about 9am). So that's 16 hours.

I'm not sure exactly why this occurs, and agree that it seems like an awful lot. One explanation is that the car may not sleep, so vampire drain is exacerbated.

 

[JimVandegriff]

I'm not sure exactly why this occurs, and agree that it seems like an awful lot. One explanation is that the car may not sleep, so vampire drain is exacerbated.

One really interesting experience we had on our last trip was waking up in the morning to a camp host telling us that our car had its lights on all night. We realized that the key fob for the car was in our clothes in the trailer within range of the vehicle (they were not unhooked), and that the vehicle did not shut down during the night. After that incident, we made a place to put the fobs in the bathroom so it was far enough away from the vehicle to allow it to "sleep". Jim

 

[ohmman]

One really interesting experience we had on our last trip was waking up in the morning to a camp host telling us that our car had its lights on all night. We realized that the key fob for the car was in our clothes in the trailer within range of the vehicle (they were not unhooked), and that the vehicle did not shut down during the night. After that incident, we made a place to put the fobs in the bathroom so it was far enough away from the vehicle to allow it to "sleep". Jim

We are sensitive to this as well, mostly because my wife is worried that someone might "drive away with us."

 

[idoco]

A note - leaving the 7-pin adapter connected to the car while the car is parked/off and the trailer has no shore power will result in a significant drop in range. How significant? On the order of 30-40 miles overnight!

I thought I noticed this on my first boondocking trip with the camper, but then second guessed my memory. However, on this recent trip I have confirmed it. I suggest anyone with a trailer disconnect the 7-pin while camped overnight. It's far too lossy to be worthwhile.

Ran across this in the Edmond's Model X towing article (a reply by author in the comment section):

"I do know that I left the rig parked for two days while I attended to my Ram duties. The car was off, the trailer lights were off, and I did not unplug the 7-pin connector while it sat for 48 hours. No loss of range doing that." [emphasis added]

Towing a Teardrop Trailer to Flagstaff - 2016 Tesla Model X Long-Term Road Test

 

[ohmman]

Ran across this in the Edmond's Model X towing article (a reply by author in the comment section):

"I do know that I left the rig parked for two days while I attended to my Ram duties. The car was off, the trailer lights were off, and I did not unplug the 7-pin connector while it sat for 48 hours. No loss of range doing that." [emphasis added]

Towing a Teardrop Trailer to Flagstaff - 2016 Tesla Model X Long-Term Road Test

Interesting. I'll do a driveway test next week at some point and report back. I was going to say that he was probably hooked up to shore power, but it doesn't appear that was the case.

 

[idoco]

Interesting. I'll do a driveway test next week at some point and report back. I was going to say that he was probably hooked up to shore power, but it doesn't appear that was the case.

Bump on thread. Did you get a chance to perform this test?