Maintaining Trailer/Camper Battery with 7-Pin AUX output

[dmurphy]

Did not. But I do need the LED adapter.

I apologize for asking because I’m sure you’ve described it in exquisite detail but I just can’t find it ...

Do you know what the “behavior” of the AUX pin is on the Raven? Is it providing 12V while the vehicle’s in motion? Stationary?

Just curious if and how I can use it to top off the 12V system on the trailer once it arrives. Our camper comes with a 12V compressor fridge - Max 5.7a draw. Would love to leave it running while in transit, and still keep the 12V battery topped off.

Debating upgrading the minuscule 85w solar panel it comes with - seems like it’s almost a waste of space. Will check wire gauge once I get the thing and see how big we can get. Would love to replace it with a residential 300W panel.... and add a second.

 

[ohmman]

I apologize for asking because I’m sure you’ve described it in exquisite detail but I just can’t find it ...

Do you know what the “behavior” of the AUX pin is on the Raven? Is it providing 12V while the vehicle’s in motion? Stationary?

Just curious if and how I can use it to top off the 12V system on the trailer once it arrives. Our camper comes with a 12V compressor fridge - Max 5.7a draw. Would love to leave it running while in transit, and still keep the 12V battery topped off.

Debating upgrading the minuscule 85w solar panel it comes with - seems like it’s almost a waste of space. Will check wire gauge once I get the thing and see how big we can get. Would love to replace it with a residential 300W panel.... and add a second.

I haven't checked on this vehicle, but I can try at some point. The duty cycle on your fridge will probably be low enough that the 7-pin could nearly cover it. But I wouldn't rely upon it.

If I had a compressor fridge (I don't, my year of Airstream has an absorption fridge), I would invest in lithium batteries and ensure I had plenty of storage to cover me between hookups. And, as you say, improve the rooftop solar situation. But I'll say that @idoco has reported some success with the 7-pin as a power source, and may have a different opinion.

 

[idoco]

Our camper comes with a 12V compressor fridge - Max 5.7a draw. Would love to leave it running while in transit, and still keep the 12V battery topped off.

We have a Nova Kool, 12VDC fridge. It draws ~3.5-4.5A when running.

Here's a link to a post I wrote about using the 7-pin as a supplemental power source.
Ohmman's Airstream Adventures

 

[dmurphy]

I haven't checked on this vehicle, but I can try at some point. The duty cycle on your fridge will probably be low enough that the 7-pin could nearly cover it. But I wouldn't rely upon it.

If I had a compressor fridge (I don't, my year of Airstream has an absorption fridge), I would invest in lithium batteries and ensure I had plenty of storage to cover me between hookups. And, as you say, improve the rooftop solar situation. But I'll say that @idoco has reported some success with the 7-pin as a power source, and may have a different opinion.

I'm in love with the idea of the 12V compressor fridge; ours is a Norcold Polar N10DC. (I notice they avoided calling it the DC10. Bad juju.). That said, I want to see how it does in the practical world.

I don't plan to do much dry camping; most of what we do will be on-grid somewhere. But in between those hookups, I'd like to keep the battery somewhat stable. The Norcold claims about a 25% duty cycle @ 5.7a, so that's around 34Ah daily.

Between a decent solar array, a decent LiIon battery (I'm thinking about a pair of Ohmmu - any relation @ohmman? - battery in parallel; their Tesla replacement batteries seem high quality, at least...) - and at least some juice from the 7-pin, I think I'd be more than fine. Each of the Ohmmu batts is rated for 150Ah so that's 300Ah to burn through assuming it's cloudy days and the Model X can't supply any juice.

Should be plenty.

We have a Nova Kool, 12VDC fridge. It draws ~3.5-4.5A when running.

Here's a link to a post I wrote about using the 7-pin as a supplemental power source.
Ohmman's Airstream Adventures

Thanks for the link! Did you do anything with a buck-boost yet? Our batts will be on the tongue so I don't have the same voltage drop issue you would, but even at that, 13V is fairly low.

 

[idoco]

Did you do anything with a buck-boost yet? Our batts will be on the tongue so I don't have the same voltage drop issue you would, but even at that, 13V is fairly low.

Not yet. I may try one other thing first. Our OEM solar connection is right next to the battery box, near the rear of the trailer. I want to try a connector from the 7-pin on the MX to the 2-pin solar connection to see what happens to the voltage drop and amp draw capacity. If I can park next to or behind the trailer I can use a shorter cord.

 

[dmurphy]

Not yet. I may try one other thing first. Our OEM solar connection is right next to the battery box, near the rear of the trailer. I want to try a connector from the 7-pin on the MX to the 2-pin solar connection to see what happens to the voltage drop and amp draw capacity. If I can park next to or behind the trailer I can use a shorter cord.

Interesting thought! Don’t see why that wouldn’t work ... The 13V output from the aux pin really would look just like a solar panel to the charge controller, wouldn’t it?

 

[idoco]

Interesting thought! Don’t see why that wouldn’t work ... The 13V output from the aux pin really would look just like a solar panel to the charge controller, wouldn’t it?

Actually the external solar connector is a fused connection that leads directly to the 12V battery. The output of the solar charge controller would go to the battery via the external solar connector. Since I don't have solar (just the connection point) I don't have a charge controller. The only advantage would be that it cuts down on the wiring length.

But using a charge controller as a DC/DC converter is an interesting idea. I'll have to look at input and output specs.

 

[dmurphy]

Actually the external solar connector is a fused connection that leads directly to the 12V battery. The output of the solar charge controller would go to the battery via the external solar connector. Since I don't have solar (just the connection point) I don't have a charge controller. The only advantage would be that it cuts down on the wiring length.

But using a charge controller as a DC/DC converter is an interesting idea. I'll have to look at input and output specs.

Gotcha. Our Surveyor has a charge controller preinstalled with an 85W panel. Any external solar ports would be inputs to the controller; in my case I’d use MC4 splitters. I’d think in any solar setup you’d want an intelligent controller to smooth the voltage coming from the photovoltaics; the one we have has settings for AGM, wet, lead carbon or LiFEPO4 batts. Basically it just manages the charge cycles - boost, float or equalizing (obviously don’t want the equalizing for a lifepo4.). Would basically be your buck-boost idea on steroids. And fairly cheap; the 10a controller we’re getting with ours is less than $75 retail. I’m sure there’s better ones on the market but Forest River isn’t known for spending excess anything on anything.

https://www.amazon.com/dp/B00HSNZFSO/

 

[idoco]

...Would basically be your buck-boost idea on steroids...

Good thought. But I don't think it will work.

Solar panels output at 17V+. My understanding is that solar charge controllers requires at least a 5V differential between the input voltage on the solar side and the output voltage on the battery side. Since the 7-pin output is ~14.5V max (13.5-13.8 after sag) the controller won't function. I think it is meant as more of a DCDC buck rather than DCDC boost.

What I'm looking at are DCDC battery chargers and converters. They are meant to boost voltage from either an alternator or battery input.

The first type takes a 12V (11V-15V) input and boosts to a higher voltage output for charging the batteries. They are "smart" and perform three stage charging. Two examples are https://www.victronenergy.com/uploa...Smart-DC-DC-chargers-isolated-250-400W-EN.pdf or 12V DC to DC On-Board Battery Charger.

The problem with these are that the output is constant (lowest outputs are ~220W and ~250W respectively). This is probably over the limit of the wiring and fusing (15A) on the 7-pin harness. Also, when added to the normal DCDC load requirements, possibly pushing the limit of the DCDC converter in the MX.

The second choice would be a straight DCDC converter. No smart battery charging profiles. Just a constant output voltage. One option is https://www.victronenergy.com/uploa...DC-DC-converters-isolated-100-250-400W-EN.pdf.

The 12/12-9A (110W) would fit the requirements. 110W should be well within the fusing of the 7-pin. Input and output voltages are ideal. The only downside is that because the output voltage is fixed it is essentially a "dumb" charger. No staging of charging as the battery SOC changes. This means I would need to keep a closer eye on the battery SOC in order not to overcharge.

Ideal would be option #1 with a lower constant output power or adjustable output power. Option #2 is ok out of the box. Better if I could figure a way to make it "smart".

P.S. @ohmman Sorry to hijack your thread. Don't know if you want to break it out to a separate thread.

 

[ohmman]

P.S. @ohmman Sorry to hijack your thread. Don't know if you want to break it out to a separate thread.

Done.

I'll add a note that we all have a very capable DC-DC converter with us when we're towing. It's in the X and charges/maintains the 12V system. I've considered tapping into it before with my 90D, but gave up on that idea, worrying about depleting my tow vehicle. The idea would be to tap into the 12V system in the frunk and run heavier wiring back to the rear of the vehicle with a quick disconnect fitting. The camper would have a similar quick disconnect fitting, and I'd connect them at camp with another length of wire.

The idea is worthwhile, in my opinion, but it poses the same issue every time I think about it - when I'm in a location where my camper doesn't have shore power, we are more than likely in a location where the car doesn't have charging ability. So the idea of drawing down the car battery, no matter how little, is counterproductive to me. In most summer and shoulder season camping, my batteries and solar outlast my holding tanks by a long shot. We can make 5 nights at best boondocking before our tanks are full.

I might feel differently if I move to a compression fridge, but even then I'm doubtful it'd matter much.

 

[idoco]

when I'm in a location where my camper doesn't have shore power, we are more than likely in a location where the car doesn't have charging ability. So the idea of drawing down the car battery, no matter how little, is counterproductive to me.

That makes perfect sense...especially since you have solar capacity. Our experience is that the power used by keeping the trailer connected does not result in much energy loss. Maybe a couple percent over a few days. Almost indistinguishable from vampire drain.

We generally can justify the energy consumption with our boondocking strategy...the "fifty mile radius rule". Basically we can boondock within fifty miles of a supercharger.

And even further if there is any level two/three charging around. We'll just take the MX into town, opportunity charge for a few hours while we shop, hike, eat, grocery shop, etc.

In most summer and shoulder season camping, my batteries and solar outlast my holding tanks by a long shot. We can make 5 nights at best boondocking before our tanks are full.

Agree that tanks are more of a limiting factor. Not insurmountable.

On the water supply side I periodically top off our freshwater tank during trips. I have a couple collapsable bags that I can carry to any nearby communal water supply.

On the waste side we have a five gallon Thetford cassette as the black tank. The great thing about the cassette is that it is easily transportable, including telescoping handle and wheels (think carry on luggage). I can dump at any nearby dump station, campground toilet, or vault toilet.

Which leads to the grey water. Our twenty one gallon is fixed. But the black water cassette also acts as a Blue Boy tote. After dumping the black water I can offload grey water into the cassette and dump in a toilet or vault. Usually it is walking distance. Sometimes I'll use the hitch carrier tray if not in walking distance (X-One Cargo Carrier for Tesla Model X (Black) | Cargo carrier specifically designed for the Tesla Model X | X-Rack)

 

[Richbot]

Done.

I'll add a note that we all have a very capable DC-DC converter with us when we're towing. It's in the X and charges/maintains the 12V system. I've considered tapping into it before with my 90D, but gave up on that idea, worrying about depleting my tow vehicle. The idea would be to tap into the 12V system in the frunk and run heavier wiring back to the rear of the vehicle with a quick disconnect fitting. The camper would have a similar quick disconnect fitting, and I'd connect them at camp with another length of wire.

The idea is worthwhile, in my opinion, but it poses the same issue every time I think about it - when I'm in a location where my camper doesn't have shore power, we are more than likely in a location where the car doesn't have charging ability. So the idea of drawing down the car battery, no matter how little, is counterproductive to me. In most summer and shoulder season camping, my batteries and solar outlast my holding tanks by a long shot. We can make 5 nights at best boondocking before our tanks are full.

I might feel differently if I move to a compression fridge, but even then I'm doubtful it'd matter much.

I've always just thrown gas on this problem, but this is one of those questions a dual-battery setup like many 3/4-tons come optioned with for trailer people is perfect for, with switched power/charge. With a couple minor uh...tweaks...to the frunk (I think it probably would need some clearancing of the frunk liner/bin/bucket assembly to make room for a second battery) you could probably make a dual-batt holder work up front on the X.

I've also seen people just use a cargo-area 12v outlet to keep charge on a large AGM deep-cycle while the car is moving, and use a pigtail of appropriate gauge attached to the posts, with quick connector at the end fished through the rear trim down by the drawbar to allow hookup to the trailer, and I've seen people put the big battery on their trailer tongue if they have the space and tongue/trailer weight to spare.

 

[idoco]

Resurrecting an old thread...charging a trailer from the MX 7-pin connector.

Previously I had been charging the trailer from the MX via the trailer 7-pin wiring. This wasn't ideal since the trailer wire gauge, combined with the run length to the battery, resulted in a a voltage drop (13.5V --> +/-12.7V). Via this route the MX could provide no more than ~3A-5A. Since the 7-pin is fused for 15A and the MX DC/DC converter can probably put out +/- 200A, I wanted to get more out of the system.

In order to tweak the charging I ended up getting a 110W, 12V/12V, DC/DC converter. Additionally instead of using the trailer 7-pin wiring I have made 12ga wire to connect the MX 7-pin to the DC/DC converter. Finally, I am using the Zamp solar connector on the trailer as the battery connector. This directly connect to the DC buss in the trailer.

The DC/DC converter output voltage is adjustable. I have it set to the float voltage for my AGM battery (13.8V).

With the above I'm seeing almost 10A at the trailer battery during charging! Given that we use ~20Ah a day (a bit more when it's cold), I can run the above setup a couple hours every few days to keep the trailer charged.

One downside of this setup is that the DC/DC converter is not a charger. It does not have staged charging abilities. It just dumps energy into the battery. So I have to keep an eye on it while charging. The reason I'm not using a DC/DC charger is that even the smallest has a power draw greater than the MX 7-pin capability.

I did try using a PWM solar charge controller as a smart charge regular. Feeding the controller with the DC/DC converter output. The DC/DC output turned up to the max (15.3V) is within input specs for the solar controller.. Basically trying to trick the controller into thinking the DC/DC was a solar panel.

For whatever reason the charge controller would keep cycling on and off. Never putting out much current. I decided it wasn't worth my time to play with that any more. Maybe a 12V--> 24V DC/DC might work. Or an MPPT solar controller.

In any event, we'll be boondocking outside the Grand Canyon in a couple weeks. We won't have any hookups so this should be a good solution for our power requirements. Now I just have to fine tune our fresh water and waste water strategy.

 

[ohmman]

Now I just have to fine tune our fresh water and waste water strategy.

I have a 30 gallon version of this: Aquaflex.net - Aquatank II - Emergency Water Storage Tank Bag - Aquatank Portable Water Storage Bags. They sell them on Amazon and directly. Useful for extending your fresh water capacity without having to store a bulky jug or set of jugs.

I think you have a cartridge toilet so I don't have recommendations for that side of things.

 

[idoco]

I have a 30 gallon version of this: Aquaflex.net - Aquatank II - Emergency Water Storage Tank Bag - Aquatank Portable Water Storage Bags. They sell them on Amazon and directly. Useful for extending your fresh water capacity without having to store a bulky jug or set of jugs.

I think you have a cartridge toilet so I don't have recommendations for that side of things.

I was looking at those. Put that would mean also getting a pump since 250 lbs of water is a little heavy to lift.

I ended up getting several of these smaller, foldable containers (5 gallons each). Should be a little easier to handle and store. I plan on filling them at the Mather campground and transporting them back to the trailer on the hitch cargo rack.

 

[ohmman]

Put that would mean also getting a pump since 250 lbs of water is a little heavy to lift.

Yes, I have a pump. You could theoretically use your fresh water hose and park the car much higher than your water tank..

Sounds like you've got it solved.

 

[idoco]

Yes, I have a pump. You could theoretically use your fresh water hose and park the car much higher than your water tank..

Elon needs to add one more setting to the air suspension