Hello,
I am helping with a build of a 1972 Boler 13' camper.
The tow vehicle has a factory tow package including a 7 pin trailer connector.
The trailer has a 12 volt flooded lead battery. It is currently charged by an external battery charger.
The current refrigerator is a 120 AC.
The thought is to swap it out with a 12 Volt refrigerator. We will have a 120 -> 12 Volt converter to charge the battery and run the refrigerator.
Can I hook up the charge line from the tow vehicle directy to the battery ? I would put in a fuse.
When we change to Lithium battery(s), I assume I would need a proper 12v ->12 volt charger?
Mark
One of the 7 pins is for exactly that.
Don't remember what color. 7 pin flat (90 + % of RVs) is different than 7 pin round (tractor trailer) and different than 4 pin.
Blue is for trailer brakes (heavier gauge than lights)
Center post is for back up lights.
the power on the 7 pin will be the heavier gauge as well.
if ya google-fu trailer wire chart, you'll find it.
If not, I'll look it up.
I re read the question closer. Yes I would imagine a new ish factory 7 pin would be set up to hook direct to camper to charge. Wouldn't need an additional fuse. No harm in adding a fuse at camper, sized to amp capacity of wire gauge.
WRT the lead battery, no conversion needed to charge it, but you need to make sure the wires are heavy enough. And that it won't drain the car battery when not driving
For the conversion to lithium, you will need a dc-dc converter that is set up to charge the different chemistry. We have one from renogy for our camper- but my 12v was too little from the escape. Need to update that.
But since our 12v fridge can run for over 24 hours on the battery alone, I don't really need to charge it while driving. Once we stop to camp, plugging in charges the battery.
In reply to alfadriver :
My experience is like yours; just charges on shore power has worked for me.
I stopped at lithium, since I have not learned enough yet!
BTW, what is "WRT".? Thanks.
The +12 on the trailer 7-pin is really for charging the little teeny batteries that many trailers use to power the electric brakes when the emergency breakaway switch is pulled. Personally I'm not comfortable using it to charge a big lead/acid battery because if that battery is really low it may suck down enough current to pop the fuse in the tow vehicle.
You can get DC/DC chargers that will limit the amount of current being used to charge one 12V battery off another 12V system, they're often sold for charging your RV starting battery from the house battery system. Putting one of those on the supply line from the truck will fix this problem.
IMHO though, far and away the best way to charge trailer batteries is solar. Put a couple panels on the roof (how many depends on your expected needs), install a solar MPPT charger, and whenever the trailer is outside in the sunshine it's charging. Nothing to remember, nothing to think about, it's just always charged.
Have you considered a small solar setup?
Check your 12v pin in the connector of the tow vehicle. Some of them are just hot all the time, but I've had some that were on a relay that turned off when the key was off. This was for exactly that reason. If you stop for the night and drain the RV battery, it won't drain the tow rig battery. Just suggesting that you check so you know if you should unplug when you stop for the night.
As others have said, there is a 12v+ pin in the connector for exactly that reason. Many states require having a battery with a breakaway switch for the brakes above a certain GVWR, so the 12v pin is there to ensure it stays charged.
In reply to Curtis73 (Forum Supporter) :
Had not thought to mention that current to charge a big drained battery could be a problem, till the one guy did, but it's worth repeating here.
the newer stuff with the relay so not hot all the time , are prolly "smart" enough to not burn wires. All ways on? Better be safe.
I understand there is a change line from the tow vehicle. Every factory tow package I have seen turns off when the key is off.
I was just making sure that I could connect the charge line directly to the battery without some other device. I would hate to wire this up and get a call saying the tow vehicle is not charging.
I will not need to use the brake line for the Boler. It only weighs 800 lbs unloaded.
Mark
WRT - With Respect To
I would be cautious about repurposing an existing terminal. The nice thing about standards is that they are standardized.
There is no reason one could not run a second cable. A two pin generic connector would be great for this. Plus it gives you the option to unplug it while leaving everything else live, should the need arise. Backfeeding might be an issue, though, it could keep the tow vehicle powered up through the 7 pin's switched battery feed. There is probably a simple solution for this.
In reply to Pete. (l33t FS) :
Thanks.
I can ask on here; I have to get a translator for ads on market place 
Oh boy something that is right in my wheelhouse.
The comments of suggesting a DC/DC charger or isolator are spot on. You can limit the current bring brought in with those and will keep your modern vehicle systems happy.
The simplest way to get a house battery in your camper is to use a Goal Zero or Jackery or similar, wire up as follows:
-DC from your tow vehicle on the charge pin can either be run to a DC-DC charger OR direct to the solar inputs on the Goal Zero depending on what your incoming voltage is (GZ needs a higher input voltage that some vehicles with modern alternators support, the off brands of solar generators are less picky it seems)
-DC from your battery can be used to run your fridge when you are on shore power or travelling. Using AC power on an AC/DC fridge is a waste of electrons.
-Use your existing AC charger that came with your Goal Zero or similar to charge up the battery when you have 120VAC available. You can use the 120V as a pass-thru and still use your GZ for all your AC and DC needs when you have shore power, my 1000WH Lithium does 10A of 120 with a 15A surge which is plenty.
-You can add solar if you will be boondocking for multiple days without driving but its not totally needed if all you want to do is run a 12V fridge for a weekend especially considering you are driving too camp on Friday and driving home on Sunday. 100 watts of solar would be plenty for just a fridge.
-My ARB Elements 60L compressor fridge runs 3-4 days in 70 degree weather on a 1000 watt-hour Goal Zero lithium. My GZ charges at a rate of about 10%/hour on either the 120VAC or the 12VDC. You can get a fast charger if needed but 10%/hour is really pretty good.
In theory, the +12V is capable of 20A. But the vehicle needs to be set up to do that.
Pete. (l33t FS) said:
I would be cautious about repurposing an existing terminal. The nice thing about standards is that they are standardized.
I would use the existing change line in the standard 7 Pin trailer connector.
Mark.
In reply to 93gsxturbo :
Thanks 93gsxturbo!
I am looking at this unit. It will fit just under the seat in the camper.
BLUETTI Portable Power Station AC180, 1152Wh LiFePO4 Battery Backup w/ 4 1800W (2700W peak) AC Outlets, 0-80% in 45 Min., Solar Generator for Camping, Off-grid, Power Outage
Would you recommend a Goal Zero over a Bluetti. I need to be able to use a coffee maker and 1000 watts does not cut it.
Mark L
The Blue Titty seems to have some real nice specs for the money. At the end of the day its just a battery in a box, there are only some many ways to screw it up. Bluetti is a mainstream brand so I would have no hesitation.
To me the driving factor is form factor, thats what got me to the Goal Zero. The other ones I looked at I (Jackery, Anker) did not have as nice of a form factor.
If this one has all the right plugs for you and is the shape you can use, then its a winner.
The 12V, 10A input is nice, it will be a bit slow on the charge considering the capacity, (not slower than anything else at 12V, 10A just that its a big box to fill at 10A) but it wont overload any existing 12V wiring or need any other geegaws.
Get it and if its not what you need, return it. Try charging it off your vehicles power ASAP, some MPPT are more sensitive than others and wont charge under 14.5 volts which not all vehicles output, regardless of what is printed on the box.
