DC to DC Charger from Truck to Trailer

[mattkrea]

Hey all,

New here but I checked all 32 pages of the electronics section and saw nothing that appeared to answer this. Dual battery setups get close but not quite there for the specific question I need to figure out.

I'm purchasing an Airstream Basecamp and am installing 6 Battle Born batteries in it. I'll have solar but that's effectively just a trickle charge and want to have a fairly high amp charge from the main vehicle while driving. I've heard from a ton of people (including Jeep service teams) that I need to be careful wiring in and that the Jeep electrical system should work fine but needs to know what you are pulling from the battery because it is a "smart" alternator.

Now, my model has the 240 amp alternator as I understand it so I should be able to get away with pulling from it but I do not know where this common negative point to pull from is. Is it a chassis ground point? Or is it some shunt-like connection between the primary battery and the secondary? I've been told by several people that I definitely do not want to connect right to the normal terminals on the main battery.

Any ideas on this? Am I way overthinking this? Thanks in advance.

Vehicle is a '21 Jeep Gladiator Rubicon 3.6.

(Also attached a diagram from the awesome team at Redarc but its a little vague as far as connection points on the tow vehicle go..)

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[Mr._Bill]

With the Solar panels, there should be a charge controller for the battery bank that will have an input for the 12v feed from the 7 pin connector. The draw from the controller should not be more than the Jeep electrical system can handle, and with a good controller the demand should be adjustable.

The common negative point is the frame. Make sure that everything is properly grounded, and that the connections are well done.

 

[just_another_guy]

Am I way overthinking this?

Pretty much, yes.

It's a "smart" alternator in the sense that it varies the output voltage, but if you are running it through a dc-dc charger that issue is taken care of. The chassis is grounded so as long as you make a solid connection to it you'll be fine.

If you install it per the diagram you supplied, the system will be fused, isolated when the key is off, and supplying the correct voltage/amperage to your house batteries via the charge controller. Looks like a great setup to me.

 

[Radio Guy]

There appears to be a current shunt for the vehicle computer on the large battery negative terminal and I believe the common ground point is where the ground wire from the larger battery connects to the vehicle chassis near the battery. I do a lot of solar and vehicle wiring and your diagram looks ok to me.

One thing I would verify is when you go to start the vehicle is the isolation relay on the left side of your diagram going to engage causing the trailer batteries to share the starting current? That could be a problem if the vehicle batteries are drained and the trailer batteries are topped off causing a lot of current to flow on the long interconnect cable between vehicle and trailer.

If you have the optional power switch cluster you could use one of the low current switches and run that to the relay coil of the isolation relay and program for power when ignition is on, then manually turn it off when starting the vehicle. That would disconnect the trailer batteries from the vehicle when parked and give you control over when the vehicle charges the trailer.

 

[mattkrea]

Thanks for the help guys. I'll likely wire in some manual control over that current as you suggest so that I can optionally disable the charging of the trailer when I need to.

 

[Radio Guy]

Another option would be a high current Schottky diode in series with the cable to the trailer. A Schottky has very low voltage drop and that would allow only charge current to flow towards the trailer and the trailer batteries would be prevented from starting the vehicle. You could also use a battery isolator between the alternator and vehicle battery/trailer battery which would accomplish the same thing.

Thanks for the help guys. I'll likely wire in some manual control over that current as you suggest so that I can optionally disable the charging of the trailer when I need to.

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