I'm going to set up to charge my 5er batteries from my truck alternators. I will put in an anderson quick connector by the in bed trailer connectors.

First, is 6 gauge wire sufficient for this distance at say 60Amps? I plan to use a Vistron 30Amp charger but they are stackable so I want some leeway.

Second, do I have to run both possitive and negative from the battery or would it be ok connected the negative to a good ground back by the connector?

 

Using this calculator

https://www.omnicalculator.com/physics/dc-wire-size

Nominal 14V at 60 amps over 50ft 1 way would require 4/0 copper wires, assuming up to 3% voltage drop is allowable.

Scale that back to 30 Amp and you can use 1/0 copper.

Reduce the run to 25 feet and 30 amps, you can use 3 AWG.

 

The answer you want on wire size is in the post above. The numbers that Stuart used were a bit more conservative that I normally use. For example, a 60 amp DC-DC charger is going to draw more than 60 amps from the alternator. Maybe as much as 80 amps and you have to take that number into account when calculating the wire size. In general, high DC-DC charge rates from a tow vehicle to a trailer are cost prohibitive.

I disconnected the 7-pin charge to my LiFePO4 battery bank in my trailer. I didn't like the charge profile that the truck would have provided. The PV on my trailer provides plenty of charge. However, if I were to need a charge from the truck, I would limit it to using an 18 amp DC-DC charger so I can use the 7-pin and not have to run new cable.

With regard to running both positive and negative cables, my opinion is to run both. Copper is a better conductor than steel. The counter argument is that there's a lot of steel to conduct through. You'll have to clear paint and rust protection from the frame at some spot if you rely on the frame for the negative. In terms of effort, running two cables is just a little more work than running just one cable.

 

Here's a . I plan to modify this somewhat when I get our RV.

Some good info in this post. @HRTKD contributed some great reference material there...

 

I used 4 gauge wire for my Renogy 40amp charger. It was per the installation instructions. It works fine.

I ran both positive and negative cables from the battery (positive side was via a circuit breaker and a solenoid so I could control when/if I wanted to charge the batteries with an up fitter switch). But if I did it again I would find a Ford grounding point on the frame near the rear.

My alternators are happy and the battery charge is good. On short trips I don't bother charging my 200ah Lithium battery as I figured it is a good exercise to use the battery occasionally (or more often).

 

I used 2 gauge for a 40 amp (Renogy) system. Wired through upfitter #1 via a terminal block fuse and a Cole Hersee relay. Ground on the rear frame of the truck. We have 3 - 100w panels on the roof of the rig, but, we only saw sun one day on the last trip (12 days). It is nice to know that the battery bank (3 - 105ah AGM's) will be full when we get to our destination.

 

That's my concern. Our 5er has 400W of solar but our first major destination is Fairbanks so I'm not expecting the solar to do a lot for us.

 

If you go to Fairbanks, in June-July, the sun Is out 20hrs a day!

 

Very low on the horizon though. I don't think solar works very well that way. Maybe I could bring some stand up panels.

 

no it's really high in the summer, low in the winter

 

I have this same scenario but for a travel trailer, not a 5er. This is what I did. I ran a 1/0 welding cable from the passenger battery to an Anderson connector that is mounted in a Trailer Vision socket. The negative side of the Anderson connector is a 1/0 cable that routes up to the frame. I made the cable with glue-impregnated heat shrink to seal it up against moisture and such. I ground a spot clean on the hitch where an existing hole was and used a stainless bolt and washers to crush the cable lug against it. I then painted over the entire connection point. That was almost two years ago and I have zero corrosion issues.









I have used this connection point to jump start cars with completely dead batteries and to run a winch slid into the receiver on a cradle. I've had zero issues with current flow. The frame might be steel but it is large - and it has low resistance because of its size. I will recommend that you upgrade the ground from the battery to the frame of the truck to help handle the increased current flow. There is a factory ground on top of the frame almost directly below the battery tray on the passenger side. I made a 1/0 ground cable and installed it right over top of the factory ground.


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This setup allows my Victron Orion-Tr DC-DC charger to work like a champ.

 

@B-ManFX4 Is that the 30Amp charger?

Also, I think the largest cable that will fit in the Victron charger is 6AWG. How did you manage that?

 

My Orion is 15 amps because it is charging a 24 volt battery bank, but that is the output side. It is a 360 watt unit so yes, it would pull roughly 30 amps from the truck if outputting its full rated output into the battery bank. The Orion is installed in my RV. The RV-side connector for the truck power goes to my "power board" in the pass-through. The 1/0 goes to a fuse and from there it is wired into the Orion with 6AWG. So overall it is 1/0 from the truck battery to the RV power board. To be totally honest I have not put a meter on the Orion input to see what the exact input voltage is but the Victron app tells me its over 13.8 VDC input voltage with the truck running. The batteries charge on our longer drives so I am happy with how it performs. I am considering increasing my RV battery bank size. If I do that I will add another Orion into the mix. Once it warms up I plan on doing a battery test and I will measure the voltages at the Orion to see what is happening with a higher-current load on it. It sure would be nice if we had some idea of what the alternator states are in the truck. It seems like both running at 50% capacity or whatever would be better than one running at 100% before the other is switched on.

 

When I did this back in 2020, I ran 2 gauge back to the rear of the truck and 6 gauge to my 30 amp Victron charger. The 6 gauge run was less than 10 feet, so I wasn't worried about voltage drop.

 

One thing to be careful of when installing a DC-DC charger is where it is in the circuit. A DC-DC charger is one-way power. It only flows toward the battery to be charged. If you install it in the wrong spot, your trailer breakaway system will not have power when the 7-pin cable is disconnected.