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Before I go over my setup, I did this mod to get correct charge voltage to my trailer’s lithium batteries, not to maximize charging from my truck’s alternators.
For my Momentum 23G I have two GC2 pattern 100 Ah Battleborn batteries, with the factory 300w Jaboni solar system and a WFCO WF-8950L2-MBA Lithium Power Converter installed. So everything is lithium compatible except for charging through the 7 way connector when towing. Through that connection my truck puts out about 8-9 amps as measured by the Victron Shunt on the trailer. The problem is when the truck’s smart alternators (I have dual alternators, 6.7L diesel 2019 F250) decide to drop voltage to ~13.6 volts, amperage to the trailer batteries drops to zero no matter how full the lithium batteries are. For example, on my last drive back from camping the batteries were at about 80%, but were not taking a charge from the truck because the alternators were putting out less than 14 volts.
To solve this I looked at DC-DC chargers to install on the power wire of the 7 way plug. Since I know the power wire on the 7 way plug is 12-10 gauge at best on the truck and trailer, and is about 20 feet in total length, I wanted a DC-DC charger that put out no more than 10 amps to not overload that line. I settled on the Renogy 20amp charger using the 10amp current limit option. I located a place to install it on the frame underneath the front cap and used 10 gauge wire to tap into the 7 way junction box on the trailer. I replaced the wire nut and electrical tape on the positive wire with a 10 gauge butt connector, and replaced the ground wire to the 5-way wago connection inside the junction box with a 10 gauge stranded wire with an eyelet connector rather than the hard green wire wrapped around the negative ground on the junction box. I did this so I could run the DC-DC Charger ground wire to that same ground point also using an eyelet connector. Hopefully you can see all this in the pictures so it makes more sense.
Everything works as planned and I now get 10 amps to the trailer all the way until the batteries are full, and only then does it drop off when the batteries are over 99%. I did have one issue though. When I first plugged in the 7 way and started the truck I did not get any power. The DC-DC charger light was green, just no power output. After taking a break and coming back the next day, it turns out when I installed the charger I accidentally bumped the dip switches and messed up the charge parameters. Once I set them correctly everything worked as expected! Attached are the before and after pictures.
There is so much confusing information online on what the 7 way plug can and cannot support power output wise, so I wanted to share my setup in case this helps anyone. Not all tow vehicles are the same, so the above may only work for newer Ford Super Duty trucks.
For my Momentum 23G I have two GC2 pattern 100 Ah Battleborn batteries, with the factory 300w Jaboni solar system and a WFCO WF-8950L2-MBA Lithium Power Converter installed. So everything is lithium compatible except for charging through the 7 way connector when towing. Through that connection my truck puts out about 8-9 amps as measured by the Victron Shunt on the trailer. The problem is when the truck’s smart alternators (I have dual alternators, 6.7L diesel 2019 F250) decide to drop voltage to ~13.6 volts, amperage to the trailer batteries drops to zero no matter how full the lithium batteries are. For example, on my last drive back from camping the batteries were at about 80%, but were not taking a charge from the truck because the alternators were putting out less than 14 volts.
To solve this I looked at DC-DC chargers to install on the power wire of the 7 way plug. Since I know the power wire on the 7 way plug is 12-10 gauge at best on the truck and trailer, and is about 20 feet in total length, I wanted a DC-DC charger that put out no more than 10 amps to not overload that line. I settled on the Renogy 20amp charger using the 10amp current limit option. I located a place to install it on the frame underneath the front cap and used 10 gauge wire to tap into the 7 way junction box on the trailer. I replaced the wire nut and electrical tape on the positive wire with a 10 gauge butt connector, and replaced the ground wire to the 5-way wago connection inside the junction box with a 10 gauge stranded wire with an eyelet connector rather than the hard green wire wrapped around the negative ground on the junction box. I did this so I could run the DC-DC Charger ground wire to that same ground point also using an eyelet connector. Hopefully you can see all this in the pictures so it makes more sense.
Everything works as planned and I now get 10 amps to the trailer all the way until the batteries are full, and only then does it drop off when the batteries are over 99%. I did have one issue though. When I first plugged in the 7 way and started the truck I did not get any power. The DC-DC charger light was green, just no power output. After taking a break and coming back the next day, it turns out when I installed the charger I accidentally bumped the dip switches and messed up the charge parameters. Once I set them correctly everything worked as expected! Attached are the before and after pictures.
There is so much confusing information online on what the 7 way plug can and cannot support power output wise, so I wanted to share my setup in case this helps anyone. Not all tow vehicles are the same, so the above may only work for newer Ford Super Duty trucks.
Attached Files
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