DC/DC charger installation advice

**putzpilot** · 09-15-2021, 11:41 PM

Hey there folks, although I'm a fairly experienced RV'er I am new to the Grand RV forum. I took delivery of my 2021 310GK/R in July and am now in the process of "moving in" and making the desired adjustments and upgrades to prepare for the upcoming Snowbird season. I have the factory 300 watt solar system and have added one additional 100 watt panel. I have three Renogy 12v 100 amp Lithium batteries and have replaced the original deck mounted charger with the Lithium compatible WFCO unit. I now realize that it will be advantageous to also install a DC/DC charger so that I can get a better charge to the battery bank while on the road. I will be using a Renogy 20 amp DC/DC charger unit. My tow vehicle is a 2016 Silverado 2500HD Duramax diesel.

I am asking for direction regarding the best/proper place to draw power for the new charger. In other words where do I find the 12 volt+ wire (coming from the pigtail junction box near the kingpin) in the forward equipment/battery bay? And... where can I best access the marker light power feed wire from the same junction box? I will splice into that wire for the D+ connection to the charger so that the unit will only power up when the marker lights are on.

Any guidance from another 310GK owner would be greatly appreciated. The forward compartment is such a tangled mess of wires and cables I am not sure where to start in trying to locate the two needed wires. My many thanks in advance.....

Putz Pilot.

**gbkims** · 09-16-2021, 07:54 AM

Originally Posted by putzpilot

Hey there folks, although I'm a fairly experienced RV'er...I now realize that it will be advantageous to also install a DC/DC charger so that I can get a better charge to the battery bank while on the road. I will be using a Renogy 20 amp DC/DC charger unit. My tow vehicle is a 2016 Silverado 2500HD Duramax diesel.

I am asking for direction regarding the best/proper place to draw power for the new charger. In other words where do I find the 12 volt+ wire (coming from the pigtail junction box near the kingpin) in the forward equipment/battery bay? And... where can I best access the marker light power feed wire from the same junction box? I will splice into that wire for the D+ connection to the charger so that the unit will only power up when the marker lights are on.
...The forward compartment is such a tangled mess of wires and cables I am not sure where to start in trying to locate the two needed wires. My many thanks in advance.....

Putz Pilot.

+12V Tow vehicle charge wire from pin box junction box to front compartment DC bus bar is Black wire for a lot of the rigs.
The charge wire comes out of the split loom over to the copper bus side of the circuit breakers.
Might be similar to. May give you a start on finding it.

Click image for larger version.

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I think the Marker light wire(mine's Green) from the pin box junction box to front compartment (in split loom) runs straight thru front compartment to underbelly.

Another fellow on a different website has a 2015 GMC Sierra and runs his 20A Renogy from the charge wire.

Attached my pin box diagram, it has some different wire colors than new rigs.

Click image for larger version.

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**Butcher** · 09-16-2021, 10:22 AM

I suspect there is no power wire large enough and you will have to route your own from the battery to the DC/DC charger. I would think a 2 AWG wire or larger would be needed. A quick disconnect [Andersen plug?] would also be used. The ground cable may be slightly small in gauge since it would be a much shorter run.

From my understanding, it may charge the lithium battery at 20A but it will need more to make that happen. Of course, reading the owners manual and calling Renogy would be the first place I would be looking at for information to do it right.

Don't forget you'll need a good fuse/circuit breaker if you are going to run a cable that long.

**wjpatter** · 09-16-2021, 11:23 AM

Originally Posted by putzpilot

Hey there folks, although I'm a fairly experienced RV'er I am new to the Grand RV forum. I took delivery of my 2021 310GK/R in July and am now in the process of "moving in" and making the desired adjustments and upgrades to prepare for the upcoming Snowbird season. I have the factory 300 watt solar system and have added one additional 100 watt panel. I have three Renogy 12v 100 amp Lithium batteries and have replaced the original deck mounted charger with the Lithium compatible WFCO unit. I now realize that it will be advantageous to also install a DC/DC charger so that I can get a better charge to the battery bank while on the road. I will be using a Renogy 20 amp DC/DC charger unit. My tow vehicle is a 2016 Silverado 2500HD Duramax diesel.

I am asking for direction regarding the best/proper place to draw power for the new charger. In other words where do I find the 12 volt+ wire (coming from the pigtail junction box near the kingpin) in the forward equipment/battery bay? And... where can I best access the marker light power feed wire from the same junction box? I will splice into that wire for the D+ connection to the charger so that the unit will only power up when the marker lights are on.

Any guidance from another 310GK owner would be greatly appreciated. The forward compartment is such a tangled mess of wires and cables I am not sure where to start in trying to locate the two needed wires. My many thanks in advance.....

Putz Pilot.

If you haven't bought the DC-DC charger, I would recommend upgrading to the 50amp model. It was the best single change that I made to the unit. I did have to run 4 gauge wires from the truck battery to the bed. The details for the mod are at this link. The second modification was to isolate the external refrigerator and run off the inverter while I travels. It turns out that both refrigerators were on the same line and I got two for one. Both refrigerator and battery charger typically sucked 45 amps from the vehicle.

https://www.mygrandrv.com/forum/show...ghlight=renogy

**Dnmatt** · 09-16-2021, 07:44 PM

Originally Posted by wjpatter

If you haven't bought the DC-DC charger, I would recommend upgrading to the 50amp model. It was the best single change that I made to the unit. I did have to run 4 gauge wires from the truck battery to the bed. The details for the mod are at this link. The second modification was to isolate the external refrigerator and run off the inverter while I travels. It turns out that both refrigerators were on the same line and I got two for one. Both refrigerator and battery charger typically sucked 45 amps from the vehicle.

https://www.mygrandrv.com/forum/show...ghlight=renogy

This is what I did also. Ran 4 gauge with a 85 amp circuit breaker right at the battery. I actually got the combo 50 DC-DC converter and solar controller from Renogy. My trailer didn't have solar so I added 2 panels with the Renogy controller.

For me when running the wire from the battery, I added an Anderson 120A connector with a weather boot on the truck and the trailer. Makes a great clean connection.

**SolarPoweredRV** · 09-16-2021, 10:57 PM

Originally Posted by Dnmatt

This is what I did also. Ran 4 gauge with a 85 amp circuit breaker right at the battery. I actually got the combo 50 DC-DC converter and solar controller from Renogy. My trailer didn't have solar so I added 2 panels with the Renogy controller.

For me when running the wire from the battery, I added an Anderson 120A connector with a weather boot on the truck and the trailer. Makes a great clean connection.

This sounds like the best installation approach.

As far as controlling the DC/DC Charger goes, you could tap into an Upfitter Switch (if you have that option) or tap into the marker lights on the truck (personally, I would install a dedicated switch to control the DC/DC Charger inside the cab).

**putzpilot** · 09-25-2021, 10:30 AM

Gene, many thanks for your response and especially the picture. Also my apologies for this delayed note. Your info and picture are just what I had hoped to see. I now know just where the wire bundle is located and should have no issue in setting up my DC-DC charger. My unit is in at Blue Dog RV getting the post delivery shake-down-cruise warranty items taken care of. As soon as I get her back I'll be installing the charger.

There have been other... "interesting" responses, some with good thoughts and some that (although appreciated) I felt were going overboard. My intent is to have a system that will slow-charge the batteries while under tow when there is inadequate solar charge being produced. I don't need to have the truck supplying 50 plus amps for a rapid charge of the batteries. Since the DC-DC charger will normally only be in use while on the road (and since that will generally be for a minimum of a few hours at a time) 20 amps is plenty. The power feed in the truck 7-way is fused at 30 amps and I will continue with the remainder of the wiring sized accordingly. I will use 8awg wiring and place 30 amp fuses on both the input and output from the charger. While a separate, switched, power source for the D+ lead would be preferred I am way to lazy to run that from the truck cab back to the trailer. Splicing into the marker light power is quick and easy, and provide adequate control of the charger. I believe I read the other article you mentioned and this setup seemed to be working just fine for that fellow. I am confidant it will serve my needs as well.

Once again my many thanks.

**Butcher** · 09-26-2021, 08:57 AM

I really think you should take your thoughts to a professional because 8awg will not provide that kind of current for that distance. I believe your thoughts do not jive with the facts about electricity.

**Dnmatt** · 09-26-2021, 04:35 PM

Originally Posted by Butcher

I really think you should take your thoughts to a professional because 8awg will not provide that kind of current for that distance. I believe your thoughts do not jive with the facts about electricity.

Agree 100%. Also remember that there will be times solar just won't provide enough to charge the batteries and the only option would be from the truck.

PS, I'm not a professional but am an electrical engineer and understand this stuff quite a lot.

**timkoenig** · 09-26-2021, 08:31 PM

I am running a 20 amp DC DC charger off the factory Ford trailer power output. I just wired it in series in the front compartment of the rig. I think it pulls a little less than 20 amps from the truck and Ford has a 30 amp fuse in that circuit. The BMS shows about 13 amps going into the battery of course that is up close to 14 volts. So if you do the math I think I am losing 2-3 volts to the wiring from alternator to charger. I guess I should measure that but it works.