I've been researching this - and found bits of info. My goal is to use a Renogy DCC50S mounted on my Travel Trailer (TT) to charge my batteries from Solar and Tow Vehicle (TV) alternator. This unit can DC DC charge TT batteries at 25A from the TV. It also charges TT batteries from solar at 25A. There is also a smaller version (DCC30S) that only DC DC charges at 15A - but I would prefer the 25A option.

I believe my 2020 f150 has 30A fused power through the 7-pin connector. I have read different reviews of the parasitic losses on the f150 (any truck really) due to thin wire running to the 7-pin connector. I would rather not add a second connector from TV to TT just for the power to drive the DC DC charger - which I have read about in other posts. Given that the truck is fused at 30A, I would rather upgrade the existing wire that runs from fuse box (I assume) to the 7-pin to better support the full 30A current. By going to a 4 gauge wire, my hope is that there is minimal parasitic loss over the run, and therefore I can still use just the 7-pin connector. To be clear, I would also upgrade the wire on the TT side of the plug.

Has anybody done this?

 

I think I have heard that the voltage at the 7-way is "ONE WAY" from truck to the 7 way.. I believe that it has a diode to do this. You would have to remove that 'protection' device to do what you want to do unless you run a separate wire from the RV solar to the truck battery.

 

There are better DC-DC chargers out there. The Victron line of DC-DC chargers have automatic sensing to detect when the engine is running (higher voltage from the alternator).

The Renogy DC-DC/MPPT is, in my not so humble opinion, crap. The maximum PV input voltage is limited to 25 volts. You have to put in a fairly small/weak solar panel to keep under 25 volts. Should you ever upgrade/increase the solar panels on your trailer, the Renogy unit will have to go. Renogy quality hasn't been very good lately. I'm reading about quite a few problems with their MPPT devices.

I do not use the 7-pin circuit to charge the house batteries (LiFePO4) in my travel trailer. I chose to disconnect the 7-pin circuit from the house batteries. They are now charged only by solar and the very infrequent use of shore power/generator. If I did want some charge to the LiFePO4 battery bank from the tow vehicle, I would use the 7-pin circuit and choose a DC-DC charger with an output of less than 20 amps.

I think that adding a new wire to the bumper, instead of replacing the existing wire, would be easier.

 

Our truck camper is fitted with solar modules and a Victron MPPT charge controller with the option battery sense module. Our Ford’s trailer wiring “smart controller” is a tad underwhelming, IMHO, so, I’m considering adding a DC-DC charger to help run the three-way fridge and correctly charge the house batteries while driving. The overall architecture should improve electrical performance while boondocking.

My current thinking is to disconnect the +12 circuit at the input circuit breaker in the camper and use one of the two 40 A upfitter switches to power a separate harness into to the DC-DC charger in the camper, and perhaps from the charger to the same CB as a landing point. The new harness will likely use Anderson connectors (with weather boots?) and also contain a separate common circuit.

I hope to install our WeBoost cell booster later this month, and we have a trip scheduled to begin in early May, so it may be June before I can tackle this project.

HTH,
Jim / crewzer

 

Here's what I was wondering about the DC-DC charger since my interest has increased. Since it only is activate with the engine running are folks driving around often enough to make it a viable alternative system or do they idle their engines while camping, which seems to me to not be ideal?

Steve

 

Steve,

My take on the Victron DC-DC battery charger is that it has two primary strategies. One is to overcome the voltage loss in the tow vehicle’s trailer battery charging circuit.

For example, assuming 87% efficiency, 12 V x 20 A in would be converted to 14.4 V X 14.5 A out.

The other strategy is to provide a smart charging algorithm to the charger’s output in order to correctly charge the house batteries, especially if the charger includes sensing for battery terminal voltage and battery temperature.

In short, I see the goal is to correctly charge the house batteries while underway and arrive at a camp site with fully charged batteries. Once the tow vehicle’s engine is shut down, then the DC-DC charger will isolate the house batteries from the chassis battery and essentially go to sleep.

It’s possible that a drive between two campsites won’t be long enough to fully recharge the house batteries. In our case, it’ll be the PV system’s job to complete that task. However, I will have been able to run the three-way fridge from DC (my preference) while charging the batteries from the truck, and, on a clear day, from the PV system as well.

HTH,
Jim / crewzer

 

The third strategy (use case) for a DC-DC charger is appropriate only for Lithium type batteries. The low resistance of the battery can - if you believe what you see on YouBoob - burn out an alternator. This situation would occur if the LiFePO4 battery bank was at a low state of charge. It has the potential to suck up every possible amp from the alternator.

I'm not 100%convinced that would happen, at least maybe not on our Superduty trucks with the dual alternators. That said, it's enough of a possibility that I would want something between my alternator and my LiFePO4 battery to throttle the number of amps coming out of the alternator.

 

The Anderson weather boots work really well. They've done a good job of keeping the connectors clean and dry both when connected as well as stored. Below are some pics of my second umbilical with the Anderson connectors for my Victron Orion-TR Smart 12-12/30 unit. So far I'm quite pleased with how the unit is working. I did create a custom charge profile on the Orion-TR for my Trojan T-125 GC2's using the details from the Trojan data sheet.

 

ttavasc,

Thanks for your comments on the weather boots. I like that the “source” and “load” variants are designed to seal together.

The Victron Orion-tr Smart 12-12/30 (non-isolated) DC-DC charger is exactly the model I have in mind for my project. The 30 A output should be plenty to run our three-way fridge on DC (~18 A) plus charge the house batteries.

https://www.victronenergy.com/dc-dc-...t-non-isolated

Custom charge profiles based on manufacturer recommendations are definitively the way to go.

A couple of questions, if I may:

1) What’s the +12 source point for your custom harness? I’m considering using one of our truck’s 40 A upfitter switches.

2) What wire gauge did you use for your harness? My harness will likely be ~18’ (each way; upfitter switch to charger in camper and back), so I’m thinking high-temp 6 AWG will work satisfactorily.

Thanks, and safe travels!
Jim / crewzer

 

The Load/Source pairing of the environmental boots is definitely a nice feature and so far after towing in some heavy rains they seem to be doing a good job of keeping the connectors dry. Unfortunately I missed the fact that "Load" and "Source" are printed on the covers. As you can see I ended up with "Load" on the truck side and it should have been "Source".......

I'm using the Isolated version of the Orion-TR and I went rather old-school on the truck harness. I simply wired from the + of the battery through a Blue Sea CB to a Cole-Hersee 85a continuous duty solenoid. I tapped into an ignition-switched fuse so that the solenoid is only active when the key is on. While the Orion-TR does have ignition-sensing capability from what I've seen it can be a bit fickle and takes some work to get fine-tuned based on details I've seen posted by someone who got it working. The solenoid avoids all that as would using an upfitter switch. From there I followed the main wiring harnesses that are run down the drivers side to the rear where I "creatively" mounted the Anderson connector to the hitch frame with a couple of large hose clamps and a small metal handle. I used Temco 2AWG welding cable for the truck side of things and Temco 6AWG welding cable for the trailer side as that is the largest wire that fits the Orion-TR lugs. All wire runs are also encapsulated in high-heat split wire loom for added protection. I think I ended up using ~26-27 feet of the 2AWG for the positive run - the negative was much shorter since it just went from the Anderson to ground on the hitch frame. Below are a few more photos of the truck side of things. There is also a screenshot of the Victron Connect app showing the current from the Orion-TR as we headed out from an overnight at a rest area last fall.

 

Thanks for the additional details and pics!

Safe travels,
Jim / crewzer

 

@ttavasc , nice install. Looks like it was a PITA to get that solenoid back behind the fuse box.

 

It did take a bit of maneuvering to get it positioned just right so that I can still get the cover off the fuse box. I used a combination drill and tap bit with some cutting oil as I'd heard drilling into the firewall could be a bit of a chore. Here's a better shot showing the placement tucked up behind the heat shield on the back of the fuse box. This was the only place I could find that allowed for a short wire run from the battery to the CB to the solenoid and be reasonably close to the fuse box to tap into the ignition-switched fuse.

 

Thanks for the additional picture. That makes it look not so bad. I opened my fuse box today. It was almost impossible to open without removing the huge wire harness on the driver side of the fuse box. In your picture, the fuse box isn't so crowded. I wonder if that's due to the 6.2L engine instead of my 6.7L. In fact, your harness isn't the same.

 

This might be a case where getting the engine detection feature working would be easier than the solenoid route. I found the post on the RV forum where the user provided some details on getting the engine detection feature working and am pasting them in below for anyone who is interested. They were configuring the Orion-TR Smart 12/12-18 model but should also apply to the 12/12-30 as well: