DC to DC charger for RV batteries.

I have a travel trailer that has an off-grid 12v lithium battery system, it has 960ah of capacity so it's a decent size.

Charging the system via solar/generator can be a chore at times depend on the condition, so now I'm looking for DC to DC charging when towing, has anyone done something like this on a Tundra?

 

What kind of trailer? Most trailers come equipped to charge the house battery off the 7-pin while the truck is running…

 

this one is just a Winnebago Voyage, but we (mostly the shop) had been building full electrical system, the 7pin only charges at about 2-3 amps, the solar controller charges at best 25amp (it's a 30amp solar controller and only 400w of solar), the whole system can charge at up to 100amp safely, as we are running everything Victron, so with that being said.

If I can do DC-DC from the truck while towing at say 20amp, that'll double my charging while towing/traveling, cause even running a generator at best I'm running 20amp of output.

Trailer side, that's all sorted, but I'm trying to figure out the truck side on how to do this.

 

$63 Dual Battery Isolator Kit - 12 Volt 140 Amp Voltage Sensitive Relay - Complete VSR Double Battery Automatic Charger - Fits Trucks, ATV, SUV, UTV Boats and More - Safe, Water and Vibration Resistant

https://www.amazon.com/gp/product/B07N15Z5GP

 

I have my DC/DC installed on the camper side, but I need to install the wire along the truck. It’s a pretty staightforward install. 6 gauge copper, fuse near the truck battery, and I’ll do a quick connector near the rear license plate somewhere. One of those winch style male/female connectors. Victron makes nice DC/DC chargers, they outline the wire sizing and fuse needs. They are not cheap, but they draw power from the truck battery so I don’t want to mess that up.

 

It's "up to", not "always". Truck's charging system generates little current if battery is full.

 

Your isolator suggestion made so much more sense I just deleted my post!

 

Alternator + ECU will do just the same thing even without isolator. When the battery is charged, it makes no sense punishing it with hundred+ amps, so ECU commands voltage regulator in alternator to generate less amps.

 

Absolutely - I guess my concern would be making sure your trailer batteries are still getting juice even when your truck battery is topped off.

I’d think the 7pin amperage doesn’t drop even when the truck battery is happy. FWIW, I altered my 12v air compressor to run off the 7 pin aux and have never had any issue. I’d certainly think it uses more than 2 amps… the 7 pin is on a 40amp fuse.

 

As others stated, I would run a thick dedicated 12v wire directly from the starting battery instead of tapping into the 7-pin system in any way, and add an Anderson connector to disconnect that wire from the trailer. Unless you don't have room in the trailer or absolutely need it in the truck, I'd probably try to put the charger in the trailer.

 

Isolator does not cut if the voltage is above 13.8V (IIRC). On-board electric system voltage is above that, in a close vicinity to the battery, where isolator should be placed. Alternator will "see" both batteries and will keep charging until both batteries are level.

Nice thing is that isolator has a pass-through mode than can be enabled to start the engine with the secondary battery when the main one died. Or when you winch hard and need all hands on deck.

 

Just get something like the renogy dc-dc charger and run a big power wire back to the trailer with a plug at the hitch, like @des2mtn said. the charger will only run when it senses the truck is running (or control it with a switch if you want) so it acts as an isolator so you can't run down the truck battery when the engine is off.

 

I second @helidave comment about a renogy. I love mine and have the original version. The newer versions of the mppt dc-dc are even better. You can hook your solar up to the dc-dc and it will reverse trickle charge your starting battery once your house battery is full (I have tested this when I drained my starting battery once). Redarcs are very similar but cut out after 2 hours of charging. Sorry for the crappy response but crazy day at work. Will respond tonight (if I remember) with a more thorough response. And don’t do an isolator switch unless the battery chemistry is identical between the starter and house bank, can lead to problems. That’s why they have dc-dc’s

 

Thank you guys for the input, made lot more sense than the scenarios I have running in my head.

That made a lot of sense, thank you sir.

we planning to run anderson connector, it'll be installed next to the 7 pins, but yes , the whole trailer is Victron, the inverter is a multiplus ii, running the lynx distributors, and the cerbo gx, I've taken what I've learned with the previous trailer and making this one right.

7 pin amperage stays constant, that one we've tested and figure out, when I had Xantrex inverter, it would not charge above 2 amps with truck running.

Got lots of room in the trailer, now I'm debating to switch to Antigraviy lithium trailer for the truck too, they have internal BMS which can stabilize the draw

I go the new Victron DC to DC charger ,I need to read up the instruction on settings, this is the one we are running:
https://www.victronenergy.com/dc-dc-converters/orion-xs-12-12-50a-dc-dc-battery-charger

 

One point of curiosity is what are you doing with 960ah in a mobile setting? A lot of people don’t even have something that big at their house..

 

Victron DC-DC charger (and appropriate GA cable run to support it) would certainly be an effective means of charging while traveling, but if you have the real estate you might wanna' consider adding more solar.

My understanding is that the general rule of thumb is to have 200W of panels for every 100Ah of battery.

400W of solar feeding a 960Ah battery bank is asking it to breathe through a straw.

If you can add more panels you still get the charging benefits while traveling as you would with the DC-DC, but you also get it while sitting in the campsite or any other time the sun's out which the DC-DC does not provide. (Unless you wanna' sit there with truck running)

Now mind you, I've only got 200Ah of lithium, but the 600W of panels always has me back at 100% SOC by noon.

Gotta' love it, power is now one less thing I ever have to worry about.

 

Running the air conditioning would be my guess.

 

Anderson connector, that’s what they’re called, thanks!

I also went with Victron this time around but there’s a lot of good makers out there. This time I made a long/narrow cage so I could maximize space in my front camper compartment and also have a shelf on top of my batteries. Also I can remove the install in one piece. I also went with heated batteries this time around since they are in the front compartment of the camper.

 

if OP is camping in treed areas, solar is pretty much useless.

 

Obviously.

I made the assumption was that since OP bothered to put 400W of solar on the rig in the first place, that it must be a viable option.

 

Still seems like a lot given my cursory review of A/C current draw.. unless you’re running is day and night and not just to sleep.

Same could be said about a dc-dc. Most people would just hook up a generator instead of having their truck idle for hours. Less fuel and no wear/tear on the truck. I agree with @SD Surfer more panels if there is the real estate. Why not, they’re dirt cheap.

 

If you have a soft start for the A/C, it shouldn't draw as much power on startup and it also shouldn't cycle as much.

 

Like other mentioned, A/C and the way we camp, it becomes more or less a traveling cottage, we originally bought a Winnebago Micro Minnie FLX, it came with 1x 320ah battery, we thought we would've done all the cool glamping like out of boonies stuff, turns out we didn't, instead we camp often for 3-5 days at once, quickly we learned 320ah is not really enough, even when sun was out, the a/c can only be run for about 2hrs and it'll consume 45-50% of the charge.

At 640ah, it was decent, but last trip we had in the summer, we almost ran out of juice by day 6, the trailer had 190w of solar and we had good sun for about 10hrs a day.

I envy you with the sun, most camp grounds with spots available are in the forests.



New trailer has 200w stock, I added another set with existing mounts, I'm trying to avoid drilling into the top, drilling on top in Canada is just not that good of an idea, they will always leak.

I like this, this is proper! old trailer had Xantrex inverter, it was good but not that good, and costs 2x of Victron, I had close call of fires with shoddy factory wirings, so this time I'm trying to keep 'em one manufacturer.

Yes, adding soft start as well, I'm going to try to add tint, not sure if it'll work but only one way to find out.

 

I'd love to do more forest camping... living in San Diego I have a lot more desert available and close than I do forests.





Looks like we have the same zero gravity chairs!

 

hell yea on those gravity chairs, bought ours from Princess Auto, it's Canadian version of Harbor freight, has some of the best naps on those things.

Forest is awesome for environment, you feel very safe even during crappy weather, but the bugs......... every time I travel to South West, I envy you guys with lack of bugs, mosquitoes and deer/black flies in Canada can be overwhelming if you are not familiar with it.

 

I also love that they put my tootsies at just the right height for warming near the fire bowl.

A lot of times sitting by regular campsite fire rings my face is melting while my toes are cold.

With the propane fire bowl, I miss the ritualistic fun of building, stoking, playing with wood fire, but I can keep my little piggies quite happy.

 

HA, I have same firebowl, wood fire smells great but getting one started is a pain.

We also had a brown dog, this is Bear ,this was his last camping trip, he had a beautiful long life for 17.5 years, he was one of the main reason we got a trailer.

 

Bear! What a good boy! 17.5 is amazing for a big dog.

Riley was 14 when he got called home.



His duties of "Chief Knucklehead" are now being handled by Diego and Sadie, and supervised by Quincy the cranky old man.

So much nicer camping with dogs, which is weird 'cuz they're really kind of a pain in the ass!













Sadly, I can't have Quincy spell me on the street 'cuz of his road rage, but he does pretty good in the dirt.

 

As much as I like Victron, their DC to DC units get pretty hot and need to be mounted vertical to allow for convection cooling. They also reduce charge current when hot.

I'm a big fan of the Redarc BCDC chargers. Since the 2nd gen lacks a smart alternator, wiring is incredibly simple. Just run the appropriate size wire to the starting battery and that's it. The BCDC detects the increased voltage and starts charging.