Help me Understand DC to DC charging

[TechnoRoamer]

@Thedantons
There has been a lot of great info on this so far. Something that I see missing is the size of the Dakota Lithium batteries and how many AH you are trying to supplement? Are they both 100ah for a total of 200ah or is it higher? This could definitely impact the size of the DC to DC you get. Especially if you plan to add any more batteries.

You also mentioned having the 12v fridge, the DC to DC will basically power this while driving thus not putting all 18amps (if thats the size you go with) into the batteries. Depending on how many hours you drive/tow and how often you use the trailer and the weather you are in will impact your choices here.

18amp if you use it for weekends only.

Would recommend a larger DC to DC if you use the trailer more or for longer trips. As others have mentioned this would require a new wire being run but this is actually really simple. Nothing needs to be done with the 7pin if you do this as well.

We have taken our trailer out for months at a time, we have 600w of solar and 400ah of battery. This year while going from AZ to FL we were in the rain almost every day. The solar did help but it was only pushing 50-150w for a number of days. I have now added a 30amp Victron Orion (smart and isolated) to the mix and it makes all the difference. Keeps things charged and runs the fridge without any issues. Once we hit FL we were also producing 500+ watts from solar so things charged really fast.

[thedantons]

Originally Posted by TechnoRoamer

@Thedantons
There has been a lot of great info on this so far. Something that I see missing is the size of the Dakota Lithium batteries and how many AH you are trying to supplement? Are they both 100ah for a total of 200ah or is it higher? This could definitely impact the size of the DC to DC you get. Especially if you plan to add any more batteries.

You also mentioned having the 12v fridge, the DC to DC will basically power this while driving thus not putting all 18amps (if thats the size you go with) into the batteries. Depending on how many hours you drive/tow and how often you use the trailer and the weather you are in will impact your choices here.

18amp if you use it for weekends only.

Would recommend a larger DC to DC if you use the trailer more or for longer trips. As others have mentioned this would require a new wire being run but this is actually really simple. Nothing needs to be done with the 7pin if you do this as well.

We have taken our trailer out for months at a time, we have 600w of solar and 400ah of battery. This year while going from AZ to FL we were in the rain almost every day. The solar did help but it was only pushing 50-150w for a number of days. I have now added a 30amp Victron Orion (smart and isolated) to the mix and it makes all the difference. Keeps things charged and runs the fridge without any issues. Once we hit FL we were also producing 500+ watts from solar so things charged really fast.

I have to be honest. I can’t remember but I keep thinking they are 135 ah lithium batteries so 270 ah total. We mostly are weekend worriers. We may plan a week long trim every once in a while.

Again, Thanks for all of this wonderful information.

[pboomerx]

The classic 7 pin connector has a 12V line that has been used for charging the trailer battery and/or powering the trailer. Several recent changes have caused this to become inadequate. First, trailers have become much more power hungry and require more power to run all the gadgets inside them. Second, lithium batteries being installed in trailers can draw significant power during recharge as well as having a different charge profile than the lead acid batteries in the tow vehicle. Third, modern vehicles often have variable voltage charging systems that are designed for charging the tow vehicle efficiently, not necessarily the trailer.

The DC-to-DC converter is effectively a buffer between the battery/charging system of the tow vehicle and the trailer. It can be programmed to charge the trailer at the proper charge profile. It can provide the proper voltage for charging irrespective of the trailer's alternator voltage setting. And it can provide sufficient current to charge the trailer's battery bank within a reasonable time period, irrespective of other charging facilities, such as solar.

The two main caveats are the need for wiring to support the current load and a alternator system that can provide sufficient current without damage.

For example, in my GMC 2500HD, I have 6 gauge wire running from the battery directly to the back bumper where Anderson connectors connect to the trailer. The DC-to-DC convertor is in the battery box of my Airstream. In the battery box is a Redarc 40A DC-to-DC converter. The truck has two alternators capable of over 400A of current. There are two 100A Battleborn lithium batteries in the battery box as well.

I never arrive at camp with nothing less than full charge, irrespective of weather.

[ricjones]

Originally Posted by thedantons

Than you all for this information. I guess more information would be needed. When I purchased the camper they had just installed two new Dakota Lithium batteries. It does have solar and I am running a 12v fridge.

The batteries are not charging to 100% on shore power. ( I have identified I need to upgrade my converter to WF-8955-AD-MBA or something similar.)

the other question was the DC to Dc charging. Since all this electrical stuff is new to me, I am not sure what I even need to look at. I have a Victron MPPT 75/15 and a 712 BMV. So, I was looking at the Victron Orion, but not sure which one I would need.

I also did not know if I needed to run a new wire to the battery or if I wired off of the 7 pin inside the camper.

I hope my rambling is not too bad. Thanks again

FYI in this part/model/serial number:
WF-8955-AD-MBA
the "AD" means "Auto Detect" meaning it detects your battery type and charges for that battery. We have an AD in our 2022 and it worked with AGMs and charges to 100% with our Lithiums.

[ricjones]

We have not upgraded to a DC DC charger but plan to. In the meantime a fact we learned is that our 270 watts of roof solar keeps the batteries charged IF THERE IS SUN SHINING .

In full sun we get 10-12 Amps Per Hour.
In partly sunny skies we get 5-7 Amps Per Hour.
Even in total clouds and under trees we get an 1 - 1.5 Amps per hour.

But the bigger issue is that sometimes, the battery management system (BMS) in our batteries, does not turn the solar charging onto bulk (full charging) mode sometimes.

Our trick is that if we hit the battery disconnect button (a glowing green light button in newer AS's), it resets something (likely the BMS) and the solar comes it at full amperage in bulk mode.

This helps a lot and 270 watts with decent sun keeps our 200AmpHr Lithiums charged.

The 12V fridge we love. It worked far better than any fridge in our past 4 Airstreams whether propane or electric modes and it is worth the watts. It is never not cold. Before we worried about the fridge. Probably unnecessarily but we did.

The new 12V fridge seems to use about 3A per our when running. But it seems to vary somewhat. Also, there are no side vents anymore, just a roof vent.

[uncle_bob]

Hi

We have headed out for 6+ months with our rig in multiple years. The DC/DC runs on the 7 pin. There's nothing fancy about its hookup. On a 5 hour drive, ~18A of charging gets you 90AH into the battery. If your solar is delivering 100W average that's another 40 AH. Unless you *use* more than 130AH a day (and we don't come close to that), you can drive for days, weeks, months and not have any problems with the battery bank.

Bob

[kmrice]

Originally Posted by uncle_bob

Hi
Hookup wise, 12V wire from the 7 pin comes off the DC bus bar. That wire goes to the input on the Orion. Wire from the output of the Orion goes to the bus bar. Negatives both go to the ground bus bar.

Bob

I have another one of my usual pretty ignorant questions: where would the DC bus bar be? Is that on the fuse panel? This would be on a 2022 Globetrotter 23 FB Twin.

Any guidance would be greatly appreciated.

Thanks, as always,

Karl

[uncle_bob]

Originally Posted by kmrice

I have another one of my usual pretty ignorant questions: where would the DC bus bar be? Is that on the fuse panel? This would be on a 2022 Globetrotter 23 FB Twin.

Any guidance would be greatly appreciated.

Thanks, as always,

Karl

Hi

One of the fun parts of owning an RV is finding out where they hid stuff. The only real way to do that is to spend a weekend or three. Tear this apart, tear that apart. Look here, look there. If you are really organized, take a lot of pictures. Eventually you will have a pretty good idea of what was hidden where on your build. You also just *might* find one or two things that could use some attention.

Why do it this way? There's a pretty good chance that something eventually will go weird at about 3AM. Doing all the looking then is not ideal .....

Best bet on the bus bar is up at the front of the trailer. The 7 pin cable and the battery cable both come in up there. All of the brakes and lights join up at that point. Is it under this or under that? Only one way to find out ....

Bob

[kmrice]

Originally Posted by uncle_bob

Hi

One of the fun parts of owning an RV is finding out where they hid stuff. The only real way to do that is to spend a weekend or three. Tear this apart, tear that apart. Look here, look there. If you are really organized, take a lot of pictures. Eventually you will have a pretty good idea of what was hidden where on your build. You also just *might* find one or two things that could use some attention.

Why do it this way? There's a pretty good chance that something eventually will go weird at about 3AM. Doing all the looking then is not ideal .....

Best bet on the bus bar is up at the front of the trailer. The 7 pin cable and the battery cable both come in up there. All of the brakes and lights join up at that point. Is it under this or under that? Only one way to find out ....

Bob

Thanks, Bob. That's good advice, as always, and I will be do some looking, as soon as it cools off a bit. One problem is that I have no idea what the DC Bus bar I am looking for looks like. Does anyone have a picture to share? I know mine might be different, but a picture of one would probably help me find mine.

Thanks,

Karl

[Troutboy]

https://www.airforums.com/forums/att...9&d=1490756159

Not sure if this will work, if you go to that link you will see a picture of all those wires Bob talked about. The bus bars are where the wires come together, it’s a :bar” that the wires terminate against. There should be a red wire one, and a white wire one

[kmrice]

Thanks, Troutboy, that's a big help. I'll see if I can find something similar on my AS. I'm trying to figure out if installing a DC/DC charger is something I could do by myself; our AS dealer is not close and is not, in my experience, very good at electrical modifications. Your help, and Uncle Bob's, is much appreciated.

Best,

Karl

[thedantons]

I am in the same boat. Now that I understand the concept of DC to DC charging, I am not 100% confident in my installation skills. I have found a company that is a Victron dealer and they instal/upgrade electrical systems in work vans and campers. I am planning on reaching out to them and see what they would charge. If the price is reasonable, I will just pay them. If it is outrageous, I will keep talking to people I know and meet and maybe I find someone that will “help” and guide me.

Everyone one here has been a wealth of information and I have learned a lot.
Thanks

Scott

[JeffKim]

Originally Posted by kmrice

Thanks, Troutboy, that's a big help. I'll see if I can find something similar on my AS. I'm trying to figure out if installing a DC/DC charger is something I could do by myself; our AS dealer is not close and is not, in my experience, very good at electrical modifications. Your help, and Uncle Bob's, is much appreciated.

Best,

Karl

I'm attaching a couple pictures of our 25' 2023 GT which I assume is similar. You're looking for the "Caution Box" usually in a rat's nest. If you take the cover off, in the second picture there is a black wire going to the positive bus bar. That is the 7-pin charging wire.

A couple of other comments (FWIW):
1. I tried adding the Victron DC/DC Orion 12|12-18. It's not too difficult but I pulled my hair out trying to get it to work. I finally figured out our Audi Q7 is fused to 15A (no idea why) and 18A draw blew this fuse, so this might be something to check out on your TV. I'd guess this isn't a problem with most vehicles.

2. I saw mention of upgrading to the WFCO AD charger. There's a long thread dealing with this and trying to get it to detect lithium batteries. It is a PIA. I'd strongly recommend swapping out the charger for either a Progressive Dynamics or if you're a Victron fanboy like me, the Victron IP43 Charger is a nice upgrade since it plays with all my other Victron VE.Net Smart equipment. Both require disconnecting the existing charger, mounting the new charger and doing some rewiring.

An aside, I started out with average household repair skills and after help from the forums and google, some mistakes, the right tools, and patience I've been able to do most any electrical upgrade myself (and Wi-Fi). I also learned a ton about how things work in the AS, solar, basic electrical. It can be frustrating but very rewarding. People on the AS forums are fabulous resource.

[kmrice]

The weather has cooled down and I found the 12 V DC Panel in the forward compartment under the right hand bunk. (I'm trying to insert a photo to this message but can't figure out how.)



Unfortunately, the Inverter is installed on top of the DC panel; you have to move it to get at the box the panel is in. Not sure if I have the confidence to unattach it from the wall of the trailer to get at the panel. There are a lot of wires I could mess up.

Need to think this over a bit. Thanks for everyone's help.

Karl

[kmrice]

Here it is:



That's the inverter above it.

Karl

[JeffKim]

Originally Posted by kmrice

The weather has cooled down and I found the 12 V DC Panel in the forward compartment under the right hand bunk. (I'm trying to insert a photo to this message but can't figure out how.)



Unfortunately, the Inverter is installed on top of the DC panel; you have to move it to get at the box the panel is in. Not sure if I have the confidence to unattach it from the wall of the trailer to get at the panel. There are a lot of wires I could mess up.

Need to think this over a bit. Thanks for everyone's help.

Karl

Ouch, yes that's not very convenient. The inverter doesn't have too many connections and they are obvious where they go if they detach. So you might be able unscrew it and move it out of the way. The screws on my 12V box were difficult, I ended up drilling some out since I couldn't get too them very easily and they are tight.