Is a DC-DC charger needed with a lithium battery upgrade

DanSees

Is a DC-DC charger needed with a lithium battery upgrade in my 2021 Tab 320S BD? If so do I need a isolated or non isolated? Does this get installed in the tow vehicle or the Tab? Also I do not know which model is needed. I am installing 2 100 amp batteries. I have the 105watt factory solar panel with the MPPT 75-15 solar charger. I am going to upgrade my converter charger to the WF 8735AD. 
If I do not need the DC-DC charger, do I only get partial charge 80-85% when towing or will my solar help bring my batteries to 100% while towing? 
I'm sorry for all the questions, but I want to do this right & get it all done at once. I don't want to spend money unnecessarily.  I am doing this DIY. I'm quite capable of the work just need some guidance with the correct direction to go. 
Thanks

mgreen2

You probably already have a lithium compatible charge converter in the 2021 T@B. What is the model number in the camper? Charging capacity from the tow vehicle is based on what tow vehicle you have and the factory wiring. I can fully charge a lithium with my 2020 Honda Pilot.  The solar setup will fully charge the lithium with or without the tow vehicle or shore power. You would need to change the settings on the Victron 75-15 using the Victron App. I would install the batteries and see if everything works before buying or doing anything else

techietab

A DC to DC charger with isolation is ideal, but not strictly speaking necessary. I haven't gotten around to installing mine after upgrading to 2x LiFePO4 batteries. I just make sure my batteries are fully charged before leaving home, and with 10 gauge wire tapped from my vehicle battery into the 7-pin harness, I don't really seem to lose any charge while on the road. Per the Victron Smart Shunt I installed, the trailer's DC system is always running at anything from a slight to a drastic surplus in amperage depending on what my tow vehicle is doing.

I wouldn't count on the stock roof-mounted panel to bring you to 100% when driving. I've found the performance on mine to be quite lackluster and will probably be bypassing it entirely in favor of repurposing the Victron MPPT controller for external panels.

DanSees

mgreen2, I have the non-lithium converter charger WF 8735P I have already confirmed this will not fully charge the lithium batteries. My Tab was built in June of 2020 went into service 8-8-2020. My tow vehicle is a 2008 Toyota FJ Cruiser. I upgraded the alternator this past spring when my oem alternator went bad. I did not change any wiring on the TV.  I went from 100 amp to 130 amp. I noticed a quicker charging time on my AGM battery when towing.  
I began thinking that the solar would assist with charging during towing as long as the conditions are right, but I wasn't sure.

DanSees

techietab. Thank you for the reply. I think I will probably wait on the dc-dc charger. I also want to see what the stock panel will do for us. Hoping but I don't have much faith in it. I know this would be an easy addition in the future. I just feel that a suitcase solar panel & cable would be one more thin I need to find space for while traveling. I would prefer to eliminate stuff than add. 

pthomas745

The Victron controller with the panels, and any "smart" charger,  will fully charge the lithium batteries.  I can think of a few owners here with large battery banks and a lot of usage  that would benefit from a DC-DC charger that would help them when on the road in between campsites.  So, put "what and how do I intend to use in my camper and how much power will I need to replace" into your equation.

Dutch061

In my experience you will need to add a DC-to-DC Charge Controller. The main reason being that you will not experience high enough charging system voltages to do anything in charging the Lithium Batteries. I had 2 different tow vehicles on my 2020 400 BDL and neither would do anything as far as charging. 

The Charge Controller will allow you to not only boost the voltage but also will limit the amperage to prevent any damage to wiring, alternator, or otherwise. 

I used the Victron Smart Bluetooth 18 Amp, set up was simple using the Victron app and it works great! There are others, but since I had Victron for a BMV-712 and the 75/15 Solar Charge Controller, I decided to keep it simple. 

Brad

CharlieRN

We have two 100 Ah Li batteries in our 320. My understanding is that you do not need the protection of a charger if you are just using the 7-pole connector and stock harness. The wiring in that system is relatively small gauge, so cannot carry enough current to damage things. Of course, that may also mean you won't get the battery bank fully charged. We added a DC-DC charger as protection for the alternator when we added heavy guage wiring from the TV. There is some debate about the need to protect the alternator with a charger, but the charger is relatively inexpensive while replacing the alternator is pretty costly.

As to the solar capacity, the standard ~100w panel can be sufficient under ideal conditions, or if your stay is limited to a few days. You nearly always get some charging, and 200 aHrs goes a long way.  That said, we have a 200w suitcase charger and 30' of cabling that we take on longer trips so that we are sure we can charge when the T@B is in the shade, or parked facing away from the sun.

Our T@B is a 2021, so the stock WFCO will not charge the batteries to 100%. That's not really too much of a problem as lithium batteries only need to be topped off occasionally so that the BMS can properly regulate things among the cells. If we did not get to 100% with the solar, we'll use our AC charger to get things to 100% as needed.

Dutch061

Again, for me it is not the fear of passing too much amperage, my TV has 10-gauge wire for the power and ground to the connector in the back that is fused at 30 amps. It is based on the simple fact that I wasn't able to provide ANY amperage to the batteries previous to the Charge Controller due to insufficient voltage (aka pressure). Now, it does exactly what is required for voltage (14.6) at 18 Amps (aka volume).

This means that I can spend weeks at a time without shore power if I am moving around, regardless of solar output which of course is why I spent the money on 400 Ah of lithium batteries. We typically try to camp under the canopy of the trees, so it is imperative to be able to charge while traveling. 

We spent the entire month of July with the exception of 1 night without shore power. The only reason we had it that night was due to the heat and the desire for A/C. We never had any issues with not having sufficient power available, after all what fun is it when you have to spend your time fiddling around rather than enjoying yourself?

As far as Solar Panel Watts to Lithium Batteries, Battleborn recommends 200 to 250 Watts for each 100 Ah of battery bank capacity. I'm not sure what other battery manufacturers specify, but I suspect they are similar. 

Everyone has their own thoughts and opinions on this, I am not saying that I am right and anyone else is wrong. So do what you need to do in order to get the results that you are trying to obtain. I'm just sharing my personal experience with and without a DC-to-DC Charge Controller and extended usage of our 2020 400 BDL. 

Brad

dragonsdofly

@DanSees I agree with @mgreen2 about getting your LiFePO batteries in and see how they function with your type/style of camping and make any changes or upgrades later and only if necessary. With the standard OEM converter in the t@b already capable of charging the LiFePO batteries to approx 80% all you will need to do is top off the batteries. Solar can do that. It may not be in a few hrs in the winter in northern climates, but it will charge them fully. There are many variables here. Become familiar with your needs before spending a lot of cash and even more time on problems that may never be. 

I brought our now full time (30' Keystone Laredo travel trailer) home in Sept 2019 and spent nearly every available moment in it until Jan 2021 when we had a complete solar power system installed. In the interim, I studied our electrical needs, lifestyle, etc. Since this system was installed, (it is my design) we have never been connected to shore power. 600 ah of Battleborns, 1.4 k of panels on the roof, 2 50 amp charge controllers, 3,000+ watt inverter are more than adequate. We have been in Michigan since May 1st. We are not plugged in. In the past week we have been charged to 100%, depleted to 32% after 5 days of intense cloud cover and rain and now after 2 days of light overcast have recovered the batteries to 88% of charge. LiFePO batteries are supposed to do better if not always at 100% SOC. 

Define your requirements first, then move to meet them. It is the most efficient process.

Good luck with everything. 

WayneW

@DanSees  All very good questions. We also have a 2021 320S BD. We have 1 100ah lithium battery, 105w rooftop solar and a 100w Renogy solar suitcase. Our converter will get the battery to ~85% and the rooftop solar will top it off but that’s not always reliable and depends on clouds, direction of travel, time of day, season, etc. I pulled the fuse on the 7-pin charger wire because it was contributing very little w the small gauge wire and I didn’t want to worry about different lithium/lead acid charging profiles and such. The solar suitcase is always in play when we have camp set up. 

We’ve been doing fine w our system. We do almost exclusively boondocking, from 3-15 days or so. I am pondering a dc-dc charger but I think we’ll go another year and see what we think then. I would probably mount it in the trailer.  

We don’t have as much cushion as you do w your 200ah setup. You have more capacity to go w/o solar for more days and I like the idea of living w a system before adding things on. 

DanSees

CharlieRN, Do you know what brand & model of DC-DC charger you installed? Did you install it in the tow vehicle or the T@b?

DenisP

I upgraded our 2018 400 with 2 100 ah BattleBorn lithiums this spring. I already have a Victron 30a DC/DC and 200 watts of rooftop solar. The setup works well for our style of travel/camping. I also upgraded my converter to an auto detect model used in the current campers. The converter hasn’t detected the lithium batteries yet as I need to fully discharge them for the converter to auto detect. 

When I installed the isolated DC/DC charger in the tab, I ran 6 Ga wire from the TV battery to the charger with “Anderson connectors” between the TV and Tab. The solar and DC/DC charger often fully charge the batteries  during travel between campgrounds. The DC/DC charger has also been used during overcast days as we do not have a generator. 

DanSees

DenisP, this is from WFCO technical support. You may already know this but I am going to post it for you or anyone else who may read this post. I am replacing my WF 8735P converter /charger with WF 8735AD. 

 Note: if you purchase a WFCO auto-detect (AD) model, it will need to be put in lithium mode when used with lithium batteries. This requires you to temporarily disconnect your solar (if so equipped) from the RV battery, discharge your lithium battery to as low as the battery’s BMS will allow (you may want to temporarily disconnect your second lithium battery – if so equipped - first to shorten your battery discharge time), then plug in your RV and allow the converter to run through an entire charge cycle. Once finished you can confirm the switch by the color of the LED inside the WF-9855-AD, as it will have switched from green to blue. Then, after you see the blue LED and if so equipped, reconnect your second lithium battery and your solar. 

Feel free to call us for further troubleshooting assistance.

Best regards, 

Janice 

Arterra Distribution

Attn: Technical Support

2021 Aeroplex Drive North

Elkhart IN  46514 

Phone (574) 294-8997 or toll-free (877) 294-8997, option 1

Fax (574) 294-8698

www.wfcoelectronics.com

CharlieRN

DanSees said:

CharlieRN, Do you know what brand & model of DC-DC charger you installed? Did you install it in the tow vehicle or the T@b?

It is a Renogy 20 amp. Though not ideal, it was easier to install it in the T@B so I put in the right front compartment, next to the batteries (see below). The Smart Shunt is next to it. I also installed a 12v fan to help with cooling, but as far as I can tell, it's not really necessary,

DanSees

If not ideal , what do think would be a better setup? Some of what I have read is it should be close to the battery. Which is where you installed it. I also think that with it in the T@b you can tow with confidence with any tow vehicle. I could be wrong, I am just learning about the use of the DC-DC charger.

DenisP

@DanSees Thank you.  I have winterized my Tab and removed the fully charged batteries.  I plan on attending to the setting up the converter when I dewinterize next spring.

MarkAl

I recently put a Victron DC-DC non-isolated smart charger in the trailer mainly as I was not getting the charging I wanted between sites from our TV. We rarely camp where we can get enough sun to keep the charge up on the batteries, this plus the roof helps between sites. This setup allows the TV to charge with large currents without regard to the TV and trailer's battery combined voltage.  It also reduces the need to keep the wire voltage drops to an absolute minimum as the DC-DC adapts the output as needed for the trailer system - at the trailer.

We are planning in another year upgrading to lithium where I believe the different battery chemistry is better served in both TV and trailer with the isolation of a DC-DC voltages. If this is not done the two chemistries though close, will not be ideal for the TV battery system. The alternator is not designed for the Lithium charge profile and so will not efficiently charge the battery (it never was designed to charge the battery as efficiently as a charger will). I'm guessing that a fully charged Lithium can back charge the TV battery at potentially high currents due to its more stable voltage output and high output current. Though I haven't heard of a problem with this so I may be wrong.

Our camping style is to rarely plug in and the trailer rarely sits in full sun so we try to optimize where we can. This is good for us and I get a kick out of doing this stuff. This is very low on the list for lead acid trailer systems and more useful for the Lithium crowd but usually not needed.

Dutch061

@CharlieRN install, this is exactly what is recommended to have the Charge Controller as close to the battery bank as possible. Mine is adjacent to the Power Distribution Center because I didn't want to run an additional wire from the PDC to the battery bank under the bed. 

I used Victron as mentioned for ease of configuration via the Victron App and Bluetooth.

Again, it depends on several variables with the biggest one being how you use your camper. Lithium and the associated changes only benefit those who boondock regularly, otherwise it is spending money that could be used for other things. 

Brad

WayneW

@CharlieRN  As I stated above, I haven’t installed a dc-dc charger but am thinking about it. I looked at the same one you have, the Renogy 20 amp unit. 

I thought you had to have a wire running from the small green junction box to a switched 12v source so the charger could tell when the vehicle was running. Renogy calls this the “D+” terminal. In the manual, Renogy states “ The DC-DC will not power on or operate until the D+ ignition cable is connected to the ignition circuit where it will detect a 12V source to operate ON.“. But I see you have no wire coming from this. 

I’m only partially literate when it comes to electricity. What am I missing?  Thanks. 

MarkAl

The Victron that I have has an external wire option to sense the "ON" condition but also can be configured to use the input voltage level and (I believe) the change to trigger the DC-DC charger ON. I use the wireless option. It seems to work fine in my few tests.

As a side note, it's interesting to see the tradeoffs in battery input power as the DC/DC, and the two MPPT chargers change power levels as I shade one or two of the inputs. To see this the Battery needs to be pretty low and some heavy current systems running. Otherwise as been stated elsewhere the VE system works the most powerful input first before sucking from the others to meet the battery/system needs. It balances successfully. The issue I find is the charger slows down the power quite a bit before 100% so the battery needs to be fairly low. This will change when I move to Lithium.

If any battery / settings expert is out there, I could use help in changing my "Standard" Victron Lead Acid settings to something possibly more correct (DM would be good).

CharlieRN

WayneW said:

@CharlieRN ..

I thought you had to have a wire running from the small green junction box to a switched 12v source so the charger could tell when the vehicle was running. Renogy calls this the “D+” terminal. In the manual, Renogy states “ The DC-DC will not power on or operate until the D+ ignition cable is connected to the ignition circuit where it will detect a 12V source to operate ON.“. But I see you have no wire coming from this.

Edit: Added link to earlier thread posting about my battery project. The photo I used above was from that thread, and the text in it indicates that the shot was indeed prior to adding the energizing circuit.

https://tab-rv.vanillacommunity.com/discussion/15437/yet-another-lithium-battery-installation#latest

Yes, you do need that extra switched circuit wire. I think I took this photo before I ran it to the charger.

DenisP

My Victron DC/DC charger is configured to read the battery voltage and when it exceeds 13.2v the charger begins to charge. It is not connected to the ignition. The combination of Victron solar controller, BMV172, and DC/DC charger work well together and using Victron app allows easy monitoring and configuring the system. The BattleBorn batteries charge well when traveling between campsites. 

CharlieRN

DenisP said:

My Victron DC/DC charger is configured to read the battery voltage and when it exceeds 13.2v the charger begins to charge. It is not connected to the ignition. The combination of Victron solar controller, BMV172, and DC/DC charger work well together and using Victron app allows easy monitoring and configuring the system. The BattleBorn batteries charge well when traveling between campsites. 

That's a big benefit of the Victron DC-DC charger and a good argument for the unit, along with BT and the better Victron warranty. The only real drawback is cost; it is more than double the Renogy.

DanSees

After a lot of research & everyones info here, I decided to get the DC-DC charger. Mostly for saftey reasons of taxing the tv wiring/alt/& battery.  I ordered the Victron Orion 12/12/30 amp along with 2 Lion Energy 1300 lithium batteries @ 100ah each & a WFCO controller/charger with auto detect for the LI batteries. We do about 50/50 boondock, however when in campgrounds we tend to seek out the ones that have no hookups. We do a few trips a years of about 2 months at a time sometimes moving every other day & sometimes staying for 5-7 days at a time. I think this setup will work much better for us than the current AGM 125amp battery that barely makes it through the night with only our frig on low 1 or 2. Some parasetic drains & maybe a cell phone charging.  

Next comes the design of where to actually install the batteries & the DC-DC charger, running the wiring & making it a clean, safe setup. I'm using the wiring diagrms found on this post along with my own knowledge to confirm that I am setup correctly. https://tab-rv.vanillacommunity.com/discussion/10532/lithium-or-agm-battery-mounted-inside-a-320-cabin/p1  Any additional advise would be greatly appeciated.

DenisP

Sounds like a nice plan. Once completed the battery anxiety should be a thing of the past. 

klenger

I believe that it is always best to install any battery charger (solar, DC-DC, or AC to DC) as close to the batteries as practical so that the charger(s) "see" the battery voltage as close as possible.

Regarding the need for an isolated DC-DC charger, (FYI I have never actually used one but am rather proficient with electronics) an isolated DC-DC converter adds isolation to the ground points of the two systems.  The (+) sides of the DC-DC converter are inherently isolated as that is the purpose of the device. An isolated DC-DC converter would be required if the ground potential of the two DC systems was not the same. This is not the case of a trailer and a tow vehicle as the grounds for the trailer and tow vehicle are both tied to chassis for each and tied together with the 7-way cable. Furthermore, the hitch itself adds another (but not necessarily dependable) ground connection between the trailer and tow vehicle. 

DanSees

Klenger I do believe I could have saved a little bit of money by purchasing the non-isolated & after I bought it I started questioning my purchase. But either way isolated or non-isolated I will be covered if I were to lose the ground connection between the two & I never trust the ground at the hitch. 

Horigan

The primary ground is through the 7-pin connector, which is as robust as the 12V power coming through the connector.

DenisP

I wired my Isolated Victron  DC/DC charger with 6 g wires directly with my TV battery and the charger bypassing the 7 pin connector. I wanted to minimize voltage drop with the lesser gauge wired 7 pin connector.