DC-DC charger required?

rturnerpg

Do I need a DC-DC charger to protect either the tow vehicle alternator or the lithium batteries when they are being charged while driving? 2023 T@B 400 BD with the lithium upgrade. 2020 Ford F150 w/ 3.5l ecoboost engine. TIA!

CharlieRN

Since there is some substantial disagreement about whether a DC-DC charger is truly needed to protect the alternator & charging system of the TV when using Li batteries, the answer to your question is probably "No."

That said, and regardless of which side of the argument you find more persuasive, my view is a charger provides considerable insurance against damaging your vehicle's charging at fairly modest cost. In addition, the charger will help to ensure that both your house batteries and that of the TV get fully charged.

You can buy a decent 20A charger for about $100, and the other needed components (cabling, connectors, fuse/breaker, etc) will set you back another $50 or so. A new alternator, or even a rebuild (if you can find one), will surely be more than that, not to mention the inconvenience of having your vehicle out of commission for at least a few hours.

SLJ

I've had a 100AH AGM battery charging off the tow vehicle and it's AGM battery for two years with no problem. I have a heavy duty alternator and I installed a gauge to monitor charging voltage. I will be switching to 200AH of lithium this Spring and will be adding a DC-DC charger. I expect the lithiums to draw more charging plus being a different type of battery from the TV, I don't want to mix them and risk a problem. As stated above, $100 is pretty cheap protection both for the alternator and the much more expensive lithium batteries.
I also don't really trust the WFCO controller in the long run so I won't be swapping it out and will be adding a good AC Lithium charger for keeping the Lithiums charged when plugged into shore power.

Yoshi_TAB

Hi,

Like others have said, you'll find folks on both sides of the fence.  I've done a lot of research on this and the overwelming answer is no, unless you desire to  charge your Li batteries from your tow vehicle when they are fairly discharged.  I've have not read about doing damage to the batteries, just that you can't fully charge them or this possible damage to your charging system.  I have a Jeep Cherokee and have seen the measured current on a fairly discharged Li battery and it was only around 21-23 amps.  My 7 pin positive wire has a dedicated 30 amp fuse so anything above that, the fuse will blow. The wire is rated for 30 amps.   Here a video with some real life testing and other info. I found interesting.  If it makes you feel more comfortable, you could also pull your 7 pin charge fuse.  Best wishes.

DC to DC charger NOT required for big Lithium Battery - YouTube

AndreO

For me the arguments against are irrelevant.

The cost to bennifit ratio for going without the DC-DC just isn't worth it. Not to mention any the effort, inconvenience and time without your truck to fix. You spent big bucks on your 400 and F150 so why risk it? 

AnOldUR

This is confusing. Up until now I had thought that the only disadvantage to not having a DC-DC charger was slower charging time. I hadn't read about alternator damage with lithium batteries. Researching, I'm not finding an answer specific to our setup.

Our 2013 Jeep Wrangler has a new AGM battery and we have two 100Ah LiFePO4 batteries in our 320S T@B. We may go with a DC-DC charger in the future, but don't want to harm anything before then. We have solar and a NOCO GENIUS10 to top off the lithium's.

We're heading out for an extended trip in a little over a week. Like @rturnerpg, I'd like to know if I need to be concerned?

Horigan

I suspect the long, relatively thin wire run from the alternator to the trailer battery would provide sufficient protection/resistance.  I did put a DC to DC charger in my boat after installing a lithium house battery due to the close proximity of all the components and the large wire sizes.

pthomas745

If blowing up alternators was a big issue, every lithium battery would warn against it.

Seems to me that the whole issue is owners deciding their lithium battery must be fully charged at practically all times, and that means special charging equipment, new converters, etc.

If you are using plenty of lithium battery amps overnight, and pulling out the next morning, maybe a DC-DC charger might be worth it.  I think for most owners, this might not be the case.

I can also picture many new owners looking to replace older lead acid batteries looking at all this lithium battery talk (special charging, heating pads, new converters, and on and on) and deciding, nope, I'm sticking with AGM.

CharlieRN

AnOldUR said:

This is confusing. Up until now I had thought that the only disadvantage to not having a DC-DC charger was slower charging time. I hadn't read about alternator damage with lithium batteries. Researching, I'm not finding an answer specific to our setup.

Our 2013 Jeep Wrangler has a new AGM battery and we have two 100Ah LiFePO4 batteries in our 320S T@B. We may go with a DC-DC charger in the future, but don't want to harm anything before then. We have solar and a NOCO GENIUS10 to top off the lithium's.

We're heading out for an extended trip in a little over a week. Like @rturnerpg, I'd like to know if I need to be concerned?

It is indeed confusing, but I suspect that you don't really need to be concerned.

My understanding is that lithium batteries can call for a lot of power under some conditions, such as when deeply discharged. It's possible that the demand could exceed the ability of your alternator to provide that power and should that condition occur, your alternator could be damaged. From what I've read, most alternators have a high enough output that this is unlikely to occur with a modestly-sized house battery bank, such as your dual 100Ah setup. For most, adding a battery isolation device or a DC-DC charger is roughly analogous to using a belt and suspenders.

My point in advocating using a charger is not that it's really needed under most circumstances, but that it's relatively inexpensive insurance to prevent possible damage and the cost and inconvenience of the associated repair. Many, probably even most, folks don't bother and never have a problem.

Here's a link to a BattleBorn video that you may find helpful.

RTWCTS

In the BattleBorn video link from @CharlieRN, the company states a threshold of three batteries not being an issue and anything over that they recommend system protection. How does this square with the new TAB 400 upgrade to four lithium batteries? Are these new owners being advised to upgrade their TV electrical?

Edit to add:
We are getting the 100AH version and are planning to add more batteries ourselves to increase the time we can dry camp without sun. No current plans to upgrade the inverter though.

dsfdogs

While I didn't purchase the lithium upgrade for my '23 400, I'm adding a second battery and Victron inverter/charger like yours @rturnerpg. I will also be adding a DC-DC charger, however, it will still only pull power from the 7-pin. (To save money, I won't be wiring it to the tow vehicle alternator). This will boost the output from the 7-pin, have a lithium charge profile and will ensure no power back feeds to my vehicle. If/when I add more batteries, I expect to wire it to the alternator. With only 185 watts of solar, the DC-DC seems like a good thing to help the batteries, especially as I'll have the 12v fridge running in transit.

MuttonChops

Interesting discussion, am confused by a few references of

DC-DC connected 'directly to' alternator.

My Renogy DC-DC charger installation manual clearly states:
"The Alternator will not be connected directly to the input of the DC-DC. The alternator must be integrated with the starter battery . . ."

A typical installation being:

The attached PDF file shows how a typical vehicle Alternator/Battery/7-Pin system is wired.

dsfdogs

Somehow I thought it could be hooked up to either?? I'm not an expert, that's for sure!
Here is a video from All About RV's in which he says "alternator" but then indicates the size wire attached to the battery.
Here's a real good video from Love Your RV on 7 Pin Cable Charging tests

CharlieRN

As the schematic shows, the charger is connected only indirectly to the alternator, through the TV battery. It's not shown in the Victron illustration, but would be a good idea to wire in a fuse or circuit breaker as indicated in the pdf schematic.

RTWCTS

I read the diagram posted by @MuttonChops as the DC-DC charger in parallel with the starter battery and there is a direct current path from the alternator.

MuttonChops

RTWCTS said:
I read the diagram posted by @MuttonChops as the DC-DC charger in parallel with the starter battery and there is a direct current path from the alternator.

Correct.  What is important is that the 'starter battery' is indeed there . . . . the DC-DC is not the only connection to the alternator.  The extra battery load provides some type of protection to the alternator.

So it could be said; connect to the alternator but that would not be a full and accurate statement.

Horigan

A vehicle alternator is connected directly to the vehicle battery, so you are connecting to both anyway, whether you connect near the battery or near the alternator.  Most 7-pin wiring is connected directly to the battery, with a fuse, and is in essence also connected to the alternator.  

I think overall concern is moot since there is very likely sufficient voltage drop in the wiring from the alternator, through the 7-pin wiring, to the trailer battery to preclude a high current going to the lithium battery from the alternator.

ckjs

Horigan said:

 ….  

I think overall concern is moot since there is very likely sufficient voltage drop in the wiring from the alternator, through the 7-pin wiring, to the trailer battery to preclude a high current going to the lithium battery from the alternator.

I agree. Also, the 30amp fuse on the positive wire to the 7-pin (you do have one, right?) would protect the alternator and the rest of the car wiring

RFraer

I was also concerned about the amp draw through the 7-pin. My vehicle (Ram 1500) only has 12ga wire to the connector. I spent approximately $400 for a Victron 30amp DC-DC charger and the wiring (6ga) and connectors to run from the vehicle battery to the camper batteries (600 amps/ 7200 watts). To me the benefit was not only vehicle wiring protection but mainly the 360 watts I can put into the batteries for every hour the vehicle is running. The disadvantage is I now have a second connection to make when hooking-up.

RTWCTS

@RFraer did you use an isolated or non-isolated Victron 30Amp DC-DC charger? I understand the basic grounding difference, just not sure of which is best in a towing setup. Thanks in advance...

DenisP

I opted for an isolated Victron 30 amp DC-DC charger, 6ga wire from TV battery with Anderson connectors for my 2018 400 with 200 watt rooftop solar and two 100 ah heated BB. Under the majority of situations the solar maintained the batteries charge prior to the DC-DC charger.  But in the instance of low /no solar gain, short travel or heavier battery use the DC/DC will bring the batteries back in short order. Another issue is a shady site for several days and the need to top off the batteries, I am not a fan of generators so the quiet idle of my TV will provide a boost in a pinch. 

I must confess that I am a “belt and suspenders “ trip preparer and like the peace of mind thousands of miles from home.  We all approach camping based on our needs, camping style and finances truly a YRMV situation. 

AndreO

@DenisP,
 It seems most people select a 30 amp dc-dc charger. Can I ask if it was because of a tv alternator limitation or because Victron doesn't offer greater than 30 amp or other factors?

I put in a 50 amp for my two 100 ah lithiums. It takes slightly over 2 hrs drive time to charge from a 50% DOD and will still allow for a decent charge if I add more batteries. (Even with the fridge etc running)

RTWCTS

DenisP said:

I opted for an isolated Victron 30 amp DC-DC charger, 6ga wire from TV battery with Anderson connectors for my 2018 400 with 200 watt rooftop solar and two 100 ah heated BB.

Thanks for replying to my question @DenisP .

I'm trying to wrap my head around best practices now that we're upgrading from AGM in our old TAB to Lithium in the new one (along with an intended mod of more AH capacity).

MarkAl

I added a DC-DC to improve charging rates with my Lead-Acid trailer batteries. I probably will switch to Lithium when present batteries get old. At that time, I'll continue to get better charging while going between sites (the Lithium's can charge faster) and protect my car from the rare occurrence of a fully charged Lithium back driving into the car's system. This as described above is unlikely to be a problem. I like playing with electronics, so I had no trouble doing it.

Mouseketab

OK, similar, but different topic. I have a DC-DC charger installed on my truck. I have a set of wires into my junction box on the bottom of the T@B, then zip-tied along the 7-pin, then it hooks into an Anderson connector on my bumper (into the DC-DC charger). AGM Battery. I disconnected the charge line in the junction box from the 7-pin (capped off), and replaced it with the "hot" on the DC-DC wire set. I tied in the neutral with the rest of the neutral wires.

I bought a new T@B with factory solar (and it's own controller). If I move this wire from the old T@B to the new T@B, wiring the same way, will running the DC-DC charger this way interfere with how the solar operates?

rcarlson1957

Can only talk from a frame of reference pulling a '18 320 with 100ah lithium with a '20 Honda Ridgeline. 37 trips over 45,000 miles and no DC-DC controller. No problems whatsoever.  We're usually camping with shore power and when not use 2 portable 120w solar panels connector to solar controller in tub to handle things. Would tend to think if it was a problem then the battery manufacturers, auto manufacturers and NuCamp would mention it to prevent lawsuits. Haven't run across any mention of it from any of them. 

MarkAl

@Mouseketab I have a Victron BT networked DC-DC charger and two Victron BT solar chargers. They are networked so they distribute charging well.  However if you have non-networked chargers, they generally work fine together. Each will try to control based on the system voltage and history especially if they are MPPT. I wouldn't worry, the benefits will be there of significantly more and intelligent charging if needed.

Tabmanic

I just removed the TV cable from the junction box on TAB all together, that way there is no need to worry about the lead acid and lithium combo (13.4-14.6 not sure which way the current would flow?). I will just add a DC to DC later with it's own large cables from TV battery to Tab, the solar will keep them topped off for now.