Tow vehicle not charging new lithium battery

Rubine1

Hello: 

The truck does not charge the lithium battery to the RV when traveling, but the battery charges when hooked up to shore power or the solar panels. We arrived at our camp spot with barely any power. I’m wondering what could be the problem? All the fuses and the 7-point plug on the vehicle seem to be good.  The converter was changed to a lithium compatible WFCO model.  Any thoughts?   Thanks

pthomas745

What trailer and what year?  Not all tow vehicles charge any sort of battery.

Grumpy_G

Also, is there anything turned on in the trailer, e.g. fridge ? 

Rubine1

There was nothing turned on it the trailer. Wee drove for 66  hours to arrive at a mostly dead battery.
We have a 2018 Boondock 320

Rubine1

We drove for 6 hours. 

pthomas745

What are you using to measure your battery?  What do you mean by "mostly dead"?  A multimeter? What exactly?

Sharon_is_SAM

Was the battery fully charged before travel?  

What was running in the TaB while towing?
Have you checked your 7 pin voltage on pin # 6 (the charge wire)?  

stp2136

Unfortunately most tow vehicles won't charge trailer batteries effectively because the 12V charge line wiring to the connector plug is too small, usually #16 or so.  It would need to be at least #10 to avoid too much voltage drop. If you have a 3 way fridge running on 12VDC it will draw 10 - 12 amps, most of which will come from the trailer battery because the voltage drop from the TV alternator is too great.  Therefore a six hour trip will consume ~3/4 of a 100 AH battery.

AnOldUR

Sharon_is_SAM said:

Have you checked your 7 pin voltage on pin # 6 (the charge wire)? 

Found this online, but not sure if it's generic to all tv/trailer combinations?

Since I'm not getting any significant charge advantage from my Jeep, I'm thinking about disconnecting the "Aux 12V +Charging" wire to prevent the trailers lithium from trying to balance voltage with the Wranglers non-lithium. I have 12V's at the #4 truck connection even when the vehicle is not running.

Rubine1

Thanks for all your comments and support. Nothing was running in the Tab - The battery was not fully charged when we left on the trip. I was anticipating a full battery from the TOW  vehicle.

I will check the charge wire at the 7-pin. This particular issue seems to be  specific to the new lithium battery. We did not have this issue with the lead acid.  

I also read somewhere else the following:

Modern vehicles have a “smart” alternator that only charges the car battery when the vehicle computer determines that the battery needs juice. Sometimes these smart alternators don’t play well with trailer batteries because they either don’t detect the need to charge the battery or they trailer battery isn’t low enough to need the charge.

When we ordered our camper, we upgraded the battery charger/controller specifically to avoid this problem. The battery controller is programmed to always tell the tow vehicle computer “battery needs juice” so we don’t have an intermittent charge/no charge problem.

Tabaz

I experienced the same issue with my 2010 Ford Expedition not charging the T@B batteries while in transit.  Ran a dedicated #10 gauge wire from the battery to a quick disconnect near the hitch.  Always arrive with a fully charged battery since this mod.

https://www.amazon.com/OrionMotorTech-Battery-Connect-Disconnect-Recovery/dp/B074J5DS33/ref=sr_1_5?keywords=30+amp+quick+connect+plug&qid=1692543542&sprefix=30+amp+qui,aps,161&sr=8-5&th=1

Grumpy_G

Rubine1 said:

The battery was not fully charged when we left on the trip. I was anticipating a full battery from the TOW  vehicle.

That might have been a bit optimistic. There are a number of things working against you. Typical LiFePo charging voltage is 14.2V or more and while batteries do charge at lower voltages it will result in less than 100% charge. Depending on the age of the tow vehicle it might only run 13.6V. Newer smart alternators sense the current at the tow vehicle battery and might turn down voltage as low as 12.4V. The other hurdle is the already mentioned voltage drop in the wiring to the tow vehicle connector, and also from the plug to the battery. Remember voltage drop is proportional to current, so higher current equals larger voltage drop. The battery may want to suck in 20A or more, but the effective charging voltage drops and it becomes much lower. It basically finds an equilibrium where the charge current is small enough to not drop voltage below what is needed to facilitate some charging.

Personally I always start with a fully charged battery and the tow vehicle can easily keep it topped off while driving.

Rubine1

Tabaz and Grumpy_G (and everyone) Thanks for the info. I will try the dedicated wire as well making sure battery is toped off before leaving.  I'll report back after the next trip. 

pthomas745

One more thing to add is: what are you using to monitor your battery? You may not have a Victron solar controller ( if you have installed solar) but a multimeter will give you a clearer picture of what is happening to your battery state of charge.

subfreq111

If your alternator is making 14V at the engine going down the road, it's likely 12.5V or less by the time it travels through 16awg or smaller wire 20 feet to the back of your TV, which is less than your Li battery needs to charge. If you need to depend on your TV to charge the battery, you probably need a DC-DC charger designed for Li batteries.

BrianZ

I don't know if this sheds any light on anything, but when we were leaving the campground with a 100W solar panel on our TV roof and victron solar charge controller & victron battery monitor both near the battery (150 AH lead acid), here's what the Victron monitors showed..

I concluded that both TV (~6A) & solar (~5A) were contributing a charge current.
PS: Our TV battery is connected directly to the 7-pin socket.

GregChris

2021 320s, 2019 Toy Highlander. Drove 6 hrs to Mi with the Iso therm on #2. When we got there the fridge was cold, and the battery fully charged. No Lithium.

AnOldUR

I ask this question here first since it's sort of on topic. What is the easiest way to disconnect "Aux 12v + Charging" circuit from the 7-pin wiring in a 2020 320S? If I do this, will it change anything other than charging trailer batteries from the tow vehicle and powering 12V items in my T@B from the tow vehicle? (I'm hoping it's as simple as pulling a fuse, but asking here before tracing wires to locate it.)

note that my old Wrangler does not have an isolation relay, the charging pin is always hot.

Grumpy_G

I'd think the easiest would be to disconnect the charge wire in the junction box under the front of the trailer. Having said that I advise not to do this in case you have to hook up the trailer with its battery fully discharged as the emergency braking system needs battery power. 

AnOldUR

@Grumpy_G , I hadn't thought about emergency braking and a dead trailer battery not getting a charge from the tow vehicle. It's something to consider, but I'm thinking that rooftop solar would compensate for that.

I'll take a look in the junction box, but wondering about identifying the charge wire. This chart that I posted earlier has colors on the contacts. Do they correspond with wire colors? If so, it'll be fun trying to get my wife to crawl under there to help this colorblind guy find the correct wire.

Edit to say that the picture below may be a good alternative. Anyone want to point out the charge wire?

Yoshi_TAB

Hi, I can’t , but as a suggestion, you could do a continuity check between each of those three wires and the 12v pin charge wire in the trailer harness.  Because of the distance you could use a  jumper wire  to reach (disconnect the 3 wires from the number 6 position and connect a jumper to each of the 3 wires , one at a time)

AnOldUR

I'm thinking you're right @Yoshi_TAB. I thought it would be simple, but my wife just got home and let me know that the #4 contact is red and that there are several red wires in the junction box. Have to use the multimeter to be sure.

My situation is different from @Rubine1 in that I'm not looking to get any charge from my tow vehicle. Although he did mention solar, what I may have missed is if he has rooftop solar to help charge his battery while on the road as @BrianZ illustrated above. It's probably not necessary, but I want to totally seperate my trailers lithium from the tow verticals non-lithium batteries.

elbolillo

@AnOldUR You really should just be able to disconnect the charge wire. It should be attached to the second stud from the right.

Horigan

When my brake controller was installed in my TV they included a fuse for both the 12V supply and the brake control wire under the hood.  There should be a fuse for those long 12V wire runs from the battery to the 7 pin in back of the TV.  I just pulled the 12V fuse to alleviate any concerns with draining my Tab battery into my TV battery.

Yoshi_TAB

Hi @AnOldUR,

At one point , I was looking to do the same in my Grand Cherokee after I installed lithium batteries.  I chased down the wiring diagram for my WK2 and found a dedicated line from  fuse #30 /30A to the 7 pin…maybe your model is the same??.  

AnOldUR

@Horigan. We had the Airstream dealer that we purchased our used T@B from wire our Wrangler for the 7-pin. I was just outside searching for a fuse, but couldn't locate it. Hoping there's one somewhere, but will have to look harder.

@Yoshi_TAB. We also tow with my wife's Cherokee Trailhawk. I'll bet we have the same dedicated line from the fuse box. 

@elbolillo. After Jean helped me out with the colors we were pretty sure it was the second from the right in the picture like you said. Thanks for confirming.

Question, there are three other wires at that connection, two more red and one black. My guess was one wire going directly to the battery for charging and one going to the cutoff switch to supply 12V power to the trailer. This would allow the trailer battery to charge regardless of the switch position? Even if that is correct, it leaves the question of where the forth wire goes?

What I want to know is if simply disconnecting the wire from the 7-pin harness will mess up something else?



Might have to contact nuCamp, but hoping for a quicker answer from the forum.

Yoshi_TAB

Hi,

 The four wires are for 1. From battery charger from the WFCO. 2.  On/Off battery switch 3.  Trailer Electric brake power 4.  Trailer tow harness.  

IMO disconnecting the 7 pin wire won’t harm anything.  That is often done when a DC/DC charger is installed.

SLJ

Yoshi_TAB said:

IMO disconnecting the 7 pin wire won’t harm anything.  That is often done when a DC/DC charger is installed.

My Bluetooth brake controller is powered by the 7 pin's 12 volt line from the battery.  If you have a wireless controller check.

Also, my tow vehicle has a heavy duty alternator and charges/supplies 5.5 amps (~72 watts) to my T@B with no DC-DC controller necessary. It runs my DC fridge and has enough left over to top off and keep the batteries at 100%. I have a 25 amp switch/breaker on the feed at the battery.

AnOldUR

Thank you @Yoshi_TAB. What had me messed up were the color codes on the diagram I posted earlier. I was looking for a red charge wire coming from the harness. If I'm now correct, it's the black wire on the lower left that's the charge wire.

The bottom right wire (not sure of color) traces out to the emergency brake switch. One of the two (red?) on top goes to the battery switch so that if it's on, the emergency brakes will be engaged if the pin is pulled. The other goes to the WFCO so that when on shore power it will always charge the tow vehicle battery (if plugged in), but only charge the trailer battery if the battery switch is on.

All this to say that removing the black wire will isolate the tow vehicle battery from the trailer.

Yoshi_TAB

Hi, Like many find out , the RV industry does not seem to be consistent with wire color for DC…red, black, green or some combination spliced together (found in my ‘21 TAB)..makes trouble shooting and wire chasing more challenging… which, I thought you said you were color blind so that makes you no more challenged than the rest of us 

Yoshi_TAB

Hi,

On another note, I hate that the battery switch has to be on for the Ebrake to work.  To me, that is a safety design flaw.  It should be hardwired directly from the battery independent of the switch.  If one was doing a hazard failure analysis, you would not rely on a human being to do something for a safety critical item.  When I moved my batteries inside, the wire from the battery goes directly to the  #6 post in the junction box so it’s always powered independent of the battery switch.