Forum Discussion

orourkmw's avatar
orourkmw
Explorer
May 13, 2022

Lance TC - lithium - DC-DC charger question

I’ve just purchased a 2020 Lance 975 that will sit in my 2022 F350. I have to install the Lance 6-pin at the front of my bed. I will also replace the two 12V lead acid house batteries with one 200 ah LiFePO4. The Lance has a battery separator, which appears to be installed just upstream of the house batteries. I think I need a DC-DC charger to protect the 270A alternator (as well as to get charging benefits), and am considering 30A-40A. Lance specifies at least 8 gauge hot and ground wires from the truck to the 6-pin. I am thinking that to protect the alternator from a large current draw, ideally I should run 2 or 4 AWG wire from the truck battery all the way to the DC-DC, and back, and not connect to the 6-pin plug (so skip the 8 ga). I think CamperJeff explained the potential complications of feeding the 6-pin. I would mount the DC-DC at the battery box, which is ~4 foot from the pin connector, so I’ll have to see how to feed the wire through. My questions are these: First, am I understanding this properly? If I can keep the battery separator in-line and ahead of the DC-DC, can I avoid the D+ signal wire that the DC-DC uses to isolate truck from house? I think the DC-DC only takes as large as 6 ga, so I’ll need to narrow down as close to the end as I can manage. Is there still a risk of overheating when running lighter gauge wire between the relatively short run from the battery isolator through the DC-DC to the LiFePO4? Any guidance would be appreciated.
Truck Campers
  • Lwiddis's avatar
    Lwiddis
    Explorer II
    May 13, 2022
    If your roof has sufficient space, solar would be easier. Another option is a AC to DC Lithium charger if your truck has a 120 volt plug that is hot when driving. Mine is a 10 amp charger.
  • theoldwizard1's avatar
    theoldwizard1
    Explorer II
    May 14, 2022
    You are overthinking this !!

    If you install a DC-DC charger (highly recommended) immediately upstream for the batteries you will no longer need a battery separator. You should not need larger wire either. Your DC-DC charger will act as both a separator and limit the amount of power that can be drawn from the truck.

    Add a gauge and shunt on the output side of the battery so you know how much charge it has.
  • orourkmw's avatar
    orourkmw
    Explorer
    May 14, 2022
    Yeah, my wife accuses me of over thinking it often! So I could just use the 8 gauge wire and go into the 6-pin plug? That would sure be simplest.
  • time2roll's avatar
    time2roll
    Nomad
    May 14, 2022
    Protect the 270 amp alternator from what? I bet the charge line fuse is 40 amps and it will not have any trouble.
    I can't tell if the plan is to push more amps or to limit-reduce amps.

    I recommend to connect as designed and see what goes. I think the OEM system will be fine.
  • orourkmw's avatar
    orourkmw
    Explorer
    May 14, 2022
    My main goal is to make sure I don’t burn up the alternator and get stranded. But also, on my last two campers the charge I got from my alternator was minimal. With a compressor fridge (NovaKool) on my last camper I would end a day driving 10% under the SOC where I started, even with 200 W solar. I would like to have a 30A charge or so go into the batteries while we’re rolling (even though I’m back to a 3-way fridge). It sounds like the system as described will be ok on both counts. I’m ordering the Victron 12-12/30 amp Smart DC-DC, and will hook up 8 ga 6-pin. Thanks for the clarity.
  • theoldwizard1's avatar
    theoldwizard1
    Explorer II
    May 14, 2022
    orourkmw wrote:
    Yeah, my wife accuses me of over thinking it often! So I could just use the 8 gauge wire and go into the 6-pin plug? That would sure be simplest.


    time2roll wrote:
    Protect the 270 amp alternator from what? I bet the charge line fuse is 40 amps and it will not have any trouble.


    What he said ! The DC-DC charger also limits the power draw.

    Next truck, don't waste your money on the oversized alternator.
  • mbloof's avatar
    mbloof
    Explorer
    May 14, 2022
    +1 over thinking it.

    Back in the day, my buddy bought a Lance. Included in the installation was a 8AWG wire ran from the battery to a 50-100A solenoid (switched on/off with the ignition/engine running) a 40-50A fuse and 8AWG wire from the fuse to the Lance connector. He could easily run his fridge on DC and/or charge his house battery(s) with the truck running. Granted this setup won't charge the camper battery(s) all the way because of voltage drops/loss of the wiring+connectors.

    Keep in mind that for current to flow there needs to be a voltage difference.

    Fast forward to 2021 and LiFePo4 batteries are all the rage. While IMHO they are a better option then FLA batteries by all accounts, they do need/require a higher charge voltage then FLA batteries.

    While there are a number of options available to accomplish this a popular one is to employ a DC-DC charger. (there are a number of different OEM's that make them and each have a number of different models to choose from)



    - Mark0.
  • 3_tons's avatar
    3_tons
    Explorer III
    May 15, 2022
    You need only be concerned what the alternator is capable of on a continuous basis, and the accepted norm for this is 25-30% of it’s nominal rating. So for a 270a alternator, the acceptable range would be somewhere between 67 and 81 continuous amps, so having two 200a/r Lithium’s myself (based on charge monitoring…) I in this regard, I don’t see how you’ll have any kind of problem - JMHO

    3 tons
  • Grit_dog's avatar
    Grit_dog
    Navigator
    May 15, 2022
    I sometimes have to just giggle at responses like "next time don't waste your money on the HD alternator...."
  • Grit_dog's avatar
    Grit_dog
    Navigator
    May 15, 2022
    Grit dog wrote:
    I sometimes have to just giggle at responses like "next time don't waste your money on the HD alternator...."


    The only real question is what charge voltage and how many amps you'll get out of the truck's charging system, depending where you wire the custom plug to, for the 12V hot lead.
    Not whether you'll overload the truck's alternator.

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