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  1. #1
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    Charging Lithium Batteries From Your Tow Vehicle

    In another thread, the following question was raised by @Butcher :

    I have not done, but I plan on doing some type of vehicle charging system on my Ford. Dual alternators is the goal. I do not know, but with location of the alternator and the LifePo4 batteries, I will be needing much more than a 6ga wire. I suspect a separate Anderson connector is what I will be using. Again, I do not know the size wire, but I can't see myself using anything less than a 2ga and will probably go 1/0. Yeah, a huge cost but I suspect with a good connection to the steel frame of my truck, will keep the ground side a bit cheaper than the power side.

    One thing to thing about is to see if an old school Ford fender mount solenoid is a good thing to put in line. That way, the truck would be disconnected when the vehicle is turned off.
    Since charging Lithium batteries from your Tow Vehicle is not as straight forward as it seems it should be, I thought I would start a new thread to address the topic directly.

    Because Lithium batteries can accept a charge much faster than Lead Acid batteries, and many people are installing larger battery banks, charging them through the 7 pin connector is not possible, or practical.

    The best way to address the issue is to install a DC-DC Converter in the Tow Vehicle with the appropriate sized cables leading from the TV to the camper.

    The DC-DC Converter will act as a charge limiter so you don't burn out your alternator by running a charge cable direct to the camper. Because, Lithium batteries can accept charging at such a high rate, especially in larger battery banks, there is a risk of burning out your alternator because of the high current and long duration needed to charge up the battery bank.

    One of the first things to consider is where to install the DC-DC Converter, in the truck, or the camper. I chose to install mine in the truck, behind the back seat ( I installed mine on the passenger side because Ford installed part of the sound system on the driver's side). This location also allowed me to use one of the upfitter switches to control whether the Converter was on or off. I found that being able to control the Converter from inside the truck is very useful because I don't always want, or need, to charge the batteries, for example: if I have a long drive and it is a Sunny day, my Solar system is plenty capable of charging the batteries without any assistance from the truck. If you install your Converter in the camper, then the only control you have is whether you connect the camper to the Tow Vehicle or not.

    Next thing to consider is the size/charging amps of the Converter. This will dictate the size of the cables you will need. Note: because of routing inside the truck and camper, it can be a very long distance from the front of the truck where you connect to the battery to the campers battery connection. Consequently, you will probably need to increase the size of the cables you use. Note: an excellent source to determine your cable size is the "Blue Sea wire size chart" (Google that term).

    I would like to mention here, that it is possible to charge a 24 volt battery bank with your 12v Tow Vehicle by using an up-voltage DC-DC Converter, this is what I have in my truck.

    It is important that you install a fuse as close to the battery as possible to protect the new cables, be certain to consider the "surge" capacity of your Converter when selecting your fuse size. I decided to use a manually resettable (Bussman brand) fuse that met the requirements of my Converter, however, the "surge" capability of the Converter lasted longer than I expected and I kept popping the fuse, so, I needed to install a slightly larger (10 amps more) fuse (note: my cables were rated for the larger fuse).

    Another consideration is how are you going to transfer all this power to the camper. Many people choose an Anderson type connector, that was my first thought, but I couldn't figure out an acceptable way to protect the connector when not in use. What I decided to use was a two pin, "lift gate" connector that is used on commercial trucks, it is heavy duty, rugged, and I could mount it in the truck bed right next to my 7 pin connector (it looks just like the 7 pin connector). To mount this connector, I took a piece of wood (about 6" x 10") and drilled a large hole in it to accommodate the 2 pin connector, I then added a couple of 3/4 inch strips on the back side edges to accommodate the ribs inside the truck bed. I spray painted the wood with Rustoleum's Truckbed Liner to waterproof the wood. To mount this to the truckbed, I temporarily mounted the wood to the truck using self tapping screws on each corner, I then drilled a large hole in the side of the truck, using the wood as a guide for my hole saw. I then installed "riv nuts" where the self tapping screws had been to hold every thing in place.

    The final thing to consider is how you are going to control your DC-DC Converter, for me, using the Victron Converter, I was able to simply choose one of my upfitter switches that was only powered when the truck was running and ran a single wire to the Converter, when that line is energized the Converter converts, and when there is no power, the Converter sits idle. I am sure other brands of Converters have a similar method of controlling them.

    Once you make all your decisions, it is simply a matter of installing the cables and components.

    A few of the installation issues I faced, and how I solved them:

    Because I have a Diesel engine, Ford decided to fill up every square inch of the engine compartment with engine stuff, making it a challenge to find a location to install the fuse. I decided to run the cable connected to the battery, forward to the front of the truck, and mount the fuse above the headlight. This caused me to double back to route the cable to the firewall.

    I routed only the positive cable from the battery, to the base of the firewall and up through the floorboard on the driver's side and then along the rocker panel to the rear seat. Fortunately, Ford was already routing wires through the rocker panel and a channel already existed.

    I used the Chassis for the negative connection. Ford had installed a Chassis ground cable near where I installed the Converter so I ran a cable up to that point and mounted my negative cable right on top of Ford's cable using the OEM bolt.

    I ran both positive and negative cables from the output side of the Converter all the way to the battery bank of the camper. I was able to route the output cables through the back of the cab and under the truck. To cross back to the driver's side I was able to use a frame cross member. I also used plastic wire loom to protect the cables underneath the truck.

    Note: the cable run from the front of the truck to my battery bank was over 60 feet, consequently, I needed to purchase more cable in the middle of my project to reach the battery bank. This length will also factor into the wire size you select.

    As mentioned above, I chose to use a 2 pin connector similar to the standard 7 pin connector. To run this into the camper, I used 1 inch, closed, wire loom. I pushed the two cables into the wire loom and used 1.5 inch shrink tubing to connect the wire loom to the strain relief spring on the connector. This made a very nice "2nd pigtail" for the camper. I had to route this new pigtail slightly different (at the pinbox) than the 7 pin pigtail, because of the size of the cables inside the wire loom and the bend radius of the two cables. Otherwise, the new pigtail is just like the OEM 7 pin pigtail and has similar flexibility, I did make it several inches longer because of where the second connector is mounted inside the truckbed.

    Because the cables came in at the ceiling of the front hold, I routed the cables along the ceiling until I reached my electronics distribution board mounted to the backside of the stairs. This is where I made the connections to my battery bank.

    Note: because of my distance and amperage requirements, I was able to use 6 gauge cable for the entire 60 foot (plus) run. If I was charging a 12 volt battery bank, my cables would have needed to be much larger. FYI, I ran 12 volts, at 70 amps, for approximately 30 feet to reach my DC-DC Converter, I then ran 24 volts, at 20 amps (30 surge) back to the camper. I could have reduced the cable size for the 24 volt run, but with the long distance, I decided to just stay with the 6 gauge cables.

    One additional note: I don't like the fact that the connector on the camper is "hot" all the time. I tried using a Victron battery isolator as a diode to eliminate voltage at the connector, but it didn't work. I just purchased a different style diode and I am hopeful this will work.
    David and Peggy
    2019 Ford F350 Lariat, 6.7L Diesel, Dually, Long Bed
    Running with 20k Reese Goosebox (Love It) and Ford Factory "Puck" system.
    Stopping with 8,000 lb Disc Brakes and Titan Hydraulic over Electric Brakes system.
    Powering all this fun with 1200 Watts of Solar, two Tesla, Model S, battery modules, 24 volt Victron Inverter.
    2018 Solitude 310 GK

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    good write up - I have a very basic setup - just swapped the factory LA battery with a 100 Ah Li battery (left the camper converter alone as my solar charger can get the Li batter to 100 SOC). The only charging that I have from the truck is through the standard 7 pin cable. I assume I am ok as there is some current limiting device in the truck that would ensure I don't push too much current to the camper from the truck if I connect up and the Li camper battery is in a low state of charge - is my assumption good?
    2023 Reflection 324 MBS
    2022 RAM 3500 | Laramie | 6.7L HO | SRW | 4x4 |

  3. #3
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    Great summary! One question...Could you not put a switchable circuit breaker in-line on the camper side to avoid always having a hot connection?
    Chad
    2023 23LDE 965W Solar, Victron Multiplus, Solar Controllers, Cerbo GX, 4x280AH DIY Lithium Batteries, SeeLevel Tank Monitoring, Shock Absorbers (Replaced 2022 22MLE)
    2022 F350 6.7L Superduty, Carbonized Gray, Ultimate Lariat Pkg, 4WD, Crew Cab, 160" Wheelbase, 3.55EL Rear End, 3566# Payload
    Adaptive Steering, Ultimate Camera Pkg, 20" Wheels, 397 Amp Dual Alternator, ARE Topper (Replaced 2004 F150)

  4. #4
    Site Sponsor SolarPoweredRV's Avatar
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    Quote Originally Posted by Riverbug View Post
    Great summary! One question...Could you not put a switchable circuit breaker in-line on the camper side to avoid always having a hot connection?
    Yes, you could also simply add an in-line switch. However, I prefer an automated solution. It is hard enough for me to remember to turn on the DC-DC Converter in the truck, I could easily forsee a time when I remember to turn on the Converter in the truck, but not remember to turn on the breaker in the camper.

    Last Fall was the first trip we took where we had the DC-DC Converter installed. Whenever we hitched up, I would evaluate whether or not to plug in the camper to the Converter, then, I would need to remember to turn on the Converter, and, turn it off before I shut off the engine (the Converter will automatically shut itself off when I turn the truck off, I just prefer to shut it off before I shut the truck off). Honestly, I was on it about 80% of the time.
    David and Peggy
    2019 Ford F350 Lariat, 6.7L Diesel, Dually, Long Bed
    Running with 20k Reese Goosebox (Love It) and Ford Factory "Puck" system.
    Stopping with 8,000 lb Disc Brakes and Titan Hydraulic over Electric Brakes system.
    Powering all this fun with 1200 Watts of Solar, two Tesla, Model S, battery modules, 24 volt Victron Inverter.
    2018 Solitude 310 GK

  5. #5
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    Quote Originally Posted by SolarPoweredRV View Post
    Yes, you could also simply add an in-line switch. However, I prefer an automated solution. It is hard enough for me to remember to turn on the DC-DC Converter in the truck, I could easily forsee a time when I remember to turn on the Converter in the truck, but not remember to turn on the breaker in the camper.

    Last Fall was the first trip we took where we had the DC-DC Converter installed. Whenever we hitched up, I would evaluate whether or not to plug in the camper to the Converter, then, I would need to remember to turn on the Converter, and, turn it off before I shut off the engine (the Converter will automatically shut itself off when I turn the truck off, I just prefer to shut it off before I shut the truck off). Honestly, I was on it about 80% of the time.
    Yes, good points. It would definitely have to be on my camping "break down" and "set up" checklists, otherwise, I would forget it every time too.
    Chad
    2023 23LDE 965W Solar, Victron Multiplus, Solar Controllers, Cerbo GX, 4x280AH DIY Lithium Batteries, SeeLevel Tank Monitoring, Shock Absorbers (Replaced 2022 22MLE)
    2022 F350 6.7L Superduty, Carbonized Gray, Ultimate Lariat Pkg, 4WD, Crew Cab, 160" Wheelbase, 3.55EL Rear End, 3566# Payload
    Adaptive Steering, Ultimate Camera Pkg, 20" Wheels, 397 Amp Dual Alternator, ARE Topper (Replaced 2004 F150)

  6. #6
    Left The Driveway
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    Quote Originally Posted by downsc123 View Post
    good write up - I have a very basic setup - just swapped the factory LA battery with a 100 Ah Li battery (left the camper converter alone as my solar charger can get the Li batter to 100 SOC). The only charging that I have from the truck is through the standard 7 pin cable. I assume I am ok as there is some current limiting device in the truck that would ensure I don't push too much current to the camper from the truck if I connect up and the Li camper battery is in a low state of charge - is my assumption good?
    Iím in the process of doing the same thing. 100Ah Li battery on its way. Hadnít thought there would be an issue with TV charging so looking forward to replies to this part of the topic.
    Jim & June
    2022 Transcend Xplor 200MK
    2021 Colorado Z71


  7. #7
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    Quote Originally Posted by JandJ_travels View Post
    I’m in the process of doing the same thing. 100Ah Li battery on its way. Hadn’t thought there would be an issue with TV charging so looking forward to replies to this part of the topic.
    If I'm following this question correctly, you are just trying to confirm that having a LFP battery connected to your trailer, while plugged into the tow vehicle's 7 pin connector will not cause any issues for the tow vehicle or camper/LFP battery? If that's the case, correct. The amount of charge coming through that 7 pin connector is measured in Milliamps. It will not damage the battery, alternator, or anything else. It will also provide very little charge to a LFP or LA battery regardless of level of charge remaining in the battery. Now, if you ran 4 gauge cables from the alternator back to a LFP battery without any type of regulator, that could make the alternator unhappy.
    Chad
    2023 23LDE 965W Solar, Victron Multiplus, Solar Controllers, Cerbo GX, 4x280AH DIY Lithium Batteries, SeeLevel Tank Monitoring, Shock Absorbers (Replaced 2022 22MLE)
    2022 F350 6.7L Superduty, Carbonized Gray, Ultimate Lariat Pkg, 4WD, Crew Cab, 160" Wheelbase, 3.55EL Rear End, 3566# Payload
    Adaptive Steering, Ultimate Camera Pkg, 20" Wheels, 397 Amp Dual Alternator, ARE Topper (Replaced 2004 F150)

  8. #8
    Fireside Member lineman1234's Avatar
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    I installed a gas transfer tank and gas rated electric transfer pump in my pickup bed. The pump needs power, i installed a 7 way plug to plug into one of the 2 seven way plugs and it powers the pump very well. So im not sure if the 7 way is just milliamps, as that pump needs amps.
    Also, on my cheby 3500 2024, the plugs are hot all the time. I am always in the habit of unplugging for an overnight stop, to not take the chance of draining the tow batt.
    Not sure if anyone has had problems with lithium on forgetting to unplug the 7 way overnight.

  9. #9
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    Always enjoy your write ups David! Lets see how this one gets turned into an EV discussion....lol...ooops...maybe me saying that is enough to do it...
    I think Riverbug is over-minimizing the 7 way. While he is right it is not super capable in stock form and won't charge the battery very fast, I get about 5-6 amps of charging current. It is, I think, a #12 awg wire. Maybe #14 ? So if it is #12 you can install a 20a DC-DC charger and charge up to 20a through the 7pin plug. If it is #14 you would need to restrict it to no more than 15a. This is the most economical way to get better charging, not necessarily the best way, but it is economical. Running a dedicated wire bypassing the 7 pin as David outlines gives you more options.
    Last edited by Scott'n'Wendy; 04-25-2024 at 05:48 AM.
    2018 Dodge 3500 6.7 Cummins SRW w/Aisin
    2021 Reflection 303RLS
    New to RV'ing since 1997

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    Quote Originally Posted by lineman1234 View Post
    I installed a gas transfer tank and gas rated electric transfer pump in my pickup bed. The pump needs power, i installed a 7 way plug to plug into one of the 2 seven way plugs and it powers the pump very well. So im not sure if the 7 way is just milliamps, as that pump needs amps.
    Also, on my cheby 3500 2024, the plugs are hot all the time. I am always in the habit of unplugging for an overnight stop, to not take the chance of draining the tow batt.
    Not sure if anyone has had problems with lithium on forgetting to unplug the 7 way overnight.
    Perhaps I'm thinking of my old truck, or maybe that old truck just had some issue after so many years. I haven't had a new model truck until recently but I haven't test that one yet. I'll have to check.
    Chad
    2023 23LDE 965W Solar, Victron Multiplus, Solar Controllers, Cerbo GX, 4x280AH DIY Lithium Batteries, SeeLevel Tank Monitoring, Shock Absorbers (Replaced 2022 22MLE)
    2022 F350 6.7L Superduty, Carbonized Gray, Ultimate Lariat Pkg, 4WD, Crew Cab, 160" Wheelbase, 3.55EL Rear End, 3566# Payload
    Adaptive Steering, Ultimate Camera Pkg, 20" Wheels, 397 Amp Dual Alternator, ARE Topper (Replaced 2004 F150)

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