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  1. #1
    Seasoned Camper
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    How does the truck charge the trailer battery?

    My truck is not charging the trailer battery when I'm driving.

    I know the power comes to the trailer via the 7 pin cable and I've confirmed that power is present on the correct pin in the connector. So I'm assuming that there is a problem somewhere in the RV. Does anyone know how this is wired in the trailer?

    Sometimes when we arrive at the campground the battery charge indicator will have dropped from the normal 100% down to 90% (we have a Go Power Solar Elite system which shows the state of charge). I've ignored this until now since it didn't cause any problems. But recently we have tried using the inverter to run the refrigerator and the charge level drops significantly, so it is time to fix this.

    I'm sure the information is here somewhere, but I can't find it.

    Any help will be appreciated.
    John & Cheryl
    Sold: 2017 Tiffin Allegro 31SA Motorhome
    Sold: 2017 Reflection 337RLS, dual pane windows, 2nd A/C, Go Power! Solar Elite w/2000 watt inverter, Titan electric/hydraulic brakes, Goodyear Endurance ST235/85 R16 tires
    Sold: 2015 Chevy Silverado LTZ 3500HD, SRW, Duramax/Allison, 50 gallon Transfer Flow auxiliary tank
    States we have camped in with an RV:

  2. #2
    Fireside Member BC315RLTS's Avatar
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    Have you set the trailer up in the towing screen? Sometimes if the trailer isn't created, the battery charging will not work.
    2019 Reflection 315RLTS
    2019 Ford F250 Lariat SuperCab PSD SRW

    Former set up:
    2013 Kodiak 291RESL
    2017 Ford F150 Platinum

  3. #3
    Seasoned Camper
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    Hi,

    Not sure what you mean. As I mentioned, power is present on the connector.
    John & Cheryl
    Sold: 2017 Tiffin Allegro 31SA Motorhome
    Sold: 2017 Reflection 337RLS, dual pane windows, 2nd A/C, Go Power! Solar Elite w/2000 watt inverter, Titan electric/hydraulic brakes, Goodyear Endurance ST235/85 R16 tires
    Sold: 2015 Chevy Silverado LTZ 3500HD, SRW, Duramax/Allison, 50 gallon Transfer Flow auxiliary tank
    States we have camped in with an RV:

  4. #4
    Site Sponsor
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    Anything running on 12V in the trailer? There isn’t a lot of charging current available from the truck.
    John & Kathy
    2014 F250 Lariat FX4 6.2L SBCC
    2014 Reflection 303RLS
    SW Indiana

  5. #5
    Seasoned Camper
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    Nothing other than the stuff that is always on, other than the refrigerator. On propane the charge will drop from 100% to 90% in a couple of hours of driving.

    I'm suspicious that when the solar was added something was messed up. I want to trace the wiring from the 7 pin cable but am not sure where it should go.
    John & Cheryl
    Sold: 2017 Tiffin Allegro 31SA Motorhome
    Sold: 2017 Reflection 337RLS, dual pane windows, 2nd A/C, Go Power! Solar Elite w/2000 watt inverter, Titan electric/hydraulic brakes, Goodyear Endurance ST235/85 R16 tires
    Sold: 2015 Chevy Silverado LTZ 3500HD, SRW, Duramax/Allison, 50 gallon Transfer Flow auxiliary tank
    States we have camped in with an RV:

  6. #6
    Long Hauler
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    Up where the pin box connects to the frame of the trailer there is a silver metal box , this is where the pigtail that plugs into the truck is connected to the trailer. Check here for your hot wire coming from the truck, should be a red wire. If you have power here check behind the breakers on the wall beside the battery there should be a red wire coming from the silver metal box back to these breakers that should be connected to the battery for charging. If you plug the truck in and un hook the battery in the camper you should be able to find the red wire at the breakers if it is hooked correctly in the silver box. Just make sure you have no power at the breakers before testing this.

    Brian

  7. #7
    Site Sponsor
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    This is so funny! I asked almost the exact same question on a different forum earlier today.

    This is the one suggestion I got...

    "Disconnect the 12v wire connecting your tow vehicle to the trailer and see if this continues. If it stops then just leave it that way and let the Solar Panels keep the trailer batteries charged. That's the only function of that wire.

    I found that same phenomena after installing my Battleborn LiFePo batteries. When they were fully charged they actually discharged back into my tow vehicle because of the voltage differences between FLA and LiFePo batteries.

    I solved it by installing a Renogy DC-DC 20 amp charger in my TT that is connected directly to the 12 v "Charge Wire" from my TV. It acts as a battery isolator as well as charging the LiFePo's at their higher charge voltage. $127 and a couple hours of install/wiring. Well worth it according to babcock it's a good idea for charging regular FLA batteries, especially if the TV has one of the modern variable output alternators."


    I don't know if that will help, but I figure it's worth a try.

    Eric
    Last edited by DaTraveler; 06-10-2019 at 07:24 PM.

  8. #8
    Seasoned Camper
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    Quote Originally Posted by Country Campers View Post
    Up where the pin box connects to the frame of the trailer there is a silver metal box , this is where the pigtail that plugs into the truck is connected to the trailer. Check here for your hot wire coming from the truck, should be a red wire. If you have power here check behind the breakers on the wall beside the battery there should be a red wire coming from the silver metal box back to these breakers that should be connected to the battery for charging. If you plug the truck in and un hook the battery in the camper you should be able to find the red wire at the breakers if it is hooked correctly in the silver box. Just make sure you have no power at the breakers before testing this.

    Brian
    So does the red wire from the truck just go directly to a battery terminal? Or does it go through some electronics to regulate the charging?
    John & Cheryl
    Sold: 2017 Tiffin Allegro 31SA Motorhome
    Sold: 2017 Reflection 337RLS, dual pane windows, 2nd A/C, Go Power! Solar Elite w/2000 watt inverter, Titan electric/hydraulic brakes, Goodyear Endurance ST235/85 R16 tires
    Sold: 2015 Chevy Silverado LTZ 3500HD, SRW, Duramax/Allison, 50 gallon Transfer Flow auxiliary tank
    States we have camped in with an RV:

  9. #9
    Site Sponsor gbkims's Avatar
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    Click image for larger version. 

Name:	317RST Pin Box Junction Box.pdf 
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    Quote Originally Posted by SmallBoxMaker View Post
    So does the red wire from the truck just go directly to a battery terminal? Or does it go through some electronics to regulate the charging?
    Straight to the +12V in the trailer, usually at the auto resetting circuit breakers.
    My pin box junction box wires were connected to the 7-pin cable like this.
    Just a couple differences on where they end up in the trailer now.
    - Gene

    Kim & Gene
    2015 Reflection 317RST
    2017 Ram 3500 CC LB 4x2 6.7 CTD AISIN 3.73 DRW Auto Level Rear Air, BD3, Prodigy P3, Aux Tank

  10. #10
    Seasoned Camper
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    Thanks for the ideas and sorry for the delay getting back.

    I've confirmed that power from the truck is getting to the battery, so the problem is somewhere else. So much for it being simple.

    The test I ran was to disconnect the battery, solar and unplugged from shore power. As expected, no lights were on in the rig. I plugged into the truck and the lights came on.

    Not sure where to look next.
    John & Cheryl
    Sold: 2017 Tiffin Allegro 31SA Motorhome
    Sold: 2017 Reflection 337RLS, dual pane windows, 2nd A/C, Go Power! Solar Elite w/2000 watt inverter, Titan electric/hydraulic brakes, Goodyear Endurance ST235/85 R16 tires
    Sold: 2015 Chevy Silverado LTZ 3500HD, SRW, Duramax/Allison, 50 gallon Transfer Flow auxiliary tank
    States we have camped in with an RV:

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