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  1. #1
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    Question Charge Primary Vehicle Battery through 7 Pin Tow Plug?

    Is it possible to trickle charge / maintain battery voltage through the 7 pin towing connector on a vehicle? I am not trying to charge a tow vehicle. I'm trying to charge the main battery through the 7 pin connector on the back as a convenient plug.

    I don't drive my 2006 Magnum SRT8 very much and would like to keep the battery from going flat.

    I also have this problem with my 2010 Dodge RAM 1500.

    Both vehicles have 7 pin trailer plugs, so it would be great if I could wire up a solar powered battery charger that would keep the batteries of these vehicles topped off.

    A simple magnetic break away cable would keep my wife from forgetting to disconnect and driving off damaging the equipment.

    Searches on this topic so far have only yielded people wanting to charge their tow vehicle with the lead vehicle. I am trying to charge the lead vehicle with something that is easily disconnected and reconnected. I do not have an outlet anywhere near where I park these vehicles.

    @fnkychkn can you see, without too much trouble, if these circuits are diode protected to prevent charging the main battery through these plugs?
    Did the radiator cap mod: SRT8 is here....
    The Hemi says, "VROOOM!" Hemi Registry #00420



  2. #2
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    I don't think there are any circuits hot all the time on the plug when the key is off, perhaps when the brake pedal is pressed but you don't want to back feed like that.



  3. #3
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    A 7 pin towing connector has a 12V hot and a ground wire.

    I am not talking about back feeding through a lighting circuit but rather trickle charging through the 12V+ and the GND wires.
    Did the radiator cap mod: SRT8 is here....
    The Hemi says, "VROOOM!" Hemi Registry #00420

  4. #4
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    I stand corrected thanks. Then it looks like you can do it. Just make up a pigtail.
    You will need to make sure it doesn't talk to your CANBUS and keep waking up your cluster DIC and such.
    I connected a radar detector (RD) to a circuit in the overhead console and experienced this. I cannot remember all the details but it had to do with if I setup the RD to auto on or not.

    Will be interested in how you make come out on this.



  5. #5
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    I put a solar panel suction cupped to the rear quarter window, ran the leads direct to the battery
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  6. #6
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    Quote Originally Posted by gapi View Post
    I stand corrected thanks. Then it looks like you can do it. Just make up a pigtail.
    You will need to make sure it doesn't talk to your CANBUS and keep waking up your cluster DIC and such.
    I connected a radar detector (RD) to a circuit in the overhead console and experienced this. I cannot remember all the details but it had to do with if I setup the RD to auto on or not.

    Will be interested in how you make come out on this.
    I've got some stuff on order. I'll give it a try.

    Quote Originally Posted by Warlock View Post
    I put a solar panel suction cupped to the rear quarter window, ran the leads direct to the battery
    Yeah, I wanted to avoid something that required opening the hood. Being able to charge from an external connector on the car / truck in this case would be preferred, for me. Glad you have a good solution though. I tried one of those solar panel trickle chargers and it was draining more power from my battery at night than it was creating during the day. (Cheap **** solar panels aren't diode protected... even decent diode protected ones can still cause a tiny bit of drain if they aren't disconnected from the circuit. I'm pretty sure the one I had was the cheapest garbage quality trickle charger available at the time. One of those: I should have bought a better one situations.)

    So I'm making my own now.
    Did the radiator cap mod: SRT8 is here....
    The Hemi says, "VROOOM!" Hemi Registry #00420

  7. #7
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    My trickle charger came with a cig lighter adapter, since the plug in the center console is hot I plug it in there, hard to drive away with the cord coming out the drivers door and only takes a second to plug/unplug
    2006 Charger SRT8

  8. #8
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    Quote Originally Posted by joekd View Post
    My trickle charger came with a cig lighter adapter, since the plug in the center console is hot I plug it in there, hard to drive away with the cord coming out the drivers door and only takes a second to plug/unplug

    Is your trickle charger plugged into an outlet? I don't have an outlet anywhere near where my 2 vehicles are parked. I need to trickle charge the batteries via a solar panel and charge controller that can do "float".

    Also, regarding: "Hard to drive away with the cord coming out the driver's door". For my truck, the cord would be coming out the passenger's door. My wife would absolutely drive away with it still connected.
    Did the radiator cap mod: SRT8 is here....
    The Hemi says, "VROOOM!" Hemi Registry #00420

  9. #9
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    Next time you're around any EVs, ambulances, fire trucks, etc. ask about their self ejecting plugs.
    My Charger was a county EMS vehicle, and had a hole in the quarter panel for one of these.
    Turning the key on activates a solenoid which pops the plug right out of the socket, might be possible to conceal one of these on your Ram, doubt you'd find a suitable spot on your Magnum.

  10. #10
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    Thank you very much for that term. I wasn't aware of solenoid ejecting plugs or self ejecting plugs. This gives me another thing to search for and look for. I have started to build up the solar powered battery charger but I haven't tested it on the 7 pin plug yet. I just need to plug it in one of these morning and make sure nothing catches fire.

    I'll do some searching for self ejecting plugs or auto ejecting plugs. Thanks again for that!
    Did the radiator cap mod: SRT8 is here....
    The Hemi says, "VROOOM!" Hemi Registry #00420

  11. #11
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    Hmm... maybe I should just add a weather proof 12V socket to the back of the car. A spring loaded cap that covers the socket to keep it clean, and a simple 12v dc power adapter that is wired to the battery through a fuse.

    Drive off and the plug should pull right out. I could create a spring loaded harness or a simple mechanism that directs the force properly. Easy to plug in. Keep it under the car and at an angle where water cannot collect in it at all...any condensation for example would run out and away (not that it would be a big issue, but trying to paint a mental image of the downward angle I would use.)

    Edit: Something like this (but hopefully a better quality version): Amazon.com: MMOBIEL Universal Waterproof 12V 120W Cigarette Lighter Power Plug Socket with Closing Cap incl Wiring Connection Kit
    Last edited by quarky42; 07-09-2020 at 06:05 PM.
    Did the radiator cap mod: SRT8 is here....
    The Hemi says, "VROOOM!" Hemi Registry #00420

  12. #12
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    B+ (pin 4 @ 1 o'clock) is unswitched and GND (pin 1 at 7 o'clock) when looking at the vehicle-side connector; they can be used to supply current to the battery (this is not a new thing). With vehicle off, you can easily confirm this with a DVM.

    Go buy a couple of cheap 7-way trailer connectors and connect the charger's red lead to the 7-way's red lead and the black charger lead to the 7-way's white lead (GND). Note that the series-resistance at this point of connection diminishes the effectivity of trickle charge devices - especially those that are constant current.

    Make doubly sure your chosen maintenance charger is NOT an archaic constant current device device (they hurt / kill lead acid batteries in short order).
    Last edited by Hemissary; 07-10-2020 at 08:54 PM.
    2005 Magnum RT---Viper Venom Red----440ci Aluminum block----Short Runner Valve Intake--410mm BAER 6S Monoblock Extreme--Eibach Multi-Pro 2

    Custom--Grille Work--Hood--Headlights--Side View Mirrors--Rear Spoiler--Rear Diffuser--SRV Control System--Turbine Wheels

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  13. #13
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    I have a medium quality charge controller for the solar panel. It isn't a constant current device and won't fry the battery over time.

    Thanks for the confirmation on the trailer connector

    I'd already bought the components and wired it up that way, but I want to add a break away so that if a certain significant other gets in the truck and doesn't disconnect the damn cable first, she doesn't do hundreds of dollars of damage to various components. I'm going to use a simple 12V socket and plug to accomplish this. I'll probably relay protect the plug so it is disconnected when there is no voltage coming from the charge controller. That should keep both parasitic drain at night to a minimum and help protect that port should it ever get pulled apart by force....

    It's either that or I hide the keys...
    Did the radiator cap mod: SRT8 is here....
    The Hemi says, "VROOOM!" Hemi Registry #00420

  14. #14
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    Quote Originally Posted by quarky42 View Post
    I have a medium quality charge controller for the solar panel. It isn't a constant current device and won't fry the battery over time.

    Thanks for the confirmation on the trailer connector

    I'd already bought the components and wired it up that way, but I want to add a break away so that if a certain significant other gets in the truck and doesn't disconnect the damn cable first, she doesn't do hundreds of dollars of damage to various components. I'm going to use a simple 12V socket and plug to accomplish this. I'll probably relay protect the plug so it is disconnected when there is no voltage coming from the charge controller. That should keep both parasitic drain at night to a minimum and help protect that port should it ever get pulled apart by force....

    It's either that or I hide the keys...
    Ah; forgot the solar aspect. The charge controller should already have discharge control circuitry. You can test this; simply measure resistance across the O/P leads of the controller when a) sitting on the bench (unconnected) and, b) in-circuit - night-time (this means any / all lights off as well).
    Last edited by Hemissary; 07-10-2020 at 02:21 AM.
    2005 Magnum RT---Viper Venom Red----440ci Aluminum block----Short Runner Valve Intake--410mm BAER 6S Monoblock Extreme--Eibach Multi-Pro 2

    Custom--Grille Work--Hood--Headlights--Side View Mirrors--Rear Spoiler--Rear Diffuser--SRV Control System--Turbine Wheels


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