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Adding AUX battery line to trailer

Discussion in 'Electrical' started by fotocamper, Jul 23, 2021.

  1. Jul 23, 2021 at 2:00 PM
    #1
    fotocamper

    fotocamper [OP] New Member

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    2016 Tundra Ltd 4x4 w/ towing package
    Bed cover, Firestone air bags
    Hi all,

    I'm putting more/better/bigger batteries on my travel trailer and to charge them from the truck I'm adding a DC-DC charger. But a 30A charger (to the battery) can require more like 44A on the input side when converter efficiency is factored in and the trailer batteries are low--way more than the 7-pin connector wire can provide. (I tried it and the voltage at the DC-DC chargers drops to 8.5V--not a safe condition and the 40A fuse will blow anyway.)

    So I'm going to add a pair of 6AWG wires from the truck battery to the back bumper where I will also add a connector to a trailer cable wired directly to the DC-DC charger. There will be a circuit breaker at the truck battery. The DC-DC charger already has engine running detection, but I may add a solenoid relay to power the trailer connector only when the ignition key is on.

    The question is, has anyone done this on their Tundra? (Mine is 2016 4x4 w/ tow.) I'm wondering about best cable path from the battery and then to the back of the truck. And also where to mount the circuit breaker--there's little room around the battery and fuse box. If you've attempted this, I'm interested in your experience!

    Thanks
     
  2. Aug 15, 2021 at 11:11 AM
    #2
    eick

    eick New Member

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    Circuit breaker fuse should be as close to the battery as possible. I’d run the wire down the frame rail if it were me but I’d try to attach it to existing wire bundles. Make sure you use loom or braided sheathing on the lines.

    If you don’t want to use the 7 pin for charging then you’ll need an additional connector. For that kind of amperage you can use an Anderson’s or you may be able to reuse the four pin if you don’t plan on ever using it.
     
  3. Aug 15, 2021 at 3:26 PM
    #3
    fotocamper

    fotocamper [OP] New Member

    Joined:
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    Messages:
    2
    Gender:
    Male
    Vehicle:
    2016 Tundra Ltd 4x4 w/ towing package
    Bed cover, Firestone air bags
    Thanks eick. I ended up starting in on this project about a week after my posting and did more or less exactly what you suggest.

    The breaker is in front of the battery, between the headlight and radiator. All the connections are hex crimped. From the battery, the wires are wrapped in a split woven loom sleeve for the rest of the run. I ended up running the cable across the top/front of the radiator (close fit with the hood) and then following OEM loom down to the frame rail and to the back of the truck. In the engine compartment I zip tied to solid mounts or where the loom was mounted. Under the truck I zip tied more frequently to the loom, about every foot or so. Terminated at an Anderson 50A connector under the rear bumper, supported by a gardner-bender type clamp. I'm not yet confident in the longevity of zip ties, but they are not exposed to UV so as soon as I see any deterioration in the engine compartment I'll replace them as needed.

    One thing I didn't anticipate is how much longer the wires need to be to run under, over and around things as I worked my way to the back of the truck. I pulled the wire under the truck from the back and through the engine compartment to get the length before cuttting. Then added the sleeve and started mounting from the battery to the back. This was something I haven't done before, so wiring both the truck and trailer took me what seems a long time, around 20-25hrs. I still want to get a solenoid in there, but I have to find the appropriate place to supply it with key-on power.
     
    cowboyjack likes this.

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