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How to Wire Trailer Winch Battery Without Risking Depletion of Tow Vehicle Battery


I am installing a battery on my trailer for winch and I have no problem with charging battery with 120v charger before each tow but I was thinking on the idea of hooking up to the 12v circuit on the 7 pin connector to keep the battery maintained but being around vehicles alot I see many bad batteries which will burn up alternators and can draw as many amps as the alternator will produce. Can my 7 pin wiring on my 2010 f150 withstand a battery if it goes bad while towing and starts drawing max amps from alternator. Maybe I should use a larger cable and run all the way to truck battery but that still does not eliminate the possibility of overloading charging system if trailer battery goes bad even though truck battery could also do the same. Im just trying to figure out how to eliminate added maintenance. If I use the 7pin connection is there any type of device I can install which will go open circuit if trailer battery started drawing too many amps?


Expert Reply:

The 12V power feed from a tow vehicle's 7-way connection passes enough current maintain a battery but not enough to charge a depleted one. Shore power and a 120V charger such as what you have is the right way to charge a discharged battery.

You can isolate your tow vehicle battery (and alternator) from power draw from the trailer battery by installing an isolation solenoid, part # TR118665. This item uses any ignition-controlled circuit in the vehicle, such as the radio or power antenna, to open and close the solenoid. The center terminal takes in the ignition-switched signal and turns on and off the 12V power passing through the solenoid. Please refer to the linked photo.

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