How to Prevent Battery Backfeeding and Breakaway Battery Charging Off Trailer Battery

Updated 11/12/2024 | Published 11/07/2024

Question:

Hello, I have an enclosed snowmobile trailer that has an onboard Power block where all of the trailer wires route and then power is distributed to the corresponding circuits blinkers, trailer lights, etc. I also have an onboard battery that runs the interior trailer lights. This battery is connected to the same circuit as the + power circuit from the vehicles 7 Pin. In addtion, my breakaway battery is connected to the same circuit. My issue is, with the onboard 12V battery connected to the trailer power block, I am getting back flow power to the + terminal on the trailer side of the harness/7 Pin at a full 12v with the battery connected and at about 1v with just the breakaway battery connected. At the same time the breakaway battery is charging off of the onboard battery when the trailer is disconnected from the car. I dont believe this is correct and that the break away should be separate from the 12V onboard battery. My issue is, how do I get the vehicle to charge both the onboard battery and the break away battery without them being on the same circuit and at the same time prevent power backflowing into the car? This is a facotry system but I wonder if somewhere along the line someone rewired the onboard battery and did it incorrectly. I appreciate any help you can provide. Thank you

asked by: David B

Expert Reply:

Hi David; this is pretty common and all you really need is to throw in some simple diodes # RM-690. These will only allow power to flow in one direction so it will stop any backfeeding and power drain. It sounds like everything is in-line so you can put one between the breakaway battery and your trailer battery and then one between the batteries and the tow vehicle.

expert reply by: Robin H

David B.

11/9/2024

Thank you! Since the (+) power from the car is running to a distribution pole on the trailer, can I just put one Diode on the supply line coming from the Car inside the trailer?

Robin H.

11/12/2024

@DavidB from what you described I believe you need two but it depends on how the wiring is set up. If you put one on the 12V power line before it gets to the junction box you may not be stopping the transfer of power between your trailer battery and breakaway. You probably need a 2nd one to keep these two from charging each other.