Charging Trailer Battery From Tow Vehicle

Question:

How do you recommend charging a trailer battery be from an SUV tow vehicle alternator with out damage? What kind of isolation diode do you recommend to prevent discharging the tow vehicle starter battery? What kind of charge controller do you recommend to prevent overcharging the trailer battery?

asked by: Tony L

Expert Reply:

The circuit on the 7-way trailer connector can be used to maintain a trailer mounted battery, but the small diameter wire, the lack of output provided by the alternator and the long distance involved prevent enough power delivery to change a depleted battery. Your best bet is to use a battery charger like the CTEK # CTEK56353 to charge your battery when 120V AC power is available.

To prevent the trailer mounted battery from drawing on the vehicle battery when the tow vehicle is shut off, you'll first need to check if the 12-volt accessory power feed circuit on the 7-way is active when the vehicle is shut off. If it's a factory installed 7-way, it might power down when the ignition is turned off. You can use a circuit tester like part # PTW2993 to check the pin at the 1:00 position to see if it's active with the vehicle shut off.

If the circuit is live when the vehicle is turned off, you can install a battery isolating solenoid, part # PK5231201. The solenoid powers down the 7-way 12-volt accessory circuit when the vehicle is shut off.

expert reply by: Mike L