Parts Needed to Allow Tow Vehicle Battery to Charge Trailer Battery While Driving

Updated 08/04/2020 | Published 11/03/2013

Products Featured in This Question

Starter Solenoid - SPST - 12 Volt - 100 Amp - Continuous Duty - Grounded

(13)

$33.90

Ring Terminal - 12-10 Gauge Wire - 3/8" Ring ID

(69)

$1.67

Firestone Fuse Circuit Tap Kit

(39)

$20.98

Question:

I have a two wire +/- 12 volt plug at the rear of my truck to run power to my rear winch , it is wired directly to my truck battery with heavy gauge wire and a breaker. Can I use this connection to hook to my trailer battery and charge the trailer battery while driving. If so would I need to put something in the jumper line to prevent feed back from the trailer battery back to the truck. Thanks.

asked by: Tom

Helpful Expert Reply:

You may be able to use the existing 12V feed at the back of your truck to charge your trailer battery while driving but you will need to install a battery isolation solenoid to disconnect this line when the tow vehicle is off. Otherwise your trailer battery could drain the battery in the tow vehicle. You will also want to ensure that you are using a wire gauge heavy enough to pass the charging current to the trailer battery; 10-gauge would be the minimum.

You can use part # PK5231201 from TowReady. This isolation solenoid provides for an ignition controlled flow of current from your tow vehicle battery to the trailer battery. The solenoid will allow the 12V feed to remain active only when the vehicle is running; when the truck is turned off the 12V feed will also shut off. This will prevent battery drain in the truck but still allow charging of the trailer battery when the truck is running. The photo provided shows how this device connects. You will need ring terminals to connect, such as # DW05705-1.

You will need to use an ignition-controlled circuit in your truck to activate the solenoid. The radio circuit is often used for such purposes. You will need a fuse tap to access the switching function on this circuit; you can use part # F2526 from Firestone. This plugs into the fuse socket for your radio and connects to the center post on the solenoid. 12V power from the tow vehicle battery connects to either the left or right terminal and the power output exits the other side.

expert reply by: Adam R