Using 7-Way Trailer Connector 12-Volt Accessory Circuit to Maintain Battery on Dump Trailer

Question:

I have read your posts on charging the brake line or dump battery, including running a #10 wire from the 7 way harness 12V hot to the Positive terminal on the battery, but I am concerned about feedback when the trailer is off, or if the battery is too low to run the dump and it starts to pull from the truck battery. Should a fuse or circuit breaker be put in line? If so, how big? Also, the trailer has a brake battery as well. Does the order matter as to which battery gets plugged in to first? Thank you, as always.

asked by: Gary C

Expert Reply:

If you have read our previous responses regarding the use of the 12-volt accessory circuit from the 7-way, then you know that the circuit can be used to maintain, but not charge a depleted trailer-mounted battery. We typically recommend using a battery charger like the # CTEK56353 CTEK Universal Battery Charger to recharge a depleted battery.

The 12-volt accessory circuit should already be fused (or if the 7-way was installed aftermarket, protected by a 40 amp inline circuit breaker like part # 9510). Most dump trailers would use a battery large enough to provide the mandated 15 minutes trailer brake hold time, so typically an additional break-away battery would not be needed. If you decide to retain the separate break-away battery, you should splice an additional feed into the circuit, not chain one battery off of the other.

The small gauge of the wire from the 12-volt accessory circuit that limits the ability of the vehicle to charge the battery will also limit the amount of power pulled from the tow vehicle battery. If you are concerned about the trailer mounted battery depleting the tow vehicle battery when the tow vehicle is not running, you can install a battery isolator like part # PK5231201. The isolator will shut the accessory power circuit down when the vehicle ignition is turned off.

expert reply by: Mike L