Charging Trailer When Truck Engine Is Running

Question:

The 7 pin trailer pug is not large enough to charge my 4 six volt in series and parallel making 12 volts trailer batteries when I am driving. Can I connect the +12 volt line of this trailer plug to a battery disconnect solenoid and then run a separate and fused much larger gauge wire for both + and - from the truck battery/truck frame to the trailer battery without causing any problems? My 2018 gmc truck has 2 alternators with 200 amp charging capacity.

asked by: Richard

Expert Reply:

You're correct that the 12 volt power circuit from your truck will not effectively charge a trailer battery that is being used to power hungry electrical loads such as a fridge, lights, inverter, etc. The best way to charge a trailer battery is by using the Redarc In-Vehicle BCDC Battery Charger # 331-BCDC1225D (25A model) or # 331-BCDC1240D (40A model). These products also have an inbuilt MPPT solar regulator and battery isolator function. The solar regulator will allow you to charge the auxiliary battery simultaneously with charge from the vehicle's start battery or as a standalone regulator when the vehicle is not in use. The isolator function monitors the voltage of the vehicle's start battery and stops charging the auxiliary battery when it drops too low. This prevents a dead vehicle start battery.

The isolator function is automatic, meaning if you turned off your truck's ignition the trailer can stay connected to the truck without risk that the truck's start battery will go dead. Without this isolation feature the vehicle start battery will eventually go dead as it will continue to charge the auxiliary battery in the trailer.

40-Amp MIDI Fuse Kit for Redarc In-Vehicle 25-Amp BCDC Battery Charger is # 331-FK40 is available if you need additional fuses. Similarly, the 60-Amp MIDI Fuse Kit for Redarc In-Vehicle 40-Amp BCDC Battery Charger is # 331-FK60.

expert reply by: Timothy G