Charging your batteries can come from 3 sources – solar, AC charging when connected to shore power, and DC-DC charging from the tow vehicle alternator when towing. Note that DC-DC charging and solar charging can happen simultaneously when towing.
It is vital that both AC and DC-DC chargers have the correct charging profile for the RV battery type – an incorrect charging profile can potentially diminish battery life and incomplete charging.
Connecting an AC charger is generally straight forward, with the charger capacity being matched to battery capacity. The charger should be located as close to the batteries as possible.
Connecting a DC-DC charger to the tow vehicle alternator is more complex due to the generally long distance from alternator to RV batteries. Connection at the drawbar on a caravan is by way of Anderson plugs. Cable sizing must be sufficient to minimise voltage drop in the cables under the high current, and the connection to the alternator must be fused. In addition, to avoid draining the tow vehicle battery, the system must be configured to only draw current when the tow vehicle engine is running. Again the charger capacity will be closely matched to battery capacity, and the charger should be located as close to the RV batteries as possible.
A DC-DC charger also becomes an excellent back-up charger when parked off grid for a long period of time in inclement weather. To recharge the batteries quickly, just plug in the Anderson plug to the tow vehicle and idle the tow vehicle engine for an hour or two. Most diesel engines will only use around 1L/hr at idle, so this is economical and saves the weight and space of carrying a generator.
