DC to DC Charger.
Image from whichcar.com.au

Originally, motorhome house batteries could be charged directly from the vehicle's primary alternator using a system that connects the house battery to the alternator called a Voltage Sensitive Relay. The problem is that alternators usually only achieve about 50-75 percent charge state. With the introduction of new smart alternators we can now get a charge that is closer to 100. The only problem is that Smart alternators output voltage can vary considerably and does not always suit deep cycle house batteries. If the voltage is too low it will not charge efficiently. If it is too high, you run the risk of causing damage. VSRs will turn off when the voltage is too low or too high. That’s when DC to DC chargers come into play.

DC to DC Charger

A DC to DC charger is a great to have for any 12V battery power system. A DC to DC battery charger works by isolating the main 12V battery system from the alternator. The smart alternator computer management system then reads it as an object using power, rather than a battery. This boosts the charge at the main battery and maximises the charging capacity. 

DC-DC chargers can handle a high or low alternator output and modify it to the required voltage of the battery being charged. This system can charge up to 5 times quicker than a Voltage Sensitive Relay system. They are connected between the starter battery and the house battery and are programmed for battery type.

When to use a DC to DC charger

You should first test the voltage output of your vehicle's alternator to see if you need one. DC-DC chargers can be helpful but they can also be less than helpful if they don’t meet the requirements. If you’re unsure about whether you may need one, here is a technical guide to finding out.


Here are a few from our range: