A DC-DC charger is effectively a smart-charger for your 12V system. It isolates the house battery system from the alternator, so that the vehicle’s computer management system sees it as something like a set of lights. At the same time, it boosts the charge at the house battery from as little as 9V back up to 14.4V (or higher, if required) to maximise charging capacity, delivering it in stepped form, like your smart mains charger, achieving close to 100 per cent charge after a day’s driving.
Most DC-DC chargers also act as solar regulators, relocating what’s traditionally been a separate item on your solar panel to a better position – adjacent to the house battery. And these are no ordinary regulators, but maximum power point trackers (MPPT) that optimise your solar panels’ performance.
Most DC-DC chargers draw a higher rate of amperage from the alternator than would be supplied if you let the alternator ‘push’ down the cable. This can be up to 40A or more per hour, quickly replenishing the house battery system.
Complete battery management systems (BMS) are new to the market and incorporate a mains charger, a DC-DC charger and MPPT solar regulator.
These generally come with a high-tech battery monitoring panel and, while expensive, are simple to install, requiring no post-manufacturer wiring between multiple units.
DC-DC chargers benefit from 6B&S/13.5mm² cabling (the conductor, not the conductor plus insulation, which is how most cable is sold). They work with smaller cable, but as the voltage drop through smaller cable increases, the heat produced reduces its conductivity, forcing the charger to work harder, drawing more current and increasing heat. This can continue to the point where the demand exceeds the alternator’s capacity to supply. The energy dissipates as heat is wasted.
Installing the charger near the house battery overcomes much of that voltage drop, while adhering to the manufacturer-recommended minimum clearance assists in dissipating heat.
DC-DC chargers increase the likelihood of your batteries arriving in camp at close to a full charge, minimises damage to your house battery system from over discharging and, in my opinion, should be fitted as mandatory or at least offered as an option on every camper and caravan sold in Australia.
Many factors can assist. Firstly, limit losses by:
using decent-sized cable from the alternator to the house battery (minimum 6B&S/13.5mm² – that’s close to a pencil in diameter) and replace any of the 6mm cable usually offered
using genuine Anderson plugs (not cheap clones, usually sold as ‘Anderson-style’ plugs)
crimping and soldering all connections.
Secondly, install a DC-DC charger adjacent to the house battery.
None of the units featured here were tested by us, as it would have demanded repeated wiring of the same battery system. We interpreted manufacturer-supplied figures and relied on the opinions of experienced installers.
When choosing a system, look for a good range of operating temperature, a good waterproof and dust (IP) rating, solar regulating capacity, adaptability to a wide range of battery chemistries and a wide range of input voltages.
The IP rating is a measure of a unit’s resistance to external intrusion, the higher the number the more resistant it is to the ingress of dust and water. The first number refers to dust, with 6 the highest standard, and the second to waterproofing, with 8 as fully submersible to 1m of water.