Mastervolt DC-DC Converter Mac & Magic 24V

Yes. Modern vehicles (roughly Euro 5/6 onwards) use variable-voltage 'smart' alternators that swing anywhere from about 12.5V to over 15V to save fuel — which means your auxiliary or caravan battery sees too little voltage to charge properly most of the time. A DC-DC charger takes whatever the alternator gives it and outputs a correct multi-stage charge. And if the auxiliary battery is lithium, a DC-DC charger is essential regardless of alternator type: lithium connected directly can draw maximum current continuously and overheat the alternator. Simple rule: modern vehicle OR lithium auxiliary battery = DC-DC charger, no exceptions.

The same DC-DC rule as vehicles applies afloat: an outboard's charging circuit is unregulated and often modest (many outboards only make 6-15A of usable charge), and it must never be connected straight to a lithium house battery. A DC-DC charger between the start battery and the house battery converts whatever the engine provides into a correct multi-stage lithium (or AGM) charge, protects the outboard's charging system, and keeps the start battery isolated so you can always start the engine. Size it within the outboard's charging output — tell us your engine and house bank and we'll spec it.

Two limits set the size. (1) The battery: same minimum-10%-of-Ah rule as any charger — a 100Ah lithium suits 18-30A, a 200Ah bank suits 30-50A. (2) The alternator: keep the charger's draw comfortably inside its output — as a guide, no more than about half the alternator's rating, since the vehicle still needs power too. And the most common installation mistake, straight from the support inbox: undersized cable. A 30A charger at the back of a caravan on thin factory trailer wiring will starve, cut out, or fail to detect the engine — the run from the vehicle battery needs properly sized cable (often 6 B&S / 13mm2 or heavier for long runs). Our made-to-order cables cover exactly this.

Usually yes — and because lithium gives you 80-100% usable capacity versus roughly 50% for AGM, a 100Ah lithium replaces about 200Ah of AGM at a third of the weight. Three checks before you swap: (1) Every charge source needs a lithium profile — your 240V charger, MPPT and inverter/charger must be set (or settable) to a LiFePO4 program; old fixed-voltage chargers can't do it. (2) Alternator charging must go through a DC-DC charger — never connect an alternator straight to lithium. Lithium's very low internal resistance lets it pull maximum current continuously, which can cook an alternator, and modern smart alternators don't hold the right voltage anyway. (3) The BMS can disconnect the battery instantly to protect itself, so the system must tolerate that — another reason the DC-DC charger belongs in the circuit. We can check your exact setup from a photo of your battery compartment.

A CHARGER runs a proper multi-stage charging algorithm to charge a battery — that's what you want for an auxiliary or caravan battery. A CONVERTER outputs one fixed, stabilised voltage and exists to power equipment (for example running sensitive 12V electronics in a 24V truck). A converter is not a battery charger — its fixed voltage will never correctly charge, balance or protect a lithium battery.