12V 40A DC-DC Battery Charger - Lithium and Lead-Acid, RV, Van, Marine

A DC-DC charger takes the messy, voltage-limited output of your vehicle's alternator and turns it into a proper charge profile for the house battery. This 40A unit is the middle of Rich Solar's three-model range and doubles as a battery isolator, so it replaces two components in a van or RV build.

Why this charger

• 40A output, 500W nominal, with a working range of 37-43A depending on conditions.
• Switchable battery chemistry: 12V AGM, flooded, gel and lithium, selected with a physical mode switch rather than buried in an app.
• Two-stage charging for lithium, which will safely reactivate an over-discharged LiFePO4 pack and take it to 100%. Three-stage for lead-acid.
• Works with both traditional and smart (variable-voltage) alternators, which is the whole reason a modern van build needs one of these.
• Built-in isolation prevents reverse current between the starter and house batteries, so a flat house bank cannot strand you.
• D+ ignition terminal means it only charges while the engine is running, protecting the starter battery.
• An LC low-current terminal lets you throttle it back for small or weak alternators instead of overloading them.
• Protected against over-voltage, over-temperature and reverse polarity. Standby draw is under 0.6A.

Be aware before you buy

• The D+ cable, the LC cable and the temperature sensor are not included. If you intend to use engine sensing, low-current mode or temperature compensation, budget for those separately.
• The RJ11 temperature sensor port compensates charge voltage for hot or cold conditions, but it is for lead-acid only — it does not apply to lithium.
• Efficiency is quoted as above 85% at 14VDC and 30% load. Manufacturers quote efficiency at their most flattering operating point; expect a little less at full output.

Choosing between 20A, 40A and 60A

• All three share the same feature set, the same 10-16VDC input window and the same charging logic. Only current, size and weight differ.
• 20A (250W) suits a modest 100Ah bank and a small alternator. 40A (500W) is the sensible default for a 200-300Ah lithium van build. 60A (750W) is for large banks and short drive times, but it demands an alternator that can actually supply it.
• Do not size up beyond what your alternator can deliver. A 60A charger on a tired factory alternator is a good way to cook the alternator.

Installation

• 10.3 x 7.4 x 3.1 inches and 4.9 lb. Mount in a ventilated space with the cooling surfaces clear.
• Input operating range is 10-16VDC.
• Cable and fusing must be sized for the full 40A on both the input and output side.

Warranty

• Covered by Rich Solar's standard limited warranty. No specific term is published on the product page; contact us to confirm the current coverage period.