Short answer: size the charger so its amps are well under what your alternator and wiring can supply (20–60 A is common for vans), choose one with a LiFePO4 profile and smart/variable-voltage alternator support, and fuse both ends.
| If you need… | Look for |
|---|---|
| Small van, 100–200 Ah lithium | ~20–30 A charger |
| Bigger bank, long drives | ~40–60 A, if the alternator can handle it (check vehicle specs) |
| Want solar too, less wiring | Combined DC-DC + MPPT unit |
| Euro-6 / smart alternator vans | Charger that supports variable voltage and an ignition (D+) trigger |
Charge time: a 30 A charger adds about 30 Ah per hour of driving. Run the alternator-to-charger cable using the wire size calculator (runs are often 15–20 ft one way) and fuse it near the starter battery per the fuse guidance and the charger manual. Some chargers can't sit in hot engine bays; mount as instructed.
Safety: These are general estimates, not a design. Follow your equipment manufacturer's instructions and local electrical code, and consult a qualified electrician for anything connected to shore power, a house, or high-current batteries.
Usually yes: alternators often won't fully charge LiFePO4 and can be overloaded by a lithium bank's low resistance. A DC-DC charger controls the current.
Start around 20–30 A for small van systems; go larger only if your alternator and wiring support it.
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