A DC-DC charger lets your alternator safely charge your lithium house battery while you drive. The Victron Orion-Tr Smart sits between the starter battery and the house bank, taking variable alternator voltage and delivering a correct multi-stage charge. Wiring it means a fused input from the starter side, a fused output to the house battery, a shared ground, and an engine-detection method. This guide walks the install and the VictronConnect setup.
Why you need a DC-DC charger for lithium
Connecting a lithium house battery straight to the alternator can over-work the alternator and won't fully charge the lithium. A DC-DC charger limits current to a safe level and applies the right lithium charge profile — so you get reliable charging on the move without cooking the alternator.
What you'll need
- Victron Orion-Tr Smart DC-DC charger, sized to your alternator and battery (18A and 30A are common RV sizes) — shop DC-DC converters
- Cable sized to the charger's current, plus a fuse on both the input and output — see fuses
- Lugs, crimp tool, and (for non-smart-alternator vehicles) an ignition/D+ wire or the engine-detection setting
Step 1 — Mount the charger
Mount the Orion in a ventilated spot, ideally between the starter and house batteries to keep cable runs short. Keep it dry and allow airflow — DC-DC chargers generate heat under load.
Step 2 — Wire the input (starter side)
- Run a fused cable from the starter battery positive (or a suitable feed) to the Orion's input positive.
- Place the input fuse close to the starter battery.
- Size the input cable for the charger's input current, which is higher than its output rating.
Step 3 — Wire the output (house side)
- Run a fused cable from the Orion's output positive to the house battery positive.
- Place the output fuse close to the house battery.
Step 4 — Ground & engine detection
- Connect the Orion's input and output negatives to a common ground/negative bus.
- Engine detection: either enable voltage-based engine detection in VictronConnect (it starts charging when it senses the alternator), or wire the remote H/L terminal to a switched ignition/D+ source so it only runs with the engine on.
Step 5 — Configure in VictronConnect
- Connect over Bluetooth and set the output battery type/profile (e.g. LiFePO4).
- Set or confirm the engine-detection method and input voltage lockout.
- Start the engine and confirm the Orion is charging the house battery.
Pairing it with solar and shore charging? See how to size your lithium bank and build a Victron off-grid power system.
Common mistakes to avoid
- Undersized input cable — input current exceeds output current; size for the input.
- Fuses too far from each battery — fuse both ends close to their battery.
- No engine detection on a smart alternator — set the right mode or it may charge at the wrong time or not at all.
- Wrong output profile — set the lithium profile so the bank charges fully and safely.
Frequently asked questions
What size Orion DC-DC charger do I need?
Match it to your alternator capacity and how fast you want to charge — 18A suits smaller setups, 30A is a common all-rounder. Don't exceed what your alternator can spare.
Do I need a DC-DC charger for lithium?
Yes, in nearly all cases — it protects the alternator and applies the correct lithium charge profile that a direct connection can't.
Does it charge while parked?
No — it charges from the alternator while the engine runs. Use solar or shore power to charge while parked.
Can I run solar and the DC-DC charger together?
Yes. The MPPT and DC-DC charger can both feed the house battery; with a Cerbo GX they coordinate via DVCC.
Charge while you drive: Shop Victron Orion DC-DC chargers — in stock, ships from Upland, CA.