Why Euro 6 Engines Changed Everything
If you own a motorhome or campervan built after 2014, there is a very good chance it has a Euro 6 compliant engine. Euro 6 engines use smart alternators that vary their output voltage to reduce fuel consumption and emissions. Unlike older fixed-output alternators that maintain a steady 14.4V, smart alternators frequently drop to 12.8V or lower, and sometimes switch off entirely when the engine management system decides the starter battery is charged.
This is a problem for leisure battery charging. Traditional split charge relays and voltage-sensing relays (VSRs) rely on detecting a voltage above approximately 13.3V to close the relay and connect the leisure battery to the alternator. With a smart alternator regularly sitting at 12.8V, the relay never triggers — or triggers so intermittently that the leisure battery barely charges at all.
Traditional Split Charge vs DC-DC Chargers
How Traditional Split Charge Works
A traditional split charge system uses a simple relay or VSR to connect the starter battery and leisure battery when the engine is running. When the alternator pushes voltage above the trigger threshold (typically 13.3V), the relay closes and current flows directly from the alternator to the leisure battery.
This approach has two key limitations with modern engines:
- Smart alternators defeat the trigger voltage — The relay may never close because the alternator voltage stays below 13.3V
- No charge profile control — Lead-acid and lithium batteries need specific charge profiles (bulk, absorption, float) that a simple relay cannot provide
- No current limiting — A flat lithium battery can draw enormous current through the relay, potentially overheating cables or tripping the alternator protection
How DC-DC Chargers Work
A DC-DC charger (also known as a battery-to-battery charger or B2B charger) sits between the starter battery and the leisure battery. It takes whatever voltage the smart alternator provides and boosts or regulates it to deliver the correct charge profile for your leisure battery type.
Key advantages of DC-DC chargers:
- Works with smart alternators — Accepts input voltages as low as 10.5V, so it charges regardless of alternator strategy
- Multi-stage charging — Delivers proper bulk, absorption, and float stages for optimal battery health
- Current limiting — Controls the charge current to protect cables, fuses, and the alternator
- Battery type selection — Configurable for lithium, AGM, gel, or flooded lead-acid batteries
- Temperature compensation — Optional temperature sensor adjusts charge voltage for battery temperature
The Victron Orion-Tr Smart Range
Victron's Orion-Tr Smart DC-DC chargers are the most popular choice for motorhome and campervan installations in the UK. The range includes models from 12A to 30A in both 12V and 24V configurations.
Available Models
| Model | Input | Output | Current | Best For |
|---|---|---|---|---|
| Orion-Tr Smart 12/12-18 | 12V | 12V | 18A | Campervans with moderate loads |
| Orion-Tr Smart 12/12-30 | 12V | 12V | 30A | Motorhomes and larger systems |
| Orion-Tr Smart 12/24-15 | 12V | 24V | 15A | 12V alternator to 24V battery bank |
| Orion-Tr Smart 24/12-20 | 24V | 12V | 20A | 24V trucks with 12V leisure system |
| Orion-Tr Smart 24/24-17 | 24V | 24V | 17A | 24V alternator to 24V battery bank |
Smart Features
All Orion-Tr Smart models include built-in Bluetooth for configuration and monitoring via the VictronConnect app. You can:
- Select the correct battery type (lithium, AGM, gel, flooded)
- Set custom charge voltages if needed
- Monitor real-time charge current and voltage
- Enable or disable the charger remotely
- View charge history and statistics
The charger also features an engine detection system that automatically starts charging when the engine is running and stops when it is switched off, without needing a separate ignition wire (though one can be used for more reliable detection).
The Victron Orion XS Range
Released in 2024 and expanded in 2025, the Orion XS is a significant step forward from the Orion-Tr Smart — delivering higher power, superior efficiency, and rugged IP65 weatherproofing in a smaller, lighter package. Both ranges are fully compatible with Euro 6 smart alternators.
Orion XS 12/12-50
The Orion XS 12/12-50 delivers up to 50A of charge current — 67% more than the largest Orion-Tr Smart — with notable engineering improvements throughout:
- 98% efficiency — Compared to approximately 87% for the Orion-Tr Smart. Heat output at full load is around 12W versus 50W, enabling installation in tight or poorly-ventilated spaces without thermal throttling.
- IP65 weatherproofing — Fully sealed against dust and water jets, making engine bay mounting practical and shortening cable runs to the starter battery.
- VE.Direct port — Wired connection to a Cerbo GX or Ekrano GX for DVCC coordinated charging and VRM remote monitoring, which is not possible with the Orion-Tr Smart over Bluetooth alone.
- Configurable output current — Adjustable from 0–50A via the VictronConnect app, allowing precise alternator load management suited to smaller or older alternators.
- Compact and lightweight — 191 × 67 × 38mm and just 0.5kg, approximately half the size and weight of the Orion-Tr Smart 30A.
Orion XS 1400
Available from July 2025, the Orion XS 1400 extends the range with 1,400W maximum output and multi-voltage flexibility — all from a single unit:
- Multi-voltage configuration — Operates as 12V→12V, 12V→24V, 24V→12V, or 24V→24V. A single unit replaces what previously required separate model variants.
- Up to 50A output across all voltage configurations at the full 1,400W rating.
- 98.5% efficiency using a re-engineered aluminium circuit board that acts as an integrated heatsink, eliminating the need for a cooling fan entirely.
- Full rated output to 40°C before any thermal derating — well-suited to summer touring and engine bay installation.
- IP65 rated, with VE.Direct port, Bluetooth, and full smart alternator detection identical to the XS 12/12-50.
Orion XS Available Models
| Model | Input | Output | Max Current | Power | Best For |
|---|---|---|---|---|---|
| Orion XS 12/12-50 | 12V | 12V | 50A | ~700W | New 12V builds, large lithium banks |
| Orion XS 1400 | 9–38V | 10–35V | 50A | 1,400W | Multi-voltage systems, maximum power output |
Orion XS vs Orion-Tr Smart: Which to Choose?
The Orion-Tr Smart remains a well-proven, cost-effective choice for moderate-capacity systems. The Orion XS is the better option when:
- You need more than 30A charge current — large lithium banks of 200Ah or more particularly benefit
- Mounting space is limited or engine bay installation is preferred
- Wired VE.Direct integration with a GX device and VRM remote monitoring is required
- The installation environment runs warm and minimising charger heat output matters
- You need 12V→24V or 24V→12V conversion without buying a dedicated separate model (XS 1400 only)
Sizing Your DC-DC Charger
Choosing the right amperage depends on your daily energy consumption and how long you typically drive:
Quick Sizing Guide
| Daily Usage | Typical Drive Time | Recommended |
|---|---|---|
| Up to 40Ah (500Wh) | 2+ hours | 18A charger |
| 40-80Ah (500-1000Wh) | 2-3 hours | 30A charger |
| 80-120Ah (1000-1500Wh) | 3+ hours | Orion XS 50A, or 2× 30A in parallel |
| Over 120Ah | Variable | 2× Orion XS 50A, or 50A + solar recommended |
The Orion-Tr Smart chargers can be wired in parallel for higher charge currents. Two 30A units give you 60A of charge capacity, which is ideal for larger lithium battery banks that can accept high charge rates.
Cable Sizing
Proper cable sizing is critical for DC-DC charger installations. The cable between the starter battery and the charger carries significant current. For a 30A charger on a 12V system, you need:
- Up to 3 metres: 10mm² cable minimum
- 3-5 metres: 16mm² cable recommended
- 5-7 metres: 25mm² cable recommended
Always install an appropriate fuse within 300mm of the starter battery. Use our Cable Sizing Guide tool to calculate the exact cable size for your installation.
Installation Considerations
Mounting Location
The Orion-Tr Smart generates heat during operation — a 30A unit at full output produces around 40W of heat. Mount it in a well-ventilated location, ideally on a vertical surface to allow natural convection. Avoid mounting in sealed compartments or directly above batteries.
The Orion XS range runs significantly cooler (around 12W at comparable outputs) thanks to its 98%+ efficiency, and its IP65 weatherproof rating means it can be mounted in the engine bay or other exposed locations without the same ventilation constraints.
Fusing
Install fuses on both the input (starter battery) and output (leisure battery) sides:
- Input fuse: 40A for the 30A model, 25A for the 18A model
- Output fuse: 40A for the 30A model, 25A for the 18A model
Use our Fuse Sizing Calculator to confirm the correct fuse ratings for your specific installation.
Integration with Solar
A DC-DC charger works alongside solar charging without conflict. The Victron Orion-Tr Smart and SmartSolar MPPT charge controllers can both charge the same battery bank simultaneously. The battery management system (BMS) in lithium batteries, or the battery's internal chemistry in lead-acid types, naturally manages the combined charge input.
Common Installation Mistakes
- Undersized cables — This is the most common issue. Voltage drop in thin cables reduces charge efficiency significantly
- Missing input fuse — The cable from the starter battery must be fused close to the battery for safety
- Poor ventilation — Mounting in a sealed space causes thermal throttling, reducing output current
- Wrong battery type setting — Charging a lithium battery with lead-acid settings (or vice versa) damages the battery or prevents full charging
- Ignoring alternator limits — Some smaller vehicles have alternators rated at only 90A. Adding a 30A DC-DC charger on top of normal vehicle loads may overwork the alternator in hot weather
Frequently Asked Questions
Can I keep my existing VSR alongside a DC-DC charger?
No. Remove the VSR or split charge relay when installing a DC-DC charger. Running both in parallel can cause charging conflicts and potentially damage the charger.
Will a DC-DC charger drain my starter battery?
The Orion-Tr Smart has built-in engine detection and a configurable low-voltage disconnect. It will stop charging if the starter battery voltage drops below a safe threshold (default 11.8V for 12V systems).
Do I need the non-isolated or isolated version?
For motorhome and campervan installations, the non-isolated Orion-Tr Smart is the correct choice. The isolated version is designed for specific applications where the battery grounds must be kept separate, such as some marine installations.
How long will it take to charge my leisure battery while driving?
A 30A charger at 12V delivers approximately 360W. For a 100Ah lithium battery discharged to 20% (80Ah to replace), it would take roughly 2.5-3 hours of driving. For a 200Ah bank, double that time or consider running two chargers in parallel.
Should I choose the Orion-Tr Smart or Orion XS?
Both work with Euro 6 vehicles. The Orion-Tr Smart is cost-effective and well-proven for systems requiring up to 30A. Choose the Orion XS if you need 50A charge capacity, IP65 weatherproofing for engine bay mounting, wired VE.Direct GX integration, or multi-voltage operation (XS 1400 only). For new builds with a sizeable lithium bank, the XS typically represents the better long-term investment despite the higher upfront cost.
Can the Orion XS 1400 charge a 24V battery from a 12V vehicle?
Yes. The Orion XS 1400 is configurable as a 12V→24V charger, delivering up to 25A into a 24V leisure battery bank (drawing approximately 50A from the 12V starter circuit). This replaces what previously required a dedicated Orion-Tr Smart 12/24-15 variant, while offering over 20% greater output power and the flexibility to switch voltage configuration in future should your system change.
