The essentials in 30 seconds
- 4 key applications: (1) alternator protection for power-hungry lithium banks, (2) 12↔24 V conversion for mixed equipment, (3) smart charging of starter batteries from house bank, (4) remote power supply for displays/PCs with stable voltage.
- Isolated vs non-isolated: isolated = separate ground between input/output, essential for mixing 12 V banks or having a clean ground reference. Non-isolated = simpler and cheaper, OK when both sides share the same ground.
- 2026 standards: Victron Orion XS 1400 (~ 350 € VAT excluded) for lithium alternator protection. Orion-Tr Smart 12/12-18A isolated (~ 171 € VAT excluded) for standard uses.
- Sizing = max current + 30%. 30 A continuous output → converter 40 A minimum to avoid saturation and shutdowns.
- Typical refit budget: 200-600 € VAT excluded for DC-DC + wiring + protection. Huge difference in battery bank longevity and electrical system reliability.
The DC-DC converter is the least glamorous piece of equipment on a sailboat — and one of the most critical for electrical reliability. On a modern refit with lithium house bank + lead starter + 24 V propulsion, there are 2 to 5 units. Poorly chosen, they cause invisible intermittent faults. Properly sized, they run the entire system for 10-15 years without intervention.
This article details the 4 key applications, Victron and Mastervolt ranges stocked at Skysat, and provides installation guidelines. For the lithium bank they protect, see switching to lithium.
4 key applications of DC-DC for sailboats
1. Alternator protection for lithium house bank
Lithium demands 100 A from an 80 A alternator → overheating and failure. The DC-DC limits the current drawn to a safe value (30-40 A typical). See our plug & play lithium article.
2. 12 ↔ 24 V conversion for mixed equipment
Yacht running 24 V but with 12 V equipment (standard fridge, N2K displays, USB) or vice versa. The DC-DC converts voltage with 90-94% efficiency.
3. Smart charging of starter battery from house bank
Lead starter battery kept charged by the lithium house bank via DC-DC. Avoids the need for a dedicated shore charger for the starter battery.
4. Remote power supply for displays/PCs
Bus voltage varies 11-15 V depending on load. Sensitive displays prefer 12.5 V stable. Isolated DC-DC provides this stability.
Isolated vs non-isolated — selection rules
- Isolated: separate ground between input/output. Benefit: no ground current between circuits, elimination of electrical noise, protection against ground loops. ~30-50% surcharge vs non-isolated.
- Non-isolated: common ground. Simplicity and lower cost. Suitable when both sides share the same ground reference (standard pleasure craft with single negative battery ground).
Practical rule: use isolated for voltage conversions between circuits (12→24 V, 24→12 V), non-isolated for alternator protection or charging between batteries at the same voltage.
Victron Orion range
Flagship DC-DC range for pleasure craft, from entry-level at 100-150 € VAT excluded up to XS 1400 at ~ 350 € VAT excluded.
- Orion-Tr Smart 12/12-30A non-isolated (~ 230 € VAT excluded): battery-to-battery charging without isolation. For maintaining starter battery from house bank.
- Orion-Tr Smart 12/12-18A isolated (~ 171 € VAT excluded): isolated version at the same voltage. For clean DC bus powering remote displays or PCs.
- Orion-Tr Smart 24/12-20A isolated (~ 171 € VAT excluded): 24→12 V conversion for N2K equipment and fridge on 24 V yachts.
- Orion-Tr Smart 24/24-17A: stabilized DC bus on 24 V yachts.
- Orion XS 1400 (~ 350 € VAT excluded): 50 A continuous, designed for alternator protection of large lithium banks. Our 2026 workshop standard for lithium refits.
Mastervolt DC Master range
Direct competitor to Victron, MasterBus integration for CZone-equipped yachts.
- DC Master 12/12-6 isolated (~ 220 € VAT excluded): basic conversion for ECUs and sensitive electronics.
- DC Master 48/12-20 (~ 365 € VAT excluded): 48→12 V conversion for yachts with electric propulsion and 48 V house bank.
Mastervolt is justified on new Bénéteau/Jeanneau yachts equipped with CZone (native dashboard integration); Victron for everything else.
Current and voltage sizing
- Identify max downstream load. 4 A display + 6 A autopilot + 3 A continuous fridge = 13 A continuous.
- Add 30% safety margin for peaks. 13 × 1.3 = 17 A.
- Select DC-DC with nominal current ≥ 17 A. Orion-Tr Smart 12/12-18A (18 A nominal) or higher.
- Check efficiency. 90-94% on modern Orions. For 18 A at 12 V = 216 W output, 240 W input → ~24 W dissipated as heat (to be ventilated).
2026 model comparison chart
| Model | Type | Voltage | Max current | Isolated | Price VAT excluded |
|---|---|---|---|---|---|
| Orion-Tr Smart 12/12-18A | Stabilized bus | 12→12 V | 18 A | Yes | ~ 171 € |
| Orion-Tr Smart 12/12-30A | Battery charging | 12→12 V | 30 A | No | ~ 230 € |
| Orion-Tr Smart 24/12-20A | Conversion | 24→12 V | 20 A | Yes | ~ 171 € |
| Orion-Tr Smart 24/24-17A | Stabilized bus | 24→24 V | 17 A | Yes | ~ 220 € |
| Orion XS 1400 | Alternator protection | 12→12 V | 50 A | No | ~ 350 € |
| DC Master 12/12-6 isolated | Sensitive conversion | 12→12 V | 6 A | Yes | ~ 220 € |
| DC Master 48/12-20 | High-power conversion | 48→12 V | 20 A | Yes | ~ 365 € |
Workshop installation — wiring and protection
Skysat workshop rules
- Input and output cables sized for max current + 30%. Orion 30 A → 6 mm² minimum cable.
- Class T or MEGA fuse in series on input. Rated at 1.2× nominal current.
- Mandatory ventilation. Heat dissipation 10-30 W depending on model. Not to be installed in a closed locker.
- Position close to the supply battery. Short input cable = less loss.
- VictronConnect programming. Set output voltage, max current, and specific charge profile according to use. Must be configured at commissioning.
FAQ — DC-DC in practice
How many DC-DC units on a typical 40-foot sailboat?
2-4 units: (1) Orion XS alternator protection, (2) Orion-Tr 12/12 for stabilized display bus, (3) Orion-Tr 12/12 for starter battery maintenance if lithium house bank, (4) optional 24/12 if partial 24 V system.
Does DC-DC make noise?
Very little in practice. Fan on models ≥ 30 A may be audible (40-50 dB) nearby. Models ≤ 20 A are silent (passive heatsink).
Is Bluetooth Smart useful?
Yes for monitoring: voltage, current, temperature, history via VictronConnect. Allows remote detection of faults. ~50-80 € surcharge, cost-effective after first avoided service call.
Difference between Orion Tr Smart and Orion XS?
Tr Smart = entry/mid-range, designed for stabilized bus and conversion. XS = high-power, designed for lithium alternator protection (50 A continuous). Choose based on application.
Can DC-DC units be paralleled for more power?
Technically possible but not recommended without load-sharing. Better to choose a larger model directly.
3 real-world workshop cases — DC-DC installations
Case 1 — Bénéteau Oceanis 38 lithium conversion
200 Ah lithium house bank + original 80 A alternator. Alternator protection via Orion XS 1400 (~ 350 € VAT excluded) limiting current to 50 A continuous. Preserves alternator under full lithium load. Total install: 450 € VAT excluded (DC-DC + wiring + 200 A class T fuse).
Case 2 — Bavaria 50 24 V yacht with 12 V fridge
2018 24 V yacht but Vitrifrigo C115 12 V fridge (Danfoss BD35 compressor). Solution: Orion-Tr Smart 24/12-20A isolated (~ 171 € VAT excluded) dedicated to fridge. Stable conversion, correct fridge cycling, 24 V consumption measured 4-5 A.
Case 3 — 38-foot sailboat — stabilized DC bus for displays
Multiple displays + sensitive on-board computer affected by voltage variations (raw 11-14.5 V while sailing). Installed Orion-Tr Smart 12/12-18A isolated (~ 171 € VAT excluded) with stable 12.8 V output. No more display reboots in 18 months.
Excluded alternatives — DC-DC not recommended
- Low-cost Chinese DC-DC (40-80 € VAT excluded): avoid. Advertised efficiency often 95% but real-world 80-85%, poor thermal management, possible short-circuit under overload. For 100 € difference, choose Victron or Mastervolt.
- Automotive-grade Camp Sport DC-DC (high-end): excellent for motorhomes but insufficient marine rating (IP20 enclosure). In marine humidity, lifespan 2-3 years vs 10+ years for Orion marine models.
- DIY DC-DC with discrete components: fun electronics project but no marine certification, no warranty. Avoid for real sailboat installations.
Orion programming via VictronConnect — key parameters
Once Orion is installed, program via VictronConnect app (Bluetooth Smart included on all Smart models):
- Minimum input voltage: set to 11.8 V (12 V lithium bank) to avoid deep discharge.
- Output voltage: 12.8 V stable for display bus, 14.4 V for lead starter battery charging.
- Maximum current: set according to input cable (safety). For 35 mm² cable, limit to 100 A.
- Mode: "ON/OFF" simple or "ON via Engine Sense" (activates only when engine runs and alternator is charging).
Skysat distributes Victron Energy and Mastervolt. 2026 VAT-excluded prices are indicative distributor pricing.
