The Victron Buck-Boost DC-DC converter charges a 12V or 24V service battery from a vehicle with a smart alternator. It can step voltage up (boost) or down (buck), so the house battery gets a set charge voltage whether the alternator is running low or high. Victron’s datasheet gives Mercedes’ 15.4V as an example of a high one. Here’s what the 25A, 50A and 100A models offer.
Victron Buck-Boost DC-DC: Specs
| 25A | 50A | 100A | |
|---|---|---|---|
| Input voltage range | 10–30V | 10–30V | 10–30V |
| Output voltage range | 10–30V | 10–30V | 10–30V |
| Max charge current, 12V | 25A | 50A | 100A |
| Max charge current, 24V | 15A | 25A | 50A |
| CAN bus activation | No | Yes | Yes |
| Weight | 0.6kg | 1.4kg | 4.1kg |
| Size (mm) | 165 × 120 × 30 | 213 × 120 × 30 | 288 × 162 × 95 |
Source: Victron Buck-Boost DC-DC Converter 25A/50A/100A datasheet.
Power-save mode draws 7mA. The undervoltage threshold is 10V, and the converter is rated for -25 to +60°C.
Features
- Any 12/24V combination: 12V to 12V, 12V to 24V, 24V to 12V or 24V to 24V, set in software.
- Engine-running detection to avoid draining the starter battery. You can also trigger it from D+, CAN bus (not on the 25A) or a (+)15 ignition signal.
- Charge-current and input-current limits, plus a temperature limit, to protect the alternator and wiring.
- Input and output status LEDs that show engine detection, low input voltage, over-temperature and battery state.
Programming
The Buck-Boost is set up with a PC application over a USB A-to-B cable, according to Victron’s datasheet. It doesn’t list Bluetooth or VictronConnect support, which is the main practical difference from the newer Orion chargers.
Buck-Boost vs Orion XS and Orion-Tr Smart
| Buck-Boost | Orion XS / Orion-Tr Smart | |
|---|---|---|
| Setup | PC software over USB | Bluetooth, VictronConnect |
| Top current | 100A (12V) | Up to 70A (Orion XS 12/12-70A), 30A (Orion-Tr) |
| Current setting | Charge and input current limits | Input and output current setting (XS) |
Who It’s For
- Vans and trucks with smart alternators that need high charge current, using the 50A and 100A models.
- Mixed-voltage vehicles, such as a 24V truck with a 12V house battery.
- Fleet installs where settings are programmed once on a PC.
Good to Know Before You Buy
- No Bluetooth or app monitoring.
- The 100A model is large, at 4.1kg.
- The 25A model has no CAN bus input.
Want the source figures? The Buck-Boost DC-DC converter page on Victron’s site has the datasheet.
Worked Example: A Mercedes Sprinter With a High Alternator Voltage
Victron’s datasheet mentions 15.4V from some Mercedes alternators. Connecting a 12V lithium house battery straight to that would push it above its charge voltage. The Buck-Boost steps that 15.4V down to a set charge voltage, for example 14.2V for LiFePO4 (example setting; use your battery’s datasheet). When the alternator later drops to 12.5V under smart control, the converter boosts it back up, so the battery keeps charging.
Worked Example: Charge Time on the 50A Model
A 12V 300Ah lithium house bank at 30% (about 210Ah to replace):
- 50A model: about 4.2 hours of driving in bulk (estimate).
- 100A model: about 2.1 hours (estimate), but check the alternator can supply roughly 110A or more on top of the vehicle’s own loads.
- Input-current limit: setting it to, say, 60A on a 150A alternator keeps margin for the vehicle’s systems (example).
Worked Example: 24V Truck to 12V Camper
A 24V truck charging a 12V camper battery: the 50A model supplies up to 50A at 12V output. From the 24V side, that’s about 25–30A of input current, depending on efficiency (estimate). That’s easy on a typical truck alternator.
Triggering Options Compared
| Trigger | When to use it |
|---|---|
| Engine-running detection (voltage) | Simple installs with a conventional alternator |
| D+ signal | Vehicles with a D+ terminal on the alternator or fuse box |
| (+)15 ignition signal | Smart alternators whose voltage varies while driving |
| CAN bus (50A and 100A) | Vehicles where the converter can read engine status from the CAN network |
Installation Steps
- Mount on a vertical surface in a ventilated spot, away from heat sources.
- Run cables from the starter battery and to the house battery, sized for the maximum current; use the shortest practical runs.
- Fit fuses close to both batteries, sized per the manual.
- Connect the trigger signal you’ve chosen.
- Connect the PC application over the USB A-to-B cable and set the input and output voltage, charge-current limit, input-current limit and battery charge curve.
- Start the engine and confirm the input and output LEDs show engine detection and charging.
Temperature Limit
The converter reduces output as it reaches its temperature limit, protecting itself and its wiring in hot conditions, then returns to full output as it cools. Mount it out of the engine bay where possible, in a space that stays below its 60°C upper rating.
Is It Right for Your Build?
Think about current, setup style and monitoring.
The Buck-Boost suits installers who want high current and fine control of input current, and who are comfortable setting it once from a laptop. If you want Bluetooth monitoring, the Orion XS or Orion-Tr Smart are simpler choices at lower currents.
FAQ
Does the Victron Buck-Boost DC-DC work with Euro 6 smart alternators?
Yes. Victron designed it for smart alternators, regenerative braking and Euro 5/6 engines.
Can I set it from my phone?
Not according to the datasheet, which lists a PC application over USB.
Can it charge a 24V house battery from a 12V vehicle?
Yes. Any 12/24V combination is supported, set in software.
Does it switch off when parked?
Yes. Engine-running detection or the ignition signal turns it off, and power-save mode draws 7mA.
Can several Buck-Boosts run in parallel?
Check the manual for paralleling guidance. For more current, the 100A model is the simpler single-unit choice.
Does it work with lead-acid batteries?
Yes. The charge curve is set in the PC application, so it can be configured for lead-acid, AGM, gel or lithium.
Sources: Victron Buck-Boost DC-DC Converter 25A/50A/100A datasheet; Orion XS and Orion-Tr Smart datasheets, victronenergy.com, accessed Oct 2026.
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