Sailing Vessel Refit: Replacing the Sterling ProAlt C with Victron Orion-Tr Smart

DIY
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Vessel & System Overview

Dufour 405 GL (2011), 12V DC system,

  1. House bank: 3 × Victron Gel Deep Discharge 12V/110Ah (BAT412101104) — 330Ah total
  2. Start battery: 1 × 110Ah
  3. Alternator: Volvo Penta D2-40/55, confirmed 115A output

**Question:**I am considering replacing the Sterling ProAlt C with a Victron Orion-Tr Smart. My installation company has recommended two Orion-Tr Smart 12/12-50 units — one for the house bank and one for the starter battery.

My concern is that the combined draw would exceed the alternator’s rated output:

  • 2 × 50A output = 100A B2B charging draw

  • Typical underway DC loads (instruments, autopilot, fridge, lighting) = ~28A

  • Total estimated draw = ~128A against a 115A alternator

Specific questions:

  1. Does the combined draw of two 12/12-50 units plus normal DC loads exceed a safe operating threshold for a 115A alternator, even with input current limiting engaged?

  2. Is a 50A B2B charger justified for a 110Ah starter battery, which is only used for engine starting and sees minimal discharge?

  3. Would a single Orion-Tr Smart 12/12-30 to the house bank, combined with either a VSR or the MultiPlus 1A trickle output for the starter battery, be a more appropriate specification for this installation?

Any experience or guidance from the community — particularly from those with similar alternator ratings and bank sizes — would be very welcome.

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The Sterling Pro Alt C is an alternator to battery chargers and does not need a battery on the alternator output.

The Victron Orion units are battery to battery units and the alternator output must have a battery. Look in all the install manuals, they show the alternator charging the starter battery and the Orion charging the house battery.

When people have connected an Orion direct to an alternator they have reported voltage swings as the alternator voltage regulator interacts with the voltage control on the Orion input. Both controllers are trying to control the same voltage by varying the same current. Not saying this will definitely happen but it is seen frequently. A battery decouples supply and demand current and buffers the voltage / current response. Alternator to battery chargers have different input voltage / current control to avoid this.

Secondly, you should only run an alternator at around 2/3 rated current continously at most, maybe a bit lower, depends on cooling, unless you have an alternator rated for max continuous current, which are rare.

For you, alternator charges the starter battery then you have a single Orion 50A to charge the house bank and supply the house loads. If you think this is not enough for domestic charging and loads then you could add 2 Orions between the starter and house but you would need to reduce the input current limit on the Orions. It all depends on what loads you have on the starter to know what is left for the house.

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Thank you very much for your time & expertise.