Rewiring a sailboat in 24 V lithium

Going from a makeshift installation built up over forty years to a system designed for a circumnavigation. Here is the architecture we settled on, what each box does, the traps we hit and what the job cost.

Start by taking it all out

The first decision was the most drastic: disconnect the batteries and pull everything out. Not out of a taste for destruction, but because there was no other way of getting at the cables. What had been fitted before went too.

On an old boat, the electrics are sediment: every owner added his layer without removing the previous one. Until you strip the space back, all you are doing is adding one more stratum. In our ceiling voids, six cables out of eight were already cut and served no purpose.

That stage also freed up a proper dedicated space for the batteries, with a bulkhead right beside it to mount all the units on. A detail on paper; at sea, it is the difference between a fault you can fix and a fault you just have to live with.

Draw the diagram before you touch a cable

The system splits into two circuits that talk to each other.

The house circuit

1. The house batteries, wired in series to give 24 V.
2. A fuse, then a Lynx Power In.
3. The Lynx Distributor, which feeds everything out again: the inverter for 230 V, the main switch panel, and the charging inputs.
4. The charging inputs: the lithium charger and two Orion TR Smart DC-DC converters.
5. A SmartShunt on the negative, which actually measures what goes in and what comes out.

The engine circuit

The engine batteries have their own SmartShunt, are connected straight to the 24 V alternator, and join the boat’s common negative bus. A common positive busbar keeps the number of connections and cables down — fewer contact points, fewer points of failure.

The brain

It all reports to the Cerbo GX, the small onboard computer that gathers the system’s data in real time.

Why 24 V rather than 12 V

At the same power, doubling the voltage halves the current. In practice: smaller cable sizes, fewer losses along the run, less heating. On a 16-metre boat where the cable runs are long, the difference is not theoretical — you read it on the copper bill.

The trap that buys you a screen for nothing

The GX Touch display that plugs into the Cerbo shows state of charge, instantaneous consumption and every device on the system. Connecting it asks nothing of you: an HDMI, a USB, and it configures itself. Reckon on €230 to €290 depending on the dealer.

But for several battery banks to both show up on the screen, they have to be linked by VE.Direct. Over Bluetooth, they do not appear. It is the kind of detail you find out after buying the screen, and it decides which cable you run.

Once it is in, you read both banks at a glance: house and engine, each with its own percentage. At sea, that is exactly what you want to check in three seconds.

What the job cost

That is about €2,950 committed so far, not counting the GX Touch display or the solar panels and forward battery, both still to come. The running detail is on the budget page.

What we take from it

• Diagram first, tools second. Two and a half days of wiring are prepared in one evening with a pencil.
• A common negative bus and a common positive bus simplify everything and cut the number of connections.
• VE.Direct, not Bluetooth, as soon as you want several devices on one screen.
• Decide where the batteries go before you buy them. Moving a washing machine to free up a locker is quicker than rewiring a whole boat around a bad location.

Going further

The full video episode: one week to rewire the whole boat. The follow-up, with the screen going in: the engine runs, the teak lives, the ceilings come down.

To size your own installation — capacity, solar, cable sizes — the electrical configurator is free during the launch phase.