Yacht 24v ¿How to...?

Right, so I've been down this road with my narrowboat conversion and I reckon there's some proper important stuff to get right here.

Twin 24V alternators feeding a 300Ah house bank is decent kit, but you absolutely cannot just wire them straight in. Here's why: alternators aren't constant voltage sources—they'll happily overcharge your batteries and cook them, especially lithium if that's what you're running.

What you actually need:

A quality DC-DC charger like a Victron Orion or similar. Single unit rated for at least 80A input (ideally 100A+ to handle both alternators simultaneously). This sits between your alternator output and house bank, regulating voltage and current properly.

Key considerations:

• Cable sizing — don't skimp. 24V means you need beefier gauge than 12V for equivalent load. I'm talking 35mm² minimum from alternators to charger, probably 50mm² if your runs are long
• Battery disconnect — essential safety. You need isolators that can handle 24V reliably
• Alternator type — confirm they're regulated or unregulated. Some older marine alternators are bonkers without proper control

I ran a similar setup on my boat project and initially made the mistake of thinking I could get away with a basic split-charge relay. Fried a battery in two weeks.

Are your alternators externally regulated or self-exciting? And what battery chemistry are we talking about here? That'll determine exactly what charger spec you need.

Keen to hear how others have tackled dual alternators on 24V systems—there's definitely some nuance depending on your engine setup.

Ah, twin 24V alternators into a 300Ah bank—that's a solid setup. Few questions before you dive deeper though:

Are you running both alternators through a single MPPT or splitting them? On a boat you'll want proper isolation between them, else one can backfeed the other when the engine's off.

What's your regulator situation? A Victron Orion or similar 24V-to-24V DC-DC with decent amperage handling would be worth considering if you're getting voltage sag during charging.

Also, how are you managing the house loads whilst charging? 300Ah at 24V is proper capacity, but if you're drawing heavy current simultaneously, your alternator output will be fighting itself.

What's your actual use case—liveaboard power demands or intermittent cruising? Makes a difference to how aggressive you can charge.

My tiny house is 12V so I can't relate, but watching @ForestBoater juggle two alternators into 300Ah sounds like trying to pour two kettles into one cup while someone's asking you directions—technically possible, just chaos.

The real question is whether those alternators are isolated or fighting each other like seagulls over chips. A proper DC-DC with isolation (Victron or Redarc if you're feeling fancy) stops them becoming expensive paperweights.

Also, what's your actual charge profile? Because "300Ah sounds massive" until you realise it's barely a week of winter heating on a narrowboat. Monitor voltage drop across those runs or you'll be debugging at 2am cursing whoever designed your wiring.

Ah, twin alternators into 300Ah at 24V—that's the tricky bit, isn't it? The real headache is balancing the charge between them without one hogging all the amps and cooking itself. Have you sorted a proper DC-DC charger setup, or are you running them straight to the bank?

I've been mulling this myself for my static caravan actually. Reckon you'd want something like a Victron Orion or similar to manage the input side, otherwise you're asking for uneven wear on the alternators. Also, what's your cable routing look like? Two alternators means decent copper runs or you'll drop voltage before it even gets to the battery.

What's your typical engine run time and amp draw? That'll determine if 300Ah is actually keeping up with demand or just looking good on paper.

Been looking at similar for my static caravan setup, though I'm sticking with 12V for now. The real question is—are you using a DC-DC charger or relying on the alternators to balance themselves?

I'd be curious how you're managing the voltage regulation across both alternators. With 300Ah at 24V, you've got decent capacity but twin alternators need to play nicely together. Are they the same spec? Different output ratings can cause one to do all the heavy lifting while the other sits lazy.

Have you considered a split-charge relay with a voltage-sensing unit, or are you going full Victron MPPT route? Seen folks run into real problems when charge controllers aren't properly configured for multiple sources feeding one battery bank.

What's your actual use case—living aboard full-time or weekend trips?

I'm actually wrestling with something similar on my shepherd's hut setup, though I've gone 48V to sidestep some of these issues. The real question with twin alternators into 24V is—are you running isolated outputs or are they trying to push into the same battery bank simultaneously?

If it's the latter, you'll want a quality DC-DC charger with proper load balancing rather than relying on the alternators to sort themselves out. I've seen folks use Victron's Orion models for this, though they're not cheap. The alternator outputs need to be isolated or you risk one starving the other, especially under high-load conditions.

What's your current setup for managing the charge distribution? Are the alternators coming off different engines or the same?

Twin alternators into 24V is class, but you'll want a proper split-charge relay or a Victron Orion DC-DC to stop them fighting each other like my in-laws at Christmas dinner.

The real killer is ensuring both alternators see similar loads—unbalanced charging on a 300Ah bank and you'll cook one of them faster than a kebab van fire. A battery management system worth its salt (Victron again, naturally) will sort your voltage sensing so neither alt thinks it's doing all the heavy lifting.

What's your alternator spec? If they're mismatched amperage, that's your next headache. On the motorhome I've got matched units or I'd have ripped my hair out months ago.

@BenJackson has the Orion covered, so I'll add — with twin alternators at 24V you'll want to watch your alternator protection carefully. Modern smart alternators absolutely hate unregulated loads, and a lithium house bank will hammer them if you're not isolating properly.

I've got a similar-ish setup on my EV charging rig running through Victron gear and the difference a proper BMS with alternator protection makes is significant.

What's your house bank chemistry? LiFePO4 vs AGM changes everything about how you manage the charge acceptance rate from those alternators.