12v, 24v or 48v on sailboat

Howdy all, I am looking for some advice.

The backstory: I am the proud owner of a new Lagoon 42 catamaran that I bought as a boat show model. It came with a bunch of options that look great at boatshows and may or may not have been my choice if I was buying new (my wife and I never imagined we would buy a new boat but a deal is a deal). We are outfitting the boat for the bigger picture which includes longer term liveaboard cruising. The electric systems are by far the biggest expense and cognitive investment. My current setup is 560ah of AGMs, no solar, no inverter, a 13.5kw generator, 2 big 12v electric winches (180 amps at max working load each) and of course, a 12v windlass (100 amp breaker). In general the dc appliances and electronics will stay (all 12v) as will the electric winches and windlass. The Yanmar engines have stock alternators.

I have calculated I will need about 900-ish amp hours per day depending on whether I am at anchor or underway which includes estimated inverter loads (no A/C, washing machine, ice maker, etc). I considered beefing up on additional AGM but I will need close to 1,000 lbs of batteries if I use AGM (1400ah) so I am considering switching to LifePO4 and I am considering building them from 280ah cells.

I think I understand the primary pros and cons of the various voltage configs for these batteries. While a keep it simple approach is likely out the window, simplicity and managability are high on the requirement list. So my current thinking is:

• If I am going to anything other than 12v, 24v really doesn't make any sense over 48v
• From the battery to the inverter / AC circuit stuff, should be pretty straight forward
• The small load DC stuff should also be pretty easy to step down for as the amperage will not necessitate big hardware
• The complication comes with the existing engine and generator batteries and the 12v big draw items (winches and windlass)

My questions are:

1. Does it make sense to go 48v?
2. If so, what would make the most sense on the winches and windlass (or what are the options)?
3. At this high level of thinking, am I missing anything important?

Thanks,

Chris

Those winches!! They are definitely holding you back. I am always in favor of using more volts as opposed to less however in your situation it is going to be very hard to find a step down converter to move that many amps. You said you need 900Amp hours per day I think you meant 900 watt hours is that correct?

Hmmmm this is an interesting conundrum. The high current 12V items are pretty beefy. Are there 24V or 48V to 12V converters that will handle that kinda load? I guess there must be and this problem must have been solved somewhere already. I’m interested to find out what it is.

With loads that high a 48V system has got to have better efficiencies over all and would give plenty of room for a beefy inverter in the future.

Just guessing I’d be looking at putting individual 48V to 12V converters as close as possible to the big load items to reduce voltage losses on cable runs.

Then a more normal 12V circuit to run dc lights and fridges etc. 48V to inverter for an AC circuit.

I did wonder if splitting the batteries to create 2 seperate specification circuits, one for 12V high load items and one for normal house loads but I think 48V and seperate 48V to 12V converters at the load source would make more sense from the cabling perspective.

But I’m just guessing. Like I say it will be interesting to see what’s recommended.

Craig said:

Those winches!! They are definitely holding you back. I am always in favor of using more volts as opposed to less however in your situation it is going to be very hard to find a step down converter to move that many amps. You said you need 900Amp hours per day I think you meant 900 watt hours is that correct?

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I calculated that in amp hours and have since reduced some of my assumptions. I have probably still calculated poorly. Here is the worksheet for my loads. I'm sure some real world experience will help me get it to a more realistic number.

ianganderton said:

Hmmmm this is an interesting conundrum. The high current 12V items are pretty beefy. Are there 24V or 48V to 12V converters that will handle that kinda load? I guess there must be and this problem must have been solved somewhere already. I’m interested to find out what it is.

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This is about 35% of the problem with the rest being the overall complexity of mapping 12v to the needed locations and managing the house vs start batteries.

Nice Boats . Lower voltage is probably a little safer in a wet environment. So the 12 volt system is in and working ? You just want to add inverter with solar/wind charging ? and what is your intended usage of the boat ?

tazmann said:

Nice Boats . Lower voltage is probably a little safer in a wet environment. So the 12 volt system is in and working ? You just want to add inverter with solar/wind charging ? and what is your intended usage of the boat ?

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Yes, 12v is working. I am going to add an inverter and solar (not wind gen). I have a 13.5kw diesel generator that is already a sunk cost. I want to add energy and storage capacity to live off the batteries for at least 2 days. We will be cruising in the future - some will be pretty remote. I am not planning to run air conditioner off the batteries yet (I have the big generator for that).

You are pretty much committed to 12v with all the existing items. If you manage the simultaneous AC device useage then 12v inverter is doable.

I would be a careful about 280 AH LFP cells with exposed thin aluminum cases in marine environment.

Many mariners want to keep their engine starter batteries separately isolated, and even duplicated, so there is minimual chance of over draining from equipment on board and end up unable to start engine.

I have a Lagoon 380S with a 12volt system. If I was starting from scratch I would probably go with 24v but like you, my boat was already equipped with all the 12v parts.

Keep it simple and stay with 12v. I had 800Ah of AGM but I just changed them out for 600Ah LiFePo4. 520w of solar panels over the davits and a Xantrex charge/inverter for 120vac. I have my 12v Isotherm refrigerator on all the time and I crossed the Pacific Ocean with all my Raymarine equipment on day and night (including autopilot).

You will be just fine with the 12v system and a solar setup to keep your batteries going. With that big genset you won't have problems on an overcast day.

My biggest power draw is my 12vdc Dessalator water maker. You need a watermaker if you plan on making long passages.

Mango boat said:

My biggest power draw is my 12vdc Dessalator water maker. You need a watermaker if you plan on making long passages.

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I have that on my power plan though I don't own it yet.

Where is your cruising location? Are you planning on longer passages, maybe crossing an ocean or two?

Since the 12 volt system is in and the charging system more that likely can't do LFP batteries my suggestion would be a separate 24 volt system for the inverter. A 24 volt inverter charger with LFP battery bank, Looking at youre AC loads at bare minimum you could get by with 2000 watt inverter 3 to 4000 watt would be better but that is up to you. Your solar system would need to split two charge controllers one for 12 volt and one for 24 volt,
Simplest system would be keep it all 12 volt with as much solar as can and stick with agm

Mango boat said:

Where is your cruising location? Are you planning on longer passages, maybe crossing an ocean or two?

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Yes, the plan is to do extensive longer term cruising including crossing oceans.

tazmann said:

Since the 12 volt system is in and the charging system more that likely can't do LFP batteries my suggestion would be a separate 24 volt system for the inverter. A 24 volt inverter charger with LFP battery bank, Looking at youre AC loads at bare minimum you could get by with 2000 watt inverter 3 to 4000 watt would be better but that is up to you. Your solar system would need to split two charge controllers one for 12 volt and one for 24 volt,
Simplest system would be keep it all 12 volt with as much solar as can and stick with agm

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I respectfully disagree and here's why...

The OP already has a 13.5kv generator installed providing plenty of 120vac as needed.

Typically, you won't need more than 12vdc for EXISTING lights, pumps, winches, windlass, running lights, autopilot, navigation equipment, toilets, bilge pumps, etc.. This would be an expensive venture to convert to 24vdc and astronomically expensive for 48vdc. A single Harken 12v winch runs around >$6k and a bit more for 24v.

The OP intends to install solar panels so it makes sense to go with LiFePo4 setup in 12v. AGMs are bulky, heavy and don't last as long. In a catamaran you are always looking for ways to keep it light.

A 24v stand alone LiFePo4 system would just add weight and have no useful purpose. Nothing on his boat uses 24 or 48 volts now so why add something that you would have to convert?

Two engines with 2 alternators both charging 12vdc. Let those charge the lead-acid engine start batteries with a DC-DC charger for the overflow to charge the LiFePo4 if needed.

You lose efficiency converting 24 or 48 to 12vdc. ALL the equipment I mentioned above would need to be converted or repla$$$ed. Best bang for the buck and the most utility would come from a 12v solar/LiFePo4 system.

crholliday said:

• If I am going to anything other than 12v, 24v really doesn't make any sense over 48v
• From the battery to the inverter / AC circuit stuff, should be pretty straight forward
• The small load DC stuff should also be pretty easy to step down for as the amperage will not necessitate big hardware
• The complication comes with the existing engine and generator batteries and the 12v big draw items (winches and windlass)

My questions are:

1. Does it make sense to go 48v?
2. If so, what would make the most sense on the winches and windlass (or what are the options)?
3. At this high level of thinking, am I missing anything important?

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Sticking with just the questions in relation to your current configuration these would be my recommendations...

1. No, 48vdc does not make sense over your existing 12vdc config. Do you have a warranty with that nice Catamaran? What does Lagoon say about adding an incompatable system to your boat?

2. Electric winches are very pricey. You can just change the DC motor. Same with the windlass.

3. I think you are just growing into your boat and you need to talk with other sailboat owners near you. Go look at other people's boats and talk with them. A lot of good tours and recommendations will come out of your local sailing community. You will get some pretty interesting information that way.

Some of the best people I've ever met lived on a sailboat.

I have faced the exact same problem and no mater how hard I tried, I could not find a reasonable way to do anything other than 12 volts (I *really* prefer using higher voltages).

I came close to moving the Winch to the starter battery and then doing the house battery at 24V.... but with soooo much of the boat already running 12V I ended up just staying with 12V.

One of the biggest problems I have with 12V systems if finding a good high current BMS. I have not found one rated for over 120A that has the features I want (Such as low temp protection).

Note: I have not looked at 12V BMSs for several months. If anyone has a recommendation for a good high-current 12V BMS, please speak up.

Just a question what kind of priority is given to the various devices or systems? Thinking about your health and safety I would think that any sort of fire protection, a radio and the generator must be near the top of the list. Just curious.

evad said:

Just a question what kind of priority is given to the various devices or systems? Thinking about your health and safety I would think that any sort of fire protection, a radio and the generator must be near the top of the list. Just curious.

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I'm not sure if this question is being asked of me, but I also don't fully understand the context? I am looking at improving my ability to live on the hook and have no intention of compromising safety. This thread is exploratory to get feedback on ideas that aren't super easy to research.

Just curious I was reading the thread and wondered about the priority. Did not mean to imply that you or anyone else was ignoring safety.