24V or 12V System

A

azk101

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Hello

I'm speccing out a potential new 42’ boat that still has mostly 2000s-era equipment and systems. They work fine for now, but I want to start the first phase of a power upgrade: roughly 800–1000 W of solar and some lithium batteries, with enough room to expand the bank later once we upgrade the rest of the systems. The goal is to move towards being as off-grid as practical.

My question is: should I begin with a 12 V system or go straight to 24 V, using 3 or 4 DC-DC converters to group loads where needed? My feeling is that 24 V is the better long-term choice. If I spec the inverter, MPPTs, and cabling correctly for the end-game system, then I should be able to add another round of batteries and solar later without redoing the backbone, right?

Rough estimates for our initial max daily consumption (I think):
12V
Sailing – 2180 Wh / 180 Ah
At anchor – 1650 Wh / 138 Ah

24V
Sailing – 2180 Wh / 90 Ah
At anchor – 1650 Wh / 70 Ah

Cheers
A
 
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wonkywinch said:
I personally think so much kit is available for 12v that it makes life much easier.
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That's my thought as well.

12v allows you to use caravan/camper kit, which should be a lot cheaper than specialist 24v stuff. For anything that's really power hungry - cooker, etc, you'll generally be better off using AC and a nice chunky inverter anyway.
 
Stemar said:
That's my thought as well.

12v allows you to use caravan/camper kit, which should be a lot cheaper than specialist 24v stuff. For anything that's really power hungry - cooker, etc, you'll generally be better off using AC and a nice chunky inverter anyway.
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I agree

So make sure your inverter is big enough to meet your future off grid ambitions, induction hob, air fryer, microwave, bread maker, toaster, kettle, coffee machine, etc - and consider you might want to use many of these items all at once.

Jonathan
 
There is plenty of 24V equipment out there, our boat is 24V and the only things we have that are 12V only are the VHF and the N2K network, which run via a Victron DC-DC converter. We do have 12V lights, but that was my decision, so i can run them through a DC-DC converter for a stable voltage.

We have a 3000W inverter, which would draw 150A at full power, whereas a 3000W 12V inverter would draw 300A. Cabling and fuses for 24V are half the size of those needed for the same 12V systems. 24V is more efficient and suffers less voltage drop than 12V.
 
Neeves said:
I agree

So make sure your inverter is big enough to meet your future off grid ambitions, induction hob, air fryer, microwave, bread maker, toaster, kettle, coffee machine, etc - and consider you might want to use many of these items all at once.

Jonathan
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I'm not sure you'd be able to use a kettle with anything else. They usually draw 3kw, designed so as many (inc UK) plugs are limited to 13A (3kw) and domestic ring mains are fused at 32A but this allows for diversication using a wired ring main (ie two 2.5 sg mm cables to each outlet).

I doubt you'd go for such sophistication on a boat and in any case, the biggest practical inverters are rated at 3kw.

Careful power consumption budgeting would still be needed. Start running all those loads and you'll need some beefy method of putting the energy back into the batteries.
 
azk101 said:
My question is: should I begin with a 12 V system or go straight to 24 V, using 3 or 4 DC-DC converters to group loads where needed? My feeling is that 24 V is the better long-term choice. If I spec the inverter, MPPTs, and cabling correctly for the end-game system, then I should be able to add another round of batteries and solar later without redoing the backbone, right?
Click to expand...
24V wiring can be half the size of 12V cable, so if you don't start with 24V now you'd have to use cable suited for 12V, ie, twice as big as you'd need for 24V.
 
PaulRainbow said:
There is plenty of 24V equipment out there, our boat is 24V and the only things we have that are 12V only are the VHF and the N2K network, which run via a Victron DC-DC converter. We do have 12V lights, but that was my decision, so i can run them through a DC-DC converter for a stable voltage.

We have a 3000W inverter, which would draw 150A at full power, whereas a 3000W 12V inverter would draw 300A. Cabling and fuses for 24V are half the size of those needed for the same 12V systems. 24V is more efficient and suffers less voltage drop than 12V.
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This, exactly.

I had 12v boats for decades, then 16 years ago bought my current one, which is 24v, and it's chalk and cheese. Reminiscent of going from a 6v car (dating myself here) to 12v. I would never go back to 12v for handling bulk power.

Besides much better cabling and fuses, it's all just much safer as the currents are half. And more efficient.

Large consumers like windlasses, winches, bow thrusters all run far better on 24v than 12v.

The only gear which you can't easily find in 24v are your NMEA2000 network and certain electronics; you just run those off cheap Victron droppers. Bringing the additional very significant benefit that you now have a stabilised power supply for your electronics which is isolated from voltage fluctuations and surges.

I wouldn't even consider 12v fitting out a new to me boat. No way. The question for me would rather be 24v vs. 48v. 48v is even much better for a lithium power system, high output alternator, etc.
 
Neeves said:
I agree

So make sure your inverter is big enough to meet your future off grid ambitions, induction hob, air fryer, microwave, bread maker, toaster, kettle, coffee machine, etc - and consider you might want to use many of these items all at once.

Jonathan
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You're going to power that "chunky inverter" with 12v?
 
wonkywinch said:
I'm not sure you'd be able to use a kettle with anything else. They usually draw 3kw, designed so as many (inc UK) plugs are limited to 13A (3kw) and domestic ring mains are fused at 32A but this allows for diversication using a wired ring main (ie two 2.5 sg mm cables to each outlet).
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I agree, if you are boiling a standard, quick boil, kettle on a 16A shore power supply and you turn just about any of the appliances Jonathan lists, the MCB will trip. The statement "you might want to use many of these items all at once." would be wishful thinking in most instances.
wonkywinch said:
I doubt you'd go for such sophistication on a boat and in any case, the biggest practical inverters are rated at 3kw.
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Depends on the boat. Our boat is on a ring main, although a lot of small boats are on radial circuits. There are much bigger inverters than 3Kw, suitable for boats and the better ones can be run in parallel.
wonkywinch said:
Careful power consumption budgeting would still be needed. Start running all those loads and you'll need some beefy method of putting the energy back into the batteries.
Click to expand...
That's true. If you're all electric you need to consider how much stuff you can use at a time, taking into account the amount of power you can draw (inverter size, shore power supply, generator size....

When we first bought this boat (all electric) it did not have an inverter or solar, just a 16A shore power supply and a large, 12Kva generator. With a 3Kw kettle and a 3Kw immersion heater we tripped the MCB many times. You never knew when the immersion was on and if it did happen to be on when you turned the kettle, hob, microwave on, it tripped every time. So i fitted a timer and set it so the immersion comes on for an hour, early in the morning before we get up. I then swapped the kettle for a 1100W one, take a bit longer to boil, but we can use other equipment now without tripping the MCB.
 
Another vote for 24v. Our boat was built in 1980 as a 24v boat. The engine is also 24v starting. If you are considering lithium, there are lots of advantages of 24v.
Mppts are rated in amps so you can use smaller ones or less of them. Battery cables are so much smaller at 24v. Lithium bms are rated in amps. You can handle twice the power for the same size bms. DC motors always run cooler at higher voltage.
In my opinion, all new production boats over 40ft should be 24v but builders don't care
 
geem said:
Another vote for 24v. Our boat was built in 1980 as a 24v boat. The engine is also 24v starting. If you are considering lithium, there are lots of advantages of 24v.
Mppts are rated in amps so you can use smaller ones or less of them. Battery cables are so much smaller at 24v. Lithium bms are rated in amps. You can handle twice the power for the same size bms. DC motors always run cooler at higher voltage.
In my opinion, all new production boats over 40ft should be 24v but builders don't care
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I don't know if the OP is considering lithium power, but lithium is a further strong argument for 24v (if not 48v). 12v lithium batteries are only 4 cells so you need to massively parallel them for a reasonable amount of 12v power. You need twice the number of BMS's and twice the number of fuses and it quickly becomes a mess.

What concerns inverters -- a 3000VA inverter is only good for 2500W or so and is at the limit of practical DC cabling size for 12v. 5000VA is a much better size for a boat with electric cooking etc., and AFAIK those are not even available in 12v.
 
24V is the better choice.

There is no need for 3 or 4 converters; almost everything will run off 24V. The only exceptions, as others have noted, are the NMEA 2000 backbone and, usually, the VHF.
 
Dockhead said:
….

Large consumers like windlasses, winches, bow thrusters all run far better on 24v than 12v.

……
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I would agree with that - 24V better for the big expensive kit like electric windlasses, winches, bow thrusters etc, particularly on bigger boats 40 feet or so upwards.
BUT the OP has not said what boat size he has.
And buying new 24V bow thrusters, electric winches, windlass etc starts to add £20k or so to the project !

For the other stuff (navigation, lights, domestic water pump etc) 12V is fine. And if going cooking etc then 240V better. So is there enough NEW 24V equipment going in to justify a 24V system?
 
dunedin said:
I would agree with that - 24V better for the big expensive kit like electric windlasses, winches, bow thrusters etc, particularly on bigger boats 40 feet or so upwards.
BUT the OP has not said what boat size he has.
And buying new 24V bow thrusters, electric winches, windlass etc starts to add £20k or so to the project !

For the other stuff (navigation, lights, domestic water pump etc) 12V is fine. And if going cooking etc then 240V better. So is there enough NEW 24V equipment going in to justify a 24V system?
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The main reason for 24v vs 12v is your inverter wiring, battery charger wiring, and alternator, if you don't have any high powered DC gear. And the battery itself if you're lithium. That's plenty of good reason to go 24v, and with lithium and/or high powered inverter it may be even essential.

I agree that low-powered DC gear such as the things you mentioned run OK on 12v, but pumps, lighting, nav lights, etc. are all available in 24v without cost penalty.

So even in the absence of high powered DC gear, I would still go with 24v.
 
dunedin said:
I would agree with that - 24V better for the big expensive kit like electric windlasses, winches, bow thrusters etc, particularly on bigger boats 40 feet or so upwards.
BUT the OP has not said what boat size he has.
And buying new 24V bow thrusters, electric winches, windlass etc starts to add £20k or so to the project !

For the other stuff (navigation, lights, domestic water pump etc) 12V is fine. And if going cooking etc then 240V better. So is there enough NEW 24V equipment going in to justify a 24V system?
Click to expand...
You can have nav lights, domestic water pumps, lighting, autopilot, ais, bilge pumps, all at 24v if you are starting from scratch as well.
I have found 24v stuff seems so much more reliable than 12v stuff as well. I don't know why that should be
 
Great wealth of knowledge and opinions here, thanks all.

I think I’m leaning towards the pro 24V camp. We do plan to increase our power usage over time and aim to be as self-sufficient and off-grid as possible, so building the system in 24V feels like the sensible long-term move. And with more kit shifting towards 24V these days (so i believe), it probably helps future-proof the boat a bit and might even make it more appealing when it comes to resale.

Copy on the inverter, I was planning for a 3k version already so all good there.
|

Quick follow-up 🙋🏻

Victron or Fogstar LiFePO - or is there another brand people here rate? I’ve seen Battle Born mentioned a lot but they don’t seeeem easy to get in the UK.

Also, any recommendations for decent solar panel brands or a good all-in-one supplier to talk to for all power needs?
 
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azk101 said:
Great wealth of knowledge and opinions here, thanks all.

I think I’m leaning towards the pro 24V camp. We do plan to increase our power usage over time and aim to be as self-sufficient and off-grid as possible, so building the system in 24V feels like the sensible long-term move. And with more kit shifting towards 24V these days (so i believe), it probably helps future-proof the boat a bit and might even make it more appealing when it comes to resale.

Copy on the inverter, I was planning for a 3k version already so all good there.
|

Quick follow-up 🙋🏻

Victron or Fogstar LiFePO - or is there another brand people here rate? I’ve seen Battle Born mentioned a lot but they don’t seeeem easy to get in the UK.

Also, any recommendations for decent solar panel brands or a good all-in-one supplier to talk to for all power needs?
Click to expand...
Battleborn are over priced for a very average battery. Ditto Victron. Fogstar would be my recommendation.
 
azk101 said:
Great wealth of knowledge and opinions here, thanks all.

I think I’m leaning towards the pro 24V camp. We do plan to increase our power usage over time and aim to be as self-sufficient and off-grid as possible, so building the system in 24V feels like the sensible long-term move. And with more kit shifting towards 24V these days (so i believe), it probably helps future-proof the boat a bit and might even make it more appealing when it comes to resale.

Copy on the inverter, I was planning for a 3k version already so all good there.
|

Quick follow-up 🙋🏻

Victron or Fogstar LiFePO - or is there another brand people here rate? I’ve seen Battle Born mentioned a lot but they don’t seeeem easy to get in the UK.

Also, any recommendations for decent solar panel brands or a good all-in-one supplier to talk to for all power needs?
Click to expand...
Where in the UK are you ?
 
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