Marine system design

[MikeNorge78]

Need some help with design. My boat is 40ft and I liveaboard full time. I’d like help with coming up with a design. All systems are 12v dc or 120ac. Thinking about a 24v or 48v system with a step down transformer to 12v is this a good idea??

 

[wholybee]

The first thing you need to do is list every device you need to power, how much power it uses, and how many hours per day it will be turned on. Everything else is determined from the needs of that list. On a 40 foot boat with a diesel engine, there is usually little reason to use 24v or 48v. If you have several large appliances, an all electric galley, etc. then there is an argument for it, but most boats still use propane for cooking.
There are DC-DC converters to convert from higher DC voltage to 12V. They are not cheap, and are current limited. They work fine if you only have a few 12V devices and most everything is at the higher voltage.

 

[Crowz]

Step down works great if the load isn't to much. The larger the step down needed the more it cost for the step down unit from my experience.

On the flip side making ac from dc the higher the volts going into the inverter the better so 48 volts is ideal.

Now to find the middle ground.

On a boat you are not likely to need a bunch of watts normally. If you can stay at 1500 watts or less then 12 volts is great.

If you go from 2000 watts to 3000 watts 24 volts is better.

3000 watts all the time or higher 48 volts is where I would aim for.

Also the more watts needed means more solar watts needed to recharge the batteries. With a boat your limited on places to put the panels so were back to keeping wattage as low as possible.

Last piece of the puzzle is needed from you. What are you needing to run AC wise? What is the total watts need to be powered at one time?

 

[wholybee]

I would stay with 12V even up to 3000W, unless I had almost no 12V equipment, and heavily relied on 120V appliances. But it is a judgement call. The 12V equipment is often critical for safety. Radios, navigation lights, autopilots. I would want that connected directly to a 12V source if possible.

The other consideration with higher voltages is charging. Price a 48V alternator. Solar panels don't usually work well in series on a boat, but you will need to get voltage up to 60V+, so several panels in series.

 

[Horsefly]

I've only helped upgrade one sailboat. It was a 42 ft "Island Packet" that may (or may not) be similar to the OP's boat.

My observations: Loads on a boat are mostly either pretty small 12V DC (lights, and such) or really big 12V DC (winches, windlass, and especially a bow thruster). There are a few medium-sized 12V DC loads (bilge pump, and maybe a fridge), and a very few 120VAC loads (microwave). In our case it was obvious that 12V LFP was great for the house battery for the small/medium DC loads and the inverter, but a good old AGM bank was needed for the big DC loads. We also had an AGM battery for the motor starter, and then we had DC-to-DC chargers between the three banks.

The bow thruster by itself was 480A at 12VDC. You're not going to do that - at least not easily - with LFP due to BMS constraints.

I'm a fan of doing bigger than 12V for many things, but I'm not sure it is a good idea for a 40' boat.

 

[TimE]

I think the thing that gets lost on these threads is that once you go to Lithium your options on how you run your boat can change dramatically.
If you want to keep a fairly basic set up that just replaces what your lead did then you can do that. The benefit of lithium, to some extent is then wasted. When we made the jump to lithium, we also started to do 99% of our cooking on an induction hob because our solar performance almost doubled. The solar need never go off bulk. Forget the charging to 100% for good battery life every day. With lithium, you don't want to do that.
The first thing I would recommend is cramming as much solar on to the boat as you are happy with. In sunny climes, this will run your boat most of the time.most of the time, we run the watermaker, cook and make hot water, all of solar. We don't need the engine routinely to charge. If you do, then the system design would be different.
If you can give a bit more information on how you intend to use the boat, it would be easier to advice on what might be appropriate for you

 

[wholybee]

I think the thing that gets lost on these threads is that once you go to Lithium your options on how you run your boat can change dramatically.
If you want to keep a fairly basic set up that just replaces what your lead did then you can do that. The benefit of lithium, to some extent is then wasted. When we made the jump to lithium, we also started to do 99% of our cooking on an induction hob because our solar performance almost doubled. The solar need never go off bulk. Forget the charging to 100% for good battery life every day. With lithium, you don't want to do that.
The first thing I would recommend is cramming as much solar on to the boat as you are happy with. In sunny climes, this will run your boat most of the time.most of the time, we run the watermaker, cook and make hot water, all of solar. We don't need the engine routinely to charge. If you do, then the system design would be different.
If you can give a bit more information on how you intend to use the boat, it would be easier to advice on what might be appropriate for you

All true. The OP hasn't come back yet. Until he does and provides a list of all his anticipated loads (both AC and DC) I don't think we can give any more advice.

 

[RockOn]

Folks - I reviewed this thread and also am planning a system for a 40' aft cabin live aboard.
Please take a look.
My pref is one isolated system to feed the whole boat with only 2 connection interface (inverter to vessel ground and 110v to a 2 position switch)
- keeps 4 banks charged
- keeps components down
- keeps system separated from current house set-up for easier install
- downside loose some efficiency from charging DC to 110 to DC
2nd page is more tritonal set-up with a system for each bank.
- more components
- more wiring to run
- less clean set-up (inverter system stays the same so 3 installs vs 1 basically)

Comments please?

 

[TimE]

Folks - I reviewed this thread and also am planning a system for a 40' aft cabin live aboard.
Please take a look.
My pref is one isolated system to feed the whole boat with only 2 connection interface (inverter to vessel ground and 110v to a 2 position switch)
- keeps 4 banks charged
- keeps components down
- keeps system separated from current house set-up for easier install
- downside loose some efficiency from charging DC to 110 to DC
2nd page is more tritonal set-up with a system for each bank.
- more components
- more wiring to run
- less clean set-up (inverter system stays the same so 3 installs vs 1 basically)

Comments please?

Why do you need 370w of solar to charge an engine battery? I keep a pair of 100Ah series wired engine batteries charged with a 40w panel.
You would be way better off with all the solar going to the domestic battery bank and charging engine batteries from the domestic battery with a B2B charger.
Why is the domestic battery bank so small? We have 560Ah of lithium and will be doubling that soon

 

[RockOn]

Per the diagram - solar not to charge the backup start batteries - these are emergency backup only and are not deep cycle but high CCA.
Those are only on the ProMariner charger when on shore power prior to a trip so are 100%.
If you look at 2nd page, they are not connected to solar. Page 1, they are but only as the ProMariner is in operation through the inverter, but since they are 100% leaving the dock, I wouldn't suspect them to be drawing a charge.

My house bank 1 and bank 2 are the OEM joint start/house bank setup - not isolated start and house... so these will be solar charged when when on the hook along with the inverter bank.

Hence my questions about (1) 1100 watt system charging inverter bank and then powering everything through the inverter.
Or (3) 370 watt systems charging the 3 banks (house 1, house 2, and inverter).

As far as battery capacity - would rather put the $ in the solar setup since I already have the panels.
My calcs show I should be able to remain on the hook indefinitely and not have to ration power consumption.
For either option, I can always swap from AGM to LiPo batteries a bank at a time to double capacity as the MPPTs and my ProMarier can handle.

 

[RockOn]

No more thoughts