48V as main DC voltage on boat - anyone?

[Dockhead]

Originally Posted by StuM

Guess I'm not typical then. With alternators on both 40HP engines and 800W of solar panels, I've never felt the need for a generator

I always thought three diesel engines on a highly weight sensitive vessel like a cruising cat was daft.

If you're going to go to two diesel engines, then I think Stu's architecture makes the most sense by far. If you want to go to one, then hybrid with diesel in one hull is surely the way to do it, but then you've lost redundancy for both propulsion and power which you get from normal cat configuration with heavy duty alternators on both prime movers.

I think it's pretty hard to improve on this setup, and just to add even more to its appeal, it doesn't require any exotic technology or even non-standard parts.

[valhalla360]

Originally Posted by Dockhead

I always thought three diesel engines on a highly weight sensitive vessel like a cruising cat was daft.

If you're going to go to two diesel engines, then I think Stu's architecture makes the most sense by far. If you want to go to one, then hybrid with diesel in one hull is surely the way to do it, but then you've lost redundancy for both propulsion and power which you get from normal cat configuration with heavy duty alternators on both prime movers.

I think it's pretty hard to improve on this setup, and just to add even more to its appeal, it doesn't require any exotic technology or even non-standard parts.

If may be daft but for standard production boats it's pretty standard. Most people don't want to run that big 40hp motor when a 5-10hp generator can do the job more fuel efficiently...of course, if we start looking at boats logically, it doesn't make a lot of financial sense to own a large cruising boat in the first place.

Actually, you don't lose redundancy.
- The diesel is it's own self contained system.
- The electric side can be powered via solar, generator or if the propulsion diesel still runs but maybe the prop or transmission is damaged, the alternator can still supplement the electric motor. You likely will go slower but still can go.
- Plus so far, I think the assumption is a sail catamaran so in open water, you still have the sails.

The downside to Stu's option is you always must run on diesel. Not a huge issue but if you mostly do short local runs, you can likely cut fuel consumption significantly. A large battery bank that charges up over the week and provides sufficient power for 20 miles and/or running the air/con for a day or two may mean you rarely have to run the diesel generator or propulsion engines...but when the need arises, you have the capability.

In many ways this is more of a marketing solution. People want to feel like they are doing something good for the environment but when push comes to shove, they want the same capability. If you can give them that capability at the same cost, it should sell.

[Dsanduril]

The beauty of the serial hybrid model is that the one engine now has a 10-20kW motor/generator. Contrast that with a 1.5kW alternator (100A at 15V). If you like to live with all the modern conveniences you can now run the 40-50HP prime mover as your generator and actually put a decent load on it. If you have a high acceptance battery pack you can charge very quickly. And you have the option of running one or both props electrically. When motoring for long distances you can use a direct drive and still use the MG to generate 1-2kW for charging (essentially the same as having an alternator on the engine).

It does put all your eggs in one diesel basket, but lots of sailors have lived that way for a very long time (we do still have sails). On the flip side, a decent battery system and/or solar charging allow you to maneuver into/out of a marina without needing the diesel at all. I'm skeptical about being able to move to 100% electrical in the near future if you want to have a long range capability under power, but for 15-30 minutes of maneuvering I think it is quite feasible, thus if the diesel is dead you still have the ability to get into tight quarters if needed.

[RaymondR]

Engine and motor generator on the same shaft seemed to work well for U boats and other diesel/electric submarines.

[ranchero76]

Just to avoid confusion: parallel hybrid - when both electric motor and engine physically connected to final drive. Serial hybrid - when engine-generator is NOT connected to final drive.

[aybabtme]

Sorry for bringing up an old post, but I've been looking at the same thing. I'm thinking of bringing in:
- 48V battery bank
- 48V DC/AC inverter for AC supply
- 48V to 12V buck converter (it's like 60$ with high efficiency) for all existing wiring.
- 48V solar charger

And then every common thing stays 12V, but I have the option to run a 48V line to high load devices.

Why? Mostly because high current loads stress me out. Heat loss is the square of current (P = I^2 * R), so in my mind, having heavy loads on 12V system means running hot wires around the boat. It seems needlessly dangerous to me. Would prefer to run a 48V line to say, the windlass, and if the windlass is 12V then I bring the voltage down to 12V right there and minimize the long run of high amp wiring.

Also, having 48V allows for much higher efficiency converting to 120V AC, and much lower load on the battery bank (pulling much less amps for each cell). At last, I wouldn't see flickering/dimming lights anymore when a large DC load kicks off. There'd be less inductance on the system too, I bet.

I think that the "dangerous" 48V lines could be limited to runs between power devices, all the house wiring remains 12V, which also means no rewiring of existing systems would be required, and I could always pull the 48V parts out and put back old 12V batteries to sell if a potential buyer has some qualms.

Also extra kudos: stuff like CAT cables with PoE or USB-C with PD could be set in various spots for modern accessories and consumer electronics, which is super cool.

So it may sound like I'm fairly settled on the question. But I think it's always good to rubber-duck debug stuff against other people's hears.

For background, I'm a software engineer with a decent background in electronics (I designed circuits, PCBs and built little machines however limited experience in power electronics). I've been researching the topic quite a lot over the last few months.

[Dockhead]

A few comments, some of them from the devil's advocate's point of view, which I think is what you are looking for:

Originally Posted by aybabtme

Sorry for bringing up an old post, but I've been looking at the same thing. I'm thinking of bringing in:
- 48V battery bank
- 48V DC/AC inverter for AC supply
- 48V to 12V buck converter (it's like 60$ with high efficiency) for all existing wiring.

Be careful with the cheap stuff. RFI is a huge problem with really cheap buck converters. If your whole boat depends on this dropper, it really makes sense to use a top quality name brand one, like Victron.

Originally Posted by aybabtme

- 48V solar charger

And then every common thing stays 12V, but I have the option to run a 48V line to high load devices.

Why? Mostly because high current loads stress me out. Heat loss is the square of current (P = I^2 * R), so in my mind, having heavy loads on 12V system means running hot wires around the boat. It seems needlessly dangerous to me.

Well, again -- it's all in the numbers. If the cables are correctly sized, you will not get excessive heating, even at 6v. 12v certainly doesn't mean "running hot wires around the boat". That results from undersized cables, not the voltage of the system.

Originally Posted by aybabtme

Would prefer to run a 48V line to say, the windlass, and if the windlass is 12V then I bring the voltage down to 12V right there and minimize the long run of high amp wiring.

I think you need to balance the complexity and introduced point of failure of having a large capacity dropper next to the windlass (exposed to sea water?), against the cost and bulk of a cable adequate to give you the voltage drop and heating characteristics you want. Don't be emotional about it -- it's all a question of numbers. You can power a windlass with even 6v if the cable is fat enough.

Originally Posted by aybabtme

Also, having 48V allows for much higher efficiency converting to 120V AC,. . .

I don't think this is right. What is the difference, in numbers? I'm sure it's MORE efficienct, but MUCH MORE? I doubt it. Maybe 97% vs 96%? Is that enough to move the needle?

Originally Posted by aybabtme

. . .and much lower load on the battery bank (pulling much less amps for each cell).

I think this is fallacious -- the load is the same as a percentage capacity of the cell, IF the battery bank has the same A/H capacity. Because at 4x the voltage, the cells will have 1/4 the capacity. So there is no gain at all here.

Originally Posted by aybabtme

At last, I wouldn't see flickering/dimming lights anymore when a large DC load kicks off. There'd be less inductance on the system too, I bet.

I think that the "dangerous" 48V lines could be limited to runs between power devices, all the house wiring remains 12V, which also means no rewiring of existing systems would be required, and I could always pull the 48V parts out and put back old 12V batteries to sell if a potential buyer has some qualms.

Also extra kudos: stuff like CAT cables with PoE or USB-C with PD could be set in various spots for modern accessories and consumer electronics, which is super cool.

So it may sound like I'm fairly settled on the question. But I think it's always good to rubber-duck debug stuff against other people's hears.

For background, I'm a software engineer with a decent background in electronics (I designed circuits, PCBs and built little machines however limited experience in power electronics). I've been researching the topic quite a lot over the last few months.

I like the idea of higher voltage DC -- my present boat is 24v and I like the surprising sveltness of the cabling compared to the loads involved.


But she was originally built as 24v. When you start thinking about converting a boat to something different, it seems to me you need to take a good long hard look at the complexity and cost vs. practical results achieved. There's nothing magic about 48v vs 24v vs 12v -- it's all in the numbers.





Concerning hard-installation of USB-C and POE sockets around the boat -- a warning -- this stuff goes out of date and out of fashion, but a hard installation will be there for possibly decades. What happens when inductive charging devices become widespread? I have been tempted to do something like this, but keep stopping myself. And I'm glad I did -- for example, my phones and tablets now use Quick Charge 3.0. With a generic cigar lighter socket, I can just pop the new Quick Charge 3.0 device in. Had I installed hard wired USB sockets, I'd be SOL. My laptop has USB 3.0 charging. But what will the next one have? I'd hate to be chopping holes in cabinets to install something which will be obsolete by the time I change laptops next time (or the time after). Therefore I charge my laptop via the manufacturer's car charger (a beautifully designed very compact device), plugged into a bog standard cigar lighter socket.



I sail sometimes with a big crew, and so sometimes have up to a couple dozen small electronic devices on board needing daily charging. I gave up a long time ago trying to do something slick and efficient and purely DC. Now I just provide multi socket AC power strips and let people charge everything off the inverter or when I run the generator.



Simplicity is a supreme value in designing boat systems, which is worth fighting for, and which should be compromised only for a really compelling reason.


JMHO.

[aybabtme]

Just looping back quickly; by cheap 48-12DC buck converter, I meant the ~60USD Victron ones. Thanks for your response, I'll have a closer read in a few!

[ramblinrod]

Originally Posted by aybabtme

Sorry for bringing up an old post, but I've been looking at the same thing. I'm thinking of bringing in:
- 48V battery bank
- 48V DC/AC inverter for AC supply
- 48V to 12V buck converter (it's like 60$ with high efficiency) for all existing wiring.
- 48V solar charger

And then every common thing stays 12V, but I have the option to run a 48V line to high load devices.

Why? Mostly because high current loads stress me out. Heat loss is the square of current (P = I^2 * R), so in my mind, having heavy loads on 12V system means running hot wires around the boat. It seems needlessly dangerous to me. Would prefer to run a 48V line to say, the windlass, and if the windlass is 12V then I bring the voltage down to 12V right there and minimize the long run of high amp wiring.

Also, having 48V allows for much higher efficiency converting to 120V AC, and much lower load on the battery bank (pulling much less amps for each cell). At last, I wouldn't see flickering/dimming lights anymore when a large DC load kicks off. There'd be less inductance on the system too, I bet.

I think that the "dangerous" 48V lines could be limited to runs between power devices, all the house wiring remains 12V, which also means no rewiring of existing systems would be required, and I could always pull the 48V parts out and put back old 12V batteries to sell if a potential buyer has some qualms.

Also extra kudos: stuff like CAT cables with PoE or USB-C with PD could be set in various spots for modern accessories and consumer electronics, which is super cool.

So it may sound like I'm fairly settled on the question. But I think it's always good to rubber-duck debug stuff against other people's hears.

For background, I'm a software engineer with a decent background in electronics (I designed circuits, PCBs and built little machines however limited experience in power electronics). I've been researching the topic quite a lot over the last few months.

Accidental human contact with 48 Vdc in a wet and salty environment is far more dangerous than contact with 12 Vdc.

There are millions of boats on the water with 12 Vdc systems.

Not one tragedy I'm aware of, was due to the system voltage.

All were due to faulty wiring.

Faulty wiring on a 48 Vdc system, is 4 times more dangerous than 12 Vdc, for a given short circuit impedance, assuming the source can provide all of the current the circuit can take.

The advantage of higher system voltage is solely to reduce cable size.

This is why automobiles changed from 6 Vdc to 12 Vdc systems in the 50s and 60s; product cost reduction.

At some point, (such as in marine electric propulsion systems) 12 Vdc cables would become prohibitively large, and a higher DC system voltage may be warranted. But make no mistake, there are definite increased risks from increasing system voltage.

For this reason, for a typical 35 ft +/- cruising boat, a 12 Vdc system is optimal. Only if there will be unsually high DC loads, may a higher system voltage be justifiable against the higher cost (usually) components, and risk.

This is why most electrical safety standards have more stringent rules, for higher system voltages.

[tanglewood]

For things like a windless and capstain, you will need a pretty big 48V to 12V converter. You probably need what, 100A-200A for each device?



How will your alternator charge your 48V bank?


I love the idea of 48V, but think the cons still outweigh to pros at this point in time.

[aybabtme]

Originally Posted by ramblinrod

Faulty wiring on a 48 Vdc system, is 4 times more dangerous than 12 Vdc, for a given short circuit impedance, assuming the source can provide all of the current the circuit can take.

Respectfully, isn't assuming that there's no breaker in between. Bad wiring, as far as I understand it, is mostly a problem when high current loads are involved, leading to heat and fire due to improper connection between two components that heats up, starts melting and goes into a form of thermal runaway (the more it heats up, the more it burns material away, the less material is left to carry current, the more it heats up). Keeping a higher voltage and smaller breakers/fuses means the wires don't carry as much current, so less perfect connections are less at risk of burning up? And if there's short, the breaker/fuse will trigger. All this is based on the fact that higher voltage allows being a lot more stringent on the size of breakers and fuses.

Otherwise, why are people passing 120V AC alongside 12V DC? 120V in your body is going to kill you before 48V does. Why are people not blinking an eye at it, but saying that 48V is dangerous? And as far as I understand, AC has more ways to get into your body than DC, so in that sense for equivalent voltage, is more dangerous.

I'm trying to heed the warning about high voltage and dangers to humans, but I have a hard time buying this argument when put alongside people's counter-statement to use 120V AC. I'm probably missing a piece of the puzzle? Or maybe the conventional belief is wrong? Not sure, trying to figure it out.

[aybabtme]

Originally Posted by tanglewood

For things like a windless and capstain, you will need a pretty big 48V to 12V converter. You probably need what, 100A-200A for each device?

Honestly if I go ahead with a 48V storage system, I'd probably try to run 48V to the windlass. Then there's the bespoke replacement part syndrome problem showing up. Not sure. However, right now I have no windlass at all and pull my anchor by hand/with the hand cranked winch!

Originally Posted by tanglewood

How will your alternator charge your 48V bank?
I love the idea of 48V, but think the cons still outweigh to pros at this point in time.

Was thinking on charging it from solar/wind mostly and keep the engine connected to its own 12V battery, unchanged. I could also change the alternator for a 48V or higher voltage one. Obviously I'm still researching it all, hence my posting here. Haven't quite figured it all out!

[aybabtme]

Originally Posted by Dockhead

I think this is fallacious -- the load is the same as a percentage capacity of the cell, IF the battery bank has the same A/H capacity. Because at 4x the voltage, the cells will have 1/4 the capacity. So there is no gain at all here.

I'm more interested in kW/h than A/h. For 1kWh of battery at 48V, one only needs 20A/h. Spread over many cells, the amp per cell is 1/4 that of a 12V system. Meaning you can get batteries that are on the higher capacity/lower current side of the spectrum, which I find interesting.

Originally Posted by Dockhead

Concerning hard-installation of USB-C and POE sockets around the boat -- a warning -- this stuff goes out of date and out of fashion, but a hard installation will be there for possibly decades.

I'd make a specific enclosure for that, not cut through stuff. =) PoE is pretty common for a while now, in one version of the standard or another. Powering all my networking gear with this, it'd be super convenient. I honestly find this super exciting, but that's probably my hacker/thinkerer inclination.

[Lepke]

I have a 48v system. I have a power boat with lots of room so my situation is different. I decided on 48v for the inverter because I could have additional battery banks some distance away from the engine room and where the weight would do the most good for balancing out the boat. Also the savings in smaller cables and better choices in inverters. I use a MS-PAE Magnum that supplies 120/240v from the same inverter and can be ganged to 16kw. My goal was to be able to operate normally at anchor for 2 days w/o running a generator.
I use 12v only for emergency lighting, bilge pumps and electronics. I have a 48v alternator on one main that generally keeps up the batteries when running, so I no longer have a generator running, too. I save 1-2gl/hr by not running a generator and haven't seen an increase in fuel on my Detroit main since adding the 48v alternator. I schedule my generator running to making water and operating the water heater. My water heater sits on 2" Styrofoam and is surrounded and topped with 2" foam. It will hold high water heat for a couple days.
Another benefit is running large motors on 240v, so no expensive 12v motors and heavy cables. My windlass is 240v and so is the high pressure pump for the watermaker. I also have a large reefer and 2 freezers, all ac.

I don't find having 48v on board any more dangerous than having AC. And a lot less dangerous than propane.

[Dockhead]

Originally Posted by aybabtme

I'm more interested in kW/h than A/h. For 1kWh of battery at 48V, one only needs 20A/h. Spread over many cells, the amp per cell is 1/4 that of a 12V system. Meaning you can get batteries that are on the higher capacity/lower current side of the spectrum, which I find interesting.

I think you're missing the fact, though, that the cells are 1/4 the size.


So yes -- there is 1/4 the current. But since the cells are 1/4 the size, it's the same percentage of C. So the cells are working the same way. There is nothing to gain with this unless you increase the size of the bank.