48V as main DC voltage on boat - anyone?

[waterman46]

Originally Posted by witzgall

Yep, thanks for the correction. I should know better than to try and post here while doing our taxes.

So to summarize, moving from 24v to 48v would reduce the cross-section of a wire to 1/4 of the size, with a given load. the cross-section of a wire in a 48v system would be 1/16th of what would be needed on a 12v system.

Chris

Wrong math - the cross section AREA in 48V system can be 1/4 since resistance is directly proportional to cross-section area, but the same wire DIAMETER (not cross-section area) is therefore reduced by only square root of 4 = 2, compared to 12V system. 1/2 the wire size by measurement (not gauge).

[StuM]

Originally Posted by waterman46

Wrong math - the cross section AREA in 48V system can be 1/4 since resistance is directly proportional to cross-section area, but the same wire DIAMETER (not cross-section area) is therefore reduced by only square root of 4 = 2, compared to 12V system. 1/2 the wire size by measurement (not gauge).

His math was right.
<pedant mode>
"Cross-section" and "cross-section area" are synonymous.
Diameter tells us nothing about a cross-section unless the sectioned item is a solid sphere or cylinder
</pedant mode>

Wire size in most of the world is specified by "cross-section" or "cross-sectional area" in square millimeters. It's only the US that uses the strange logarithmic stepped AWG

Just to further complicate matters - the diameter of a specific AWG wire will vary depending on whether it is single or multi-strand

[Dsanduril]

Here's my use case for 48V, may be different than the OP's.

Right now there is a thread running here on CF about catamaran owners and running one or two engines when 'motoring' (we may have to find a new word once we get real motors involved). Seems somewhere down the middle between those who run two and those who generally only run one, turning on the second for maneuvering or bashing into some heavy stuff.

I fall into the 'run one' camp. There's a subset of that camp that has discussed ditching one of the engines and replacing it with a small motor/generator (MG) and battery bank, while also installing an MG on the engine side. This gives you a classic hybrid approach and lends itself very well to 48V. You could use the to MGs direct from the battery for getting into and out of the marina, never having to start the diesel (running the diesel for 10 minutes and then shutting it down is not good for the engine). When you want to motor for longer distances you still have the diesel (there really is nothing currently that matches the energy density storage of fossil fuels, so 'motoring' 500 miles on electricity is currently not feasible for most boaters - Turanor and its ilk as exceptions).

You lose the 'redundancy' of two engines, but you gain some flexibility. And with a 48V traction bank it then makes sense to use that for house power as well. Going whole hog you can install a variable pitch prop on the MG. Now you can motor very efficiently at 1kW or 10kW. And when the wind is up you can alter the pitch to decide how much drag you want to create charging the batteries back up. You have your own built-in, infinitely variable hydro generator.

That's not a dream, all of those components are readily available today. You can buy off-the-shelf hybrid systems exactly as described from any number of vendors. So why aren't anchorages full of boats fitted out that way? Because those of us that have looked into it seriously have found that it is cheaper and easier to put in a second diesel engine. There are a few outliers, the bleeding edge folk, and I applaud them for using these systems and helping the market grow, but for most of us this selection is cost prohibitive. Even for most DIY folk, although if you have the time and energy to scrounge really well it can be (and has been) done.

Now enter the automotive market 'mild-hybrid' model. Delphi (a huge automotive supplier) is looking to bring a fully integrated mild-hybrid setup to market at a USD$1500 price point (OEM price in mass quantity). That setup includes:

• A 10-12 kW MG
• A 1-2 kWh battery (likely some lithium chemistry - right now working with A123)
• A BMS for that battery
• A 48-12 DC-DC buck converter to power 12V auxiliary loads
• A small 12V battery that acts largely as a buffer for the buck converter

That's actually a drop-in setup that I could easily see porting from the automotive industry. At the target price point it is 1/10 or less the current cost of something similar. A few years after deployment the DIY crowd could find parts in wrecking yards. About the only change will be additional battery modules. Otherwise the BMS and system management software are already designed around proper maintenance of the battery, regenerative braking (the hydro generator), supplying heavy loads from the 48V bank, and supplying light loads (or those where conversion to 48V doesn't make economic sense) from 12V.

If such a system were on the market you would easily see windlass and thruster manufacturers offering 48V models. 48V automotive air conditioning (we don't have AC, but many boats now do) could be ported. With even mid-sized catamarans (in particular) now deploying 1-2kW solar arrays and with 'excess' speed available when sailing to run the hydro generator on cloudy days you might run the fossil fuel system only on rare occasions.

That's what I'm looking toward when I think 48V, and I love to see people like the OP and a few others I know looking ahead and going down the DIY/experimentation path.

Well, that's pretty long winded...

[ranchero76]

Originally Posted by Dsanduril

I fall into the 'run one' camp. There's a subset of that camp that has discussed ditching one of the engines and replacing it with a small motor/generator (MG) and battery bank, while also installing an MG on the engine side. This gives you a classic hybrid approach and lends itself very well to 48V. You could use the to MGs direct from the battery for getting into and out of the marina, never having to start the diesel (running the diesel for 10 minutes and then shutting it down is not good for the engine). When you want to motor for longer distances you still have the diesel (there really is nothing currently that matches the energy density storage of fossil fuels, so 'motoring' 500 miles on electricity is currently not feasible for most boaters - Turanor and its ilk as exceptions).

I love the idea, after couple years of studying related stuff I came to exactly same conclusion. There's actually more to it.
Having big solar on catamaran (5kW+) and big battery bank (let say, Tesla S 85kWh battery), it will give few more options like:

- At sea you can use ALL excess power you get to run one electric motor at low power (say 5kW), even while sailing, to gain speed (1 or 2 knots increase - doesn't matter, it's free!).

- No wind? It's not uncommon that many sailors prefer to wait for the wind instead of starting noisy diesels. With EP (assuming battery is charged) you can motor for a few hours, then you will have choice - to wait, or to start diesel, or maybe wind will be back by then.

And having electric motors in both hulls gives ability do not start diesel on ALL short trips - relocating the boat, in/out marinas etc.

[valhalla360]

Originally Posted by Dsanduril

Here's my use case for 48V, may be different than the OP's.

Right now there is a thread running here on CF about catamaran owners and running one or two engines when 'motoring' (we may have to find a new word once we get real motors involved). Seems somewhere down the middle between those who run two and those who generally only run one, turning on the second for maneuvering or bashing into some heavy stuff.

I fall into the 'run one' camp. There's a subset of that camp that has discussed ditching one of the engines and replacing it with a small motor/generator (MG) and battery bank, while also installing an MG on the engine side....

Once you add in propulsion, the rules really change a lot. Of course, with propulsion, the battery bank is usually near the motor, so a dedicated circuit for propulsion and a step down to feed house loads is still a viable and reasonable solution.

I'm really surprised manufacturers haven't taken this route for catamarans. It really does match really well with usage and if you can get it to replace the generator with a 2000-3000w solar array (and not severely restrict house electric usage), you can save a ton on either not needing or downsizing the generator.

I seriously doubt the $1500 figure for a drop in system will ever make it to the boating world. There is a world of difference repetitively building 50,000 cars per year using the exact same system and building 20 boats per year. Plus the battery bank necessary to make it viable on a boat will cost multiple times your $1500 number.

I still think it can make sense and with a good economical design, you can do it with little or no upcharge over a 2nd diesel but $1500 is overselling the idea when you consider the ancillary devices needed.

[TheThunderbird]

So.. The OP had to start this way:

"... Imagine a 5kW solar array on a large cat with a 50V output, .. Can l make an Intelligent use of it within a 50V system??"

Perfect if you consider electric prop. Weird if you want to run custom made 50V hungry appliances made for ships. Absurd for small 12V appliances.

est modus in rebus

[BlackHeron]

How about two electric motors and a diesel generator while they are at it? If they are going that route, might as well. Then at least power output curves would be matched for both props and hulls.

Then the generator and engine could be optimized for electrical generation and not needing to be placed on a saildrive low and close to the transom. It could be put whereever there is room in any orientation.

[ramblinrod]

Originally Posted by ranchero76

I've started this thread not to discuss options. It's simply wrong forum for this, too many sceptics kill any discussion on the spot - been there many times. I have my point of view and arguments, but rather would not discuss them here.
That's why I simply asked for first hand experience, if any.

(I need to heed my own advise that follows.)

I believe what is happening here, is that the original post, included what some may consider a controversial or provocative statement worthy of debate, in the very first sentence.

I myself posted a response that I believed would be valuable to you AND others viewing this thread.

In defense of myself and other posters here who have tried to contribute...

"Nobody can know, what you know, or don't know, until they learn so."

Now that you have declared that your are an Electronics Engineer, that is an indication (but not proof) that your do have fair knowledge of what you speak.

In future, perhaps avoiding provocative statements at the onset, and stating your question very clearly, will be more effective.

Here is your original post....

If I would be building (or rebuilding) boat, there's no doubt that 48V would be main DC voltage. There's at least one major reason for that - 4 times less current in all wires.

My question - is there someone on the forum who already done this and willing to share experience of converting to 48V? What were major difficulties of doing that? There are boats which came from factory with 24V system, but I never heard about factory installed 48V systems.

To me, the first sentence makes the post hypothetical; therefore I am not surprised that many responses were in kind.

Here is an example of a reworded post that may have been more effective.

I am a qualified electronics engineer, contemplating the design of a marine electrical system for a (boat description) to operate on a 48 Vdc system.

Here are the anticipated loads (1, 2, 3, n).

Here are the anticipated charging systems (1, 2, 3, n).

Here are the risks and benefits I have considered (1,2,3,n).

Can anyone who has personally done same, please share their experience and any difficulties encountered.

Then sit back, review the resulting responses, glean what you can, and disregard the rest that do not contribute to meeting your goals.

<<<<<<<<<<<< >>>>>>>>>>>>>>>>>

If you perceive this post above as unhelpful, please disregard.

[ranchero76]

Originally Posted by BlackHeron

How about two electric motors and a diesel generator while they are at it? If they are going that route, might as well. Then at least power output curves would be matched for both props and hulls.

Then the generator and engine could be optimized for electrical generation and not needing to be placed on a saildrive low and close to the transom. It could be put whereever there is room in any orientation.

In serial system you sure can have two powerful electric motors. But they will only provide very short range on full power, and I don't think it's a good idea to have 100kW generator on board to feed them.

In parallel system you can have one 100-150kW diesel. So in emergency situations you will have long range powerful diesel in one hull and electric motor in other hull, which will use as much power as boat can provide.

[Cadence]

Originally Posted by ramblinrod

(I need to heed my own advise that follows.)

I believe what is happening here, is that the original post, included what some may consider a controversial or provocative statement worthy of debate, in the very first sentence.

I myself posted a response that I believed would be valuable to you AND others viewing this thread.

In defense of myself and other posters here who have tried to contribute...

"Nobody can know, what you know, or don't know, until they learn so."

Now that you have declared that your are an Electronics Engineer, that is an indication (but not proof) that your do have fair knowledge of what you speak.

In future, perhaps avoiding provocative statements at the onset, and stating your question very clearly, will be more effective.

Here is your original post....



To me, the first sentence makes the post hypothetical; therefore I am not surprised that many responses were in kind.

Here is an example of a reworded post that may have been more effective.

I am a qualified electronics engineer, contemplating the design of a marine electrical system for a (boat description) to operate on a 48 Vdc system.

Here are the anticipated loads (1, 2, 3, n).

Here are the anticipated charging systems (1, 2, 3, n).

Here are the risks and benefits I have considered (1,2,3,n).

Can anyone who has personally done same, please share their experience and any difficulties encountered.

Then sit back, review the resulting responses, glean what you can, and disregard the rest that do not contribute to meeting your goals.

<<<<<<<<<<<< >>>>>>>>>>>>>>>>>

If you perceive this post above as unhelpful, please disregard.

Maybe to be crass? It sounded like someone who just discovered OHM's law?

[cyan]

Originally Posted by ramblinrod

(I need to heed my own advise that follows.)

I believe what is happening here, is that the original post, included what some may consider a controversial or provocative statement worthy of debate, in the very first sentence.

I myself posted a response that I believed would be valuable to you AND others viewing this thread.

In defense of myself and other posters here who have tried to contribute...

"Nobody can know, what you know, or don't know, until they learn so."

Now that you have declared that your are an Electronics Engineer, that is an indication (but not proof) that your do have fair knowledge of what you speak.

In future, perhaps avoiding provocative statements at the onset, and stating your question very clearly, will be more effective.

Here is your original post....



To me, the first sentence makes the post hypothetical; therefore I am not surprised that many responses were in kind.

Here is an example of a reworded post that may have been more effective.

I am a qualified electronics engineer, contemplating the design of a marine electrical system for a (boat description) to operate on a 48 Vdc system.

Here are the anticipated loads (1, 2, 3, n).

Here are the anticipated charging systems (1, 2, 3, n).

Here are the risks and benefits I have considered (1,2,3,n).

Can anyone who has personally done same, please share their experience and any difficulties encountered.

Then sit back, review the resulting responses, glean what you can, and disregard the rest that do not contribute to meeting your goals.

<<<<<<<<<<<< >>>>>>>>>>>>>>>>>

If you perceive this post above as unhelpful, please disregard.

THAT makes sense on so many levels, thanks for posting.
This awesome forum is great for gathering professional answers to layman questions. A bit of background up front will save everyone's time.

[OceanPlanet]

Speaking of 48V serial-hybrid electric systems, with 12V system battery backup...here is a system for a charter cat being done currently.

[ranchero76]

Originally Posted by OceanPlanet

Speaking of 48V serial-hybrid electric systems, with 12V system battery backup...here is a system for a charter cat being done currently.

Doesn't tell power of generator and EP. Judging by battery size, motors are small.

[BlackHeron]

Originally Posted by ranchero76

In serial system you sure can have two powerful electric motors. But they will only provide very short range on full power, and I don't think it's a good idea to have 100kW generator on board to feed them.

In parallel system you can have one 100-150kW diesel. So in emergency situations you will have long range powerful diesel in one hull and electric motor in other hull, which will use as much power as boat can provide.

Obviously. Where did I say use a tiny generator not capable of powering both motors at near full thrust? Why not just ave a larger generator then? Scale the silly flim-flam thing. It has to be easier/cheaper to install/mount a generator than it is to mount/align a motor and propshaft or even a motor and saildrive. I'm a commercial electrician. I've installed, set and wired gensets up to 1.5kw, and I've installed marine diesels. I can tell you that a genset is a much easier thing to site and mount than a marine diesel propulsion engine.

[StuM]

Originally Posted by BlackHeron

. I'm a commercial electrician. I've installed, set and wired gensets up to 1.5kw, and I've installed marine diesels. I can tell you that a genset is a much easier thing to site and mount than a marine diesel propulsion engine.

1.5kW? Sure a 1.5kW genset is simple to site and mount. Just stick it in a lazarette until you need to pull it out and use it.

When you are looking at replacing 80HP of diesel engine(s) and supplying house loads, You need more like a 50KVA generator as an absolute minimum. They are not quite as easy to site.