48V as main DC voltage on boat - anyone?

[dkenny64]

if you're going to try running diesel electric?
say in a cat.. 2 electric motors? why are we even talking DC?
go to 3 phase AC 400HZ..motors are common..no capacitors..
smaller than 50/60HZ motors..

as for 48V LED lighting..no problem..
12-36v other equipment..I think most newer electronics are made for this anyway..

high current loads...3phase AC..400HZ..

harder to find the inverter to take the 48v battery bank back to 3phase AC at 400HZ..or should that be a 48Vdc motor running a generator a phase AC-400HZ??

for sure some thoughts above are absurd on a small boat? but what size boat was the OP question directed at? but if you want to think outside the box..

-dkenny64

[BlackHeron]

Originally Posted by StuM

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.

Build the boat around it. The electric drive motors will take up very little room so the engine rooms can be tiny. The traction batteries will need to go somewhere too. It's a legitimate design exercise.

Twice the power regeneration going with two motors when sailing too, or when anchored in a current.

And the 1.5kw was a typo. I meant 1.5 MegaWatt -oops.

Still pretty easy to site too actually. Did two of them on one site once, 3MW total, 13.8KV primary. CUNA Credit Union world headquarters, co-generation system linked with Madison Gas & Electric utility.

[ranchero76]

Originally Posted by BlackHeron

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.

When I mentioned 100-150kW diesel, I had in mind emergency situations, when long range full power motoring might be required. There's another factor - - even if whole EP system will fail (lightning strike, for example), sailor still might be lucky able to start diesel and go home.

Now, how cheap, light and "easy to install" will be 100kW diesel generator for serial system, to match performance of parallel system?

[nebster]

Dunno if it's helpful, but I retrofitted my wheeled boat to a 48(52)VDC battery recently. No propulsion/traction is in play, so no interesting motors or windings to discuss, though.

The only load the battery pack supplies is a very large inverter. Everything else, including the substantial 12VDC loads, are supplied and/or regenerated on the other side using AC-DC supplies. There is capacity for 15kW continuous demand and 30kW peak, drawing ~600A at 52VDC. The whole 52VDC side is floated with respect to the rest of the power distribution systems.

Btw, this is a test run for a catamaran ESS one day.

Some of the comments upthread about 48V safety are, in my opinion, right on. However, I don't believe there is any magic "touch-safe at 48, dangerous at 52" to be had. 48VDC is dangerous, plain and simple, and I prefer to treat it like line level power... except arcs are worse and even harder to quench.

I would not want a substantial 48V power distribution topology with the way things are built and wired today... and much less so in a wet, salty environment. A few carefully-controlled point-to-point runs for specific high-demand purposes, yeah maybe. Anything more really starts to feel like a science project and suffers from rapidly diminishing returns.

If you want to ping me off-thread, I can share some more details and thoughts.

[ranchero76]

Originally Posted by nebster

Some of the comments upthread about 48V safety are, in my opinion, right on. However, I don't believe there is any magic "touch-safe at 48, dangerous at 52" to be had. 48VDC is dangerous, plain and simple, and I prefer to treat it like line level power... except arcs are worse and even harder to quench.

Electricity is dangerous thing by default LOL ))
I remember, in high school we had lab with 42V AC outlet on every table.
Back then it was considered safe (or at least, not deadly dangerous) for kids )).
Of course 48V not meant to be safe to test with wet hands or handled by idiots. Whole modern world transformed to be safe for idiots, to the point when common sense does not exist anymore.

I've sent you PM.

[Pelagic]

Good post nebster[emoji106]

[nebster]

Originally Posted by ranchero76

Electricity is dangerous thing by default LOL ))
I remember, in high school we had lab with 42V AC outlet on every table.
Back then it was considered safe (or at least, not deadly dangerous) for kids )).
Of course 48V not meant to be safe to test with wet hands or handled by idiots. Whole modern world transformed to be safe for idiots, to the point when common sense does not exist anymore.

Ha, ha!

Well, let me amuse you with another, perhaps less intuitive thought. I actually believe the risk exposure due to potential arc flash/arc blast is greater than the total risk exposure of direct electrical shock, when working with a substantial lithium battery pack.

While I can take simple steps that basically prevent me from ever physically placing my heart directly in circuit with the energized system (dry hands or not), I am klutzy enough that I cannot completely guarantee I won't short some of these cells when bussing, unbussing, or connecting 51.2 nominal volts of DC with wires elsewhere.

I use insulated tools, I wear PPE, and I try to work carefully and not work when I'm tired, but it just takes one unlucky drop or miss and those cells can dump an incredible amount of energy into some metal and turn it into a flying bullet of hot slag. Would that event likely kill someone? No, but it would be pretty easy to be very seriously injured.

So putting aside all the other intricate and interesting safety aspects (is AC more dangerous than DC at voltage x versus y, etc.), I urge great care with lithium cells. They are much more responsive than lead acid, and they are deceptively gentle and safe looking when there is just one 3.2v cell sitting there on the table.

[ranchero76]

Originally Posted by nebster

Ha, ha!

Well, let me amuse you with another, perhaps less intuitive thought. I actually believe the risk exposure due to potential arc flash/arc blast is greater than the total risk exposure of direct electrical shock, when working with a substantial lithium battery pack.

While I can take simple steps that basically prevent me from ever physically placing my heart directly in circuit with the energized system (dry hands or not), I am klutzy enough that I cannot completely guarantee I won't short some of these cells when bussing, unbussing, or connecting 51.2 nominal volts of DC with wires elsewhere.

I use insulated tools, I wear PPE, and I try to work carefully and not work when I'm tired, but it just takes one unlucky drop or miss and those cells can dump an incredible amount of energy into some metal and turn it into a flying bullet of hot slag. Would that event likely kill someone? No, but it would be pretty easy to be very seriously injured.

So putting aside all the other intricate and interesting safety aspects (is AC more dangerous than DC at voltage x versus y, etc.), I urge great care with lithium cells. They are much more responsive than lead acid, and they are deceptively gentle and safe looking when there is just one 3.2v cell sitting there on the table.

Being working quite few times on live 120V and 240V circuits (including touching some wires accidentally and seen some scary sparks as well ))), I have to admit - you HAVE to be careful ))

On other hand, 1.3 million people killed in car accidents EVERY YEAR worldwide. Electricity? For example, electrical hazards cause around 300 deaths and 4,000 injuries each year among the U.S.

That means that cars infinitely more dangerous for people than 48V or even 240V voltage. If we are talking about safety here, cars must be prohibited immediately worldwide, no one should even touch them!

To some members here - just remember, next time you will open car's door - you're taking risk infinitely higher comparing to even having 240V voltage on your boat. Now you have to live with this till rest of your life. I know, it's terrible.

[Pelagic]

... How many people are working making high voltage electrical connections daily, as opposed to commuting to work in thier cars?
... Silly comparison!..

[ranchero76]

Originally Posted by Pelagic

... How many people are working making high voltage electrical connections daily, as opposed to commuting to work in thier cars?
... Silly comparison!..

How many people are using electrical high voltage appliances many times daily and *probably* risking their lives? Much more than drivers in the whole World!
On other hand, even on the boat no one works on electrical connections daily, let alone working on live wires! When I was young I was taught not to touch live wires, especially with wet hands. May be I'm too old and things changed since then...Or may be rules on the boat are different...
Stupid people will find a way to kill themselves no matter how hard you will try to protect them.

[valhalla360]

Originally Posted by BlackHeron

Build the boat around it. The electric drive motors will take up very little room so the engine rooms can be tiny. The traction batteries will need to go somewhere too. It's a legitimate design exercise.

Twice the power regeneration going with two motors when sailing too, or when anchored in a current.

And the 1.5kw was a typo. I meant 1.5 MegaWatt -oops.

Still pretty easy to site too actually. Did two of them on one site once, 3MW total, 13.8KV primary. CUNA Credit Union world headquarters, co-generation system linked with Madison Gas & Electric utility.

1.5MW works our to around 2000hp...For your typical 40-50' sail catamaran, that's probably a little bit of overkill.

Assuming you are replacing a pair of 30-70hp diesel motors, You are going to need similar but slightly larger diesel generators and on moderate sized cats, there is really one logical place to put them.

By the time you add in the electric propulsion motors, battery bank and the larger generator...it's going to be harder to fit everything in. Plus the conversion losses will kill any efficiency advantage.

That's where standard diesel propulsion in one hull and a small electric motor in the other work out well.
- If you are just tooling around the harbor for a sunset cruise at 3-4kts, you can run on pure EV.
- If you have a long run at 6-8kts, you run on the diesel...maybe supplementing within reason from the electric.
- The large battery bank gives you a limited redundancy but also allows you to consider major house loads run off the battery bank.
- Electric power can be obtained in a variety of ways (small generator sized for average not peak loads), alternator on diesel propulsion engine, solar array, etc...

Your typical 45' catamaran has two diesel propulsion engines and a generator. If you replace one of the propulsion engines with an electric motor and larger battery bank, it shouldn't add a lot to the up front cost, it can fit in the same locations and you lose very little motoring capability.

[StuM]

Originally Posted by valhalla360

Your typical 45' catamaran has two diesel propulsion engines and a generator.

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

[valhalla360]

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

And that's why I said "typical".

Go down to the local boat show and I bet you will be hard pressed to find a 45' cat on display without a generator.

So from a marketing perspective, Twin diesel propulsion and a generator is your baseline cost that buyers won't bat an eye at. If you can match the capability and cost while adding benefits, you have a product that will sell.

[OceanPlanet]

Originally Posted by ranchero76

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

Whoops, missed this yesterday.

14kW Polar Power genset. They now wish they had gone smaller and saved 100lbs.

One 10kW Electric Yacht (QT10.0) in one hull, and a QT20.0 in the other.

2 x 51V x 150Ah Lithionics battery packs, so 300Ah x 51V, or 15.3kWh

[OceanPlanet]

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'm with Stu...most of the cats we do now forgo the genset and use high power alts on the engines. Although these are usually lightweight high-perf cats where weight savings really matter.