48V as main DC voltage on boat - anyone?

[oleman]

Actually going to 48 VDC just adds complexity to the system. We operate an over the road bus an MCI 9. Most electrical runs on 24 volts including the AC condenser and evap blowers BUT most of the exterior lighting is running off of 12 V. It has 2 Group 8 batteries in series for the 24v loads (the Detroit 8V92 starts on 24V) and 12V loads are run off of one battery. The 115V AC inverter runs off of the AC mains in a station or 24V on the road. The charging system is a 350A engine oil cooled alternator running at 24V to run the heavy I load and to charge the series batteries. (you do not want to purchase one of these) You guessed it, there are 24V interior lights and 12V lights. The PA system runs from 12 V. Working on the elctrical system is a PITA.
Many commercial battery backup system for electronics runs on 48 VDC BECAUSE that is a standard going back many years to the old telephone pulse relay systems that ran on 48 V. The commercial vessels I have been a crew member on have no DC power distribution outside of the equipment.
rack. Most shipboard equipment is powered by 3% 440 60 HZ.
Most Electric warehouse trucks and the Zamboni ice groomers do run off of 48VDC.

[Zven]

Here is one aspect that would probably not be an issue: Lights.
24V light bulbs are easy enough to find, LED or otherwise...
So just connect two in series, everywhere some light is required.
Red and green lantern goes in series, for example.
Viola, all lighting is 48V :-)
The same trick might even work for some other equipment .. E.g two bilge pumps. Could get complicated though :-)

[cyan]

Originally Posted by mvmojo

DC current is extremely dangerous... and not just in terms of an electronic shock. 30 volts dc and above can stop your heart! This alone is enough reason to avoid >24vdc systems!

Safety...

Actually, all current (AC and DC) is dangerous across your heart- and it's ALL about the current. Voltage and resistance just define how much current you'll get. AC current is actually more harmful to the heart, as fibrillation can occur. DC current can stop fibrillation (and normal heart beating) but can also cause muscles to "clamp on" more than AC.

Current (I) is indeed the killer, but higher voltage (V) poses the same problem as does lower resistance (R). I=V/R. Specifically, skin resistance is the big variable. Dry skin can have 100,000 ohm resistance. Wet skin can be 1000 ohms. (100 times less skin resistance means 100 times more body current for a fixed voltage) Salt water or sweat guarantees lower skin resistance. Most sources agree that 16-20mA heart current is the low threshold for possible death. The math is simple- 48V across two sweaty hands can result in 48mA across the heart. A quick zap is no big deal. A few seconds and your death is a coin toss. 12V across two sweaty hands will almost certainly not kill you. (careful with cut, bloody skin, though.)

My years working with 48V DC was with casual contact, and very little care. (or danger) This was typically in dry conditions, though. I would NOT feel as casual working in wet (boat) conditions on 48V DC. I did once vaporize a copper soldering tip across 48V DC contacts. A copper flash is spectacular to watch as fireworks from a distance. Different up close.

12V or 24V for me. The extra caution needed for 48V in wet conditions would be annoying IMO.

http://www.osha.gov/SLTC/etools/cons...eccurrent.html

https://en.wikipedia.org/wiki/Electr...hock_graph.svg

[witzgall]

Yes, I corrected myself later down the thread. The point I was trying to make, rather poorly, concerned the cross section of cable/wire. For example, see this tool, one I found when randomly searching via Google: DC Cable Sizing Tool - Wire Size Calculator - MM2 & AWG - solar-wind.co.uk

with the constants of:
3% voltage loss
10m of cable
20 amps of current

Selecting 24v specifies 16mm2 of cable
Selecting 48v specifies 6mm2 of cable, which is not 1/2 of the size, as many assume.

Is this pertinent to the conversation? Maybe not...

Chris

Originally Posted by Cadence

I think he just got his #s turned around.

Not to be cruel, but sometimes a little bit of knowledge is dangerous.

[ranchero76]

Originally Posted by TrentePieds

I think the more interesting question (than the one asked by the OP) is this:

What, precisely, apart from skinny wires, can the perceived incremental benefits of this higher voltage be for a mere yot?

All considerations taken together, I would think that such an "improvement" would make Willy Occam spin in his grave!

TP

I agree that in all less dangerous locations 120V AC or 240V AC can and should be used. Dangerous? Messing with different equipment throughout my life and been struck by 120V and 220V quite few times, I can confirm - yes, it's dangerous. But isn't floating in the little fiberglass tub with stick in the middle of ocean by far more dangerous thing?

If talking about big catamaran with huge solar setup (3-5kW) and huge Lithium bank (50-80kWh), benefits are:

- Main idea - to have 48V battery bank, and have as many things run without inverters as possible
- Smaller wire gauge throughout the boat
- Not having extra batteries here and there (starters and bow thrusters can run from main battery bank)

So actual idea is to simplify system, not to make it more complicated. For all critical equipment spare motors can be made/purchased at the time of building (and use SAME kind of motors with adapters in as many places as possible!), so replacing of broken motor can be done as easy as 1-2-3.

In my life I had quite few things with non-standard equipment. For example, Dodge Caravan with VW diesel in it and quite few custom made pieces to make it work. Like custom axle shafts, mounts etc. And I had to deal with that.
Replacing broken axle shaft took much longer, but I've learned many things in process. Same with transmission mount. Wiring was real nightmare, but still, I've managed to troubleshot and repair it. And you know what? I loved that van, because it was made the way I want it!

That's funny how scared people became of "non-standard things" in most parts of the World. I don't see much fun in living "standard life" with "standard things".

[ramblinrod]

Originally Posted by ranchero76

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.

What size of boat and what kind of loads are you contemplating?

Unless you have to deal with very heavy loads (like electric propulsion), this would be a total waste of time IMHO.

The majority of marine DC systems and appliances (and therefore the lowest cost) tend to be 12 Vdc. There are some dual voltage 12/24 Vdc products being developed, but still the majority and lowest cost are 12 Vdc.

Designing a system at a higher voltage, will reduce the size of cables required for some circuits. (The lightest cable per ABYC is 16 AWG with a few exceptions.)

So switching to 48Vdc for any circuits where 12 Vdc cables would be 16 AWG, makes no sense. Up to 12 AWG, the cable cost difference is virtually zero.

With a gas or diesel propulsion system, when you get to those high load devices like inverters, thrusters, and electric winch and windlass, a higher DC voltage will reduce cable size and cost.

One would have to do an analysis to determine if the cable cost saving would outweigh the cost of the higher voltage devices and appliances, switches, breakers, panels, and the DC - DC converter to operate all of the remaining 12 Vdc loads.

In my opinion, most likely no savings and a lot more hassle than needed unless electric propulsion or some very large loads aboard.

Prolly not worth any consideration on a gas or diesel powered boat less than 50 ft.

But if you are bound and bent to do it, why ask?

[TrentePieds]

Quote:"That's funny how scared people became of "non-standard things" in most parts of the World. I don't see much fun in living "standard life" with "standard things"."

Not "scared" - just fond of easy solutions to common, predictable but unavoidable and recurring problems. I have no doubt that you are able to cope with complexity. Even I can do do that, but why would I, when I don't have to?

In your OP you made a rather sweeping and absolute statement: that if building or refurbishing a boat - size and type not specified - you would use 48V. No reason you shouldn't, if that sort of deviation amuses you, but you didn't offer the "justification" of "needing" such a system for a seagoing condo. It'll be very hard to convince me that 48V is desirable, let alone necessary, in what I carefully specified: "a yot".

Now if you want to talk about boats, and ships, that have to earn their keep: tugs, fishing vessels, ferry boats, Ro-Ros and so on up to cruise liners and super tankers, then of course we are talking about a kettle of fish of a whole different colour :-)

I don't have a problem running #2 cabling from the pair of little 27 series antique-tech flooded jobs to my capstan. I don't have a problem starting my little three-banger off the very same paira deep-cycle antique-tech batts that keep me reading at night. I don't have a problem chucking out a coupla hunnert'n'fifty buck batts every three or four years and replacing 'em. Just preventive, like. I LOVE having Willy Occam aboard :-)!

IMO, in a yot, the incremental "benefits" of what you are proposing just ain't worth the complexity, the "trade offs", the potential hassle and the incremental expense. Mais à chacun son goût!

TP

[ranchero76]

Originally Posted by TrentePieds

It'll be very hard to convince me that 48V is desirable, let alone necessary, in what I carefully specified: "a yot".

I'm not trying to convince anyone to do anything. In OP I've asked if anyone have done this. I've got couple replies with useful information, the rest are just opinions of people who scared of anything non-standard.

My justification is given in same post you've quoted. I'm not saying that this will work for anyone. It depends on skills, ability and willing to work with custom things.

[Cadence]

Originally Posted by ranchero76

I'm not trying to convince anyone to do anything. In OP I've asked if anyone have done this. I've got couple replies with useful information, the rest are just opinions of people who scared of anything non-standard.

My justification is given in same post you've quoted. I'm not saying that this will work for anyone. It depends on skills and ability to work with custom things.

Most of the responses seem to be just a warning as to the financial ramifications.

[ranchero76]

Originally Posted by Cadence

Most of the responses seem to be just a warning as to the financial ramifications.

Believe it or not, the chance is 99% that I can adapt custom motor cheaper than OEM "off-the-shelf" motor. Example - for me, "off the shelf" electric motor for $1000 means only one thing - it DOES NOT exist. I will adapt cheaper alternative anyway, even if it would be 12V.

[StuM]

Originally Posted by witzgall

with the constants of:
3% voltage loss
10m of cable
20 amps of current

Selecting 24v specifies 16mm2 of cable
Selecting 48v specifies 6mm2 of cable, which is not 1/2 of the size, as many assume.
Chris

Slight miscalculation there
You are leaving it at 20A when doubling the voltage, so you are changing the power requirement from 480W to 960W

Keeping it at 480W (20A @ 24V, 10A @ 48V) gives you 16mm² and 4mm².

Of course, a lot depends on what you mean by "size".
A 16mm² wire is only twice as "thicK" as a 4mm² wire (2.26mm diameter v 4.52mm diameter)

And if you have unidentified wire, it's a lot easier to measure its diameter than its cross-sectional area.

[cyan]

Originally Posted by ranchero76

I've got couple replies with useful information, the rest are just opinions of people who scared of anything non-standard.

ranchero76,
You might have seriously misunderstood some of these posts. There are electrical engineers (such as myself) who have offered free professional advice, and who are certainly not scared of anything non-standard. Hell, most EEs LOVE the non-standard stuff. Thousands of volts are much more fun, anyway. I mean, why not simply connect the port toe rail to one side of 240V and the starboard toe rail to the other side? The wiring would be sooo easy and thin, and the motors would be quite common to replace in any part of the world! As a bonus the crew on the fore deck would be very lively in heavy weather, I think. (as long as you skip the GFCI)

[Dsanduril]

If you're looking for parts and information you might find this paper interesting:

48V/12V Dual Battery Automotive Systems

Some of it sounds like vaporware, or never implemented, but still a bit of an interesting read. The LTC3871 buck/boost unit is real hardware and available at DigiKey for small $.

[ranchero76]

Originally Posted by cyan

ranchero76,
You might have seriously misunderstood some of these posts. There are electrical engineers (such as myself) who have offered free professional advice.

Possibly to your big surprise, I do have University Degree as Electronics Engineer (do not mix with "electrical engineer"), including aerospace, radiolocation and other related stuff, so probably I can give you much more professional advise than you can give me. So I don't need any advise with that, all I was asking - if anyone who had done all of part of conversion, would share their experience.

[cyan]

Originally Posted by ranchero76

Possibly to your big surprise, I do have University Degree as Electronics Engineer (do not mix with "electrical engineer"), including aerospace, radiolocation and other related stuff, so probably I can give you much more professional advise than you can give me. So I don't need any advise with that, all I was asking - if anyone who had done all of part of conversion, would share their experience.

Fair enough. In the USA, a BSEE degree means an "Electrical Engineer", and also deals with electronics. Your country might use different terminology, but that's cool.

I honestly like your thinking. 48V is out of the box and this is a great forum for sharing experience.

However, you belittled those who were being helpful by writing that they were "scared". We can all help each other here without such denigration perhaps. No?
48V on a boat has some challenges, and why not explore them here? Some of us have done rocket science.
This isn't that.