Running two voltages - opinions?

[Spoonman]

Given that I have a boat where the entire electrical system is going to be replaced, mostly by me, I have the option to consider running 24 and 12 volt at the same time.

The boat is 48-feet so there is considerable distance from the batteries to the windlass (once I buy a windlass) plus I plan to have a few other items that draw a lot of current: radar, LectraSan, inverter, and auto-pilot (although I haven't done much research on these yet to know how much current they draw).

Since I'm starting from scratch, I have the option to set up my battery bank as 24-volt then use a DC to DC converter to make 12 volt. I realize there is some inefficiency in DC to DC conversion.

One advantage to using 24-volt for the high power stuff is that the wire size can be smaller by 1/4th which will save a little money, weight, and hassle of dealing with a stiff, thick wire at installation, but 24-volt stuff costs a bit more so if the only advantage is upfront costs, 24-volt might not be worth it.

Anyone have any experience with running multiple voltages? Is there any real advantage or am I just better off keeping everything simple.

Spoon

[donradclife]

With your size boat and power needs, its probably not worth the extra complexity of 24v. You can save a lot of money by buying the wire and fittings from Genuinedealz.com. Another consideration is the availability of 24 volt replacement motors/alternators/pumps/lights where you plan to cruise.

[Zanshin]

All boats that run 24V also run 12V. The big load items where 24V is an advantage tend to be the same price for 24V or 12V versions.

Do you have any electrics on the boat that you are going to keep - fridge, navionics (autopilot, gauges, etc.), water and bilge pumps? If yes, then I'd just get a battery or two forward to keep the high-power run to the windlass and bow-thruster short and then charge those batteries with a trickle feed (thin 12v cable). That it typical of under 50 footers and is also what I have on my boat.
If you start from scratch then go for 24V (even then, you might want a battery forward for the windlass) and keep just small batteries for the engine and genset starter at 12V and run the VHF off a 24-12V supply (which also keeps the voltage from spiking). Electric winches, SSB, refrigeration, inverter, autopilot and other big drains are all available as 24V systems.

I took a quick look at a Hallberg-Rassy last week and gasped (literally) when I opened up the breaker panel and saw --- nothing!!! The new Hallberg-Rassy boats are doing what should have been done years ago with boat electrics - they have gone to a CAN-bus system that saves a lot of heavy wiring (since power runs off a single backbone) and allows simple remote installation of devices without having to wire things. In this case, they used a standard Netgear wireless router. The purists will denounce this level of complexity, but if the CAN-Bus fails one can always manually trip the remote breakers.

[Spoonman]

On this boat I have nothing. It came with everything removed which makes it a great project boat: I don't have to take the old stuff out. Since there are no electronics to preserve, I have the option to go 24v on the big stuff. And, I do like the idea of the 12v coming from a DC - DC converter in that the 12v will be rock-steady at 12 volts pretty much all the time.

Thanks for your input. I remain interested in more replies...

Spoon

[goboatingnow]

I have a dual 24 and 12v system. It has its plus and minus points, Firstly The system batteries ( doemstic and starting are all 24V). So the 12V is mainly for instruments and the like. It can be hard to get 24V versions of things , and as a result I have 6 DC DC convertors, mostly in the 2-6amp range. I wouldnt reccomend a single big DC DC unit, very inefficient and one point of failure.

In retrospect the advantages of a common 12V system outway the 24/12 system and its why most boats are now 12V

Dave

[oceanscapt]

Having captained and currently captain a multi-DC voltage boat, I think the headaches and complexity outweigh the benefits. My current ride is a 1973 vintage and the owner likes the look of the old (and still working) gear.

My suggestion would pick a voltage that does as much of the heavy lifting as you can. The virtue of 24VDC is that the current loads are half, the wiring size smaller, all at the expense of somewhat limited choices on gear.

[LeftCoast]

For my boat I'd stay with one voltage myself, just to keep things simple.

But, for bigger craft, what about this idea?

I'm betting you aso have an inverter on this machine. So it would actually be three voltages 12, 24 & 120AC. Why not just run 120VAC like a high power trunk line down the boat? Much more efficient power transmission. Then all you need is the appropriate power supply near the equipment in question. Power supplies are plentiful with a wide variety to choose from.

I've never tried this, and it might be just crazy-talk, but it might be worth thinking about?

-jim lee