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Old 05-19-2018, 11:25 AM   #1
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12 volt vs. 24 volt

I've been viewing boat porn on Yachtworld and notice that some boats such as older Hatteras have 24 volt electrical systems. I'm clueless about electrical systems and I'm curious as to the pros and cons of these two systems. Hope you guys can educate me. Thanks, Howard
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Old 05-19-2018, 12:22 PM   #2
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24V electrical systems allow high amperage motors like starters and bow thrusters to work without requiring big heavy wiring. In some cases, like bow thrusters you can get higher hp/thrust with 24V.


Many lighter load devices are also made in 24V but some are not. There are a couple of ways to deal with this:


1. Have a separate 12V battery system with separate charger or voltage converter to power the 12V loads.



3. Use a clever set of relays to combine two 12V battery systems to produce 24 V but allow use of 12V for house loads.


So a 24V system has its virtues, but it will probably require more complexity to deal with the 12V loads.


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Old 05-19-2018, 12:46 PM   #3
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So a 24V system has its virtues, but it will probably require more complexity to deal with the 12V loads.
Disagree for two reasons: 1) virtually any marine item that you can think of is available in 24 volt a lot of electronics are dual voltage 2) voltage converters are very simple to install. I had two NewMars on my old Hatteras that converted 32 volt to 12, for instance and if I hadn't run across one of them at a surplus store super cheap, the OEM unit would have sufficed fine. Given the choice I would see a 24 volt boat as a positive vs a 12 volt boat. Heck, I liked all the 32 volt stuff I had on there. I had about every DC voltage under the sun on that thing.

By the way, you'll typically see (Magnum comes to mind) that higher wattage inverters are 24 volt.
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Old 05-19-2018, 12:53 PM   #4
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Some boats are all 24 volt; others have 24 and 12 volts. A second alternator to a 12 volt house battery bank makes only the engine and bow thruster needing to be 24 volts.
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Old 05-19-2018, 01:19 PM   #5
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Size of boat usually plays a lot in the decision in how its rigged voltage wise.
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Old 05-19-2018, 01:44 PM   #6
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When I spec'd my boat for construction, I gave consideration to a 24v system since the size of the boat, especially with the tower, lots of long runs were inevitable. The builder talked me out of it since the boat is intended to travel to distant places where 24v parts are harder to come by. So, I went with 12v without regrets.
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Old 05-19-2018, 01:46 PM   #7
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24V is no issue for high power items, motors, chargers, etc. Except that you will also require 12V.
You will have a hard time finding high volume electronics in the 24V class. DC stereos, HF or VHF. The RF power amps virtually do not exist to work with both voltages.

Furuno tends to have the best 24V dc support for FF, radars, etc. But, I think Icom, Garmin, Raymarine, not so good.

That then brings up the next point; do you need 120 or 240V ac, if you have 24V DC. If you need to "plug-in" to get energy, that generally means yes. So, now you are, at least, with a 24V, 12V, and 120V panel. And a larger vessel with 240V too. It can all be made to work, just a matter of $, and the ability to hire or work the complexity.
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Old 05-19-2018, 02:59 PM   #8
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Originally Posted by MYTraveler View Post
When I spec'd my boat for construction, I gave consideration to a 24v system since the size of the boat, especially with the tower, lots of long runs were inevitable. The builder talked me out of it since the boat is intended to travel to distant places where 24v parts are harder to come by. So, I went with 12v without regrets.
That's interesting. I'd think the same would apply to Nordhavn and Fleming boats, yet they are 24 volt OEM these days, with 12v available through converters for 12v equipment. Just to name two "designed for distant places..."

Most larger boats these days are 24v. By the way you can get 24v chargers that accept 120 as well as 240. I think you will also find that 240 is very common as well. I had a boat that had 240 and 120 and that wasn't complex to manage; the builder laid out the panels quite nicely. 240 was so much nicer for AC, pumps, and of course the all electric kitchen! And I like the idea of fewer amperes running around.
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Old 05-19-2018, 02:59 PM   #9
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My sailboat is 24V/12V. 24V for everything that could be, but there are some things that just aren't available (like the engine....) that had to be 12V. Those are all powered by 24-12V down convertors (3 of them). The savings in copper (money and weight) is substantial. Things tend to work a little better because a 1V drop in 24 is small compared to a 1V drop in 12, and less likely to happen at that (as they are drawing half the current).

I did have the problem mentioned above - in Port McNeill, BC the fridge circ pump went Tango Uniform and getting a 24V replacement was problematic. There were 12V ones on the shelf in town.

If I built the boat again, I'd still go 24V. If buying, I'd consider 24V a plus, not a minus.
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Old 05-19-2018, 06:38 PM   #10
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My sailboat is 24V/12V. 24V for everything that could be, but there are some things that just aren't available (like the engine....) that had to be 12V. Those are all powered by 24-12V down convertors (3 of them). The savings in copper (money and weight) is substantial. Things tend to work a little better because a 1V drop in 24 is small compared to a 1V drop in 12, and less likely to happen at that (as they are drawing half the current).

I did have the problem mentioned above - in Port McNeill, BC the fridge circ pump went Tango Uniform and getting a 24V replacement was problematic. There were 12V ones on the shelf in town.

If I built the boat again, I'd still go 24V. If buying, I'd consider 24V a plus, not a minus.
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Old 05-19-2018, 06:47 PM   #11
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I played and worked in the marine industry a long time. I’ve seen 6, 12, 24, 32 and 110 volt DC systems. If I was building a boat of any size today I’d go with 24 volt. The whole industry is headed that way now.

It will be interesting to see what happens to boats if the auto industry goes to 48 volt as I’ve been reading lately.
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Old 05-19-2018, 07:04 PM   #12
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The trouble with HV DC is the ability to break it with a cost effective circuit breaker. Also, relays and switches become more exotic. Search for a 20Amp breaker rated at 125V dc. $15 for 12/24, and about 50 to 100x that at 125.
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Old 05-19-2018, 10:39 PM   #13
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There are several devices that can reduce 24v to 12v. Many on ebay. Other voltages, too. In the old days most larger boats had 32 volt systems. The higher volt systems use smaller wire sizes (look up amps/wire sizes in a table) and are less prone to burning contacts or burning out motors. In one boat I had a 32v bilge pump that was 30 years old.

I use to have a WWII built tug that had a 250v DC system. Nothing ever failed.
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Old 05-19-2018, 11:37 PM   #14
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There are several devices that can reduce 24v to 12v. Many on ebay. Other voltages, too. In the old days most larger boats had 32 volt systems.

In one boat I had a 32v bilge pump that was 30 years old.

I use to have a WWII built tug that had a 250v DC system. Nothing ever failed.

One of my previous boats (1950's) was wired like that: 12vDC, 32vDC, 110vAC, 240vAC. Bilge pumps were the higher voltage also. It was a frustrating system on the surface but I have to admit everything was extremely reliable. Even the old transformer inverter ran flawlessly - stove, refrig, deep freeze.

The only thing I hated were those 12vDC light bulbs which were extremely expensive to find and replace.

However I would not wire my next boat like that - only 24vDC and 230vAC (50hZ).
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Old 05-20-2018, 12:01 AM   #15
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I agree that 24vDC would be first choice for a major refit or new boat. With some 24 to 12 transformers. Possibly a 12v battery for electronics, it would be a very stable power supply for anything sensitive.

But, I would also carefully consider 48vDC for a house bank. Off grid systems are usually this voltage, and HopCar indicates some car stuff is heading that way as well. The one wrinkle might be sourcing 48v alternators for the engines, and possibly sourcing an AC charger at 48 vDC as well.

Its the usual smaller wire size advantage, but another angle is solar. I have 2070 W of panels, and needed to install 2 x Outback Flexmax 80 solar controllers since they are limited to 80 A output to house bank. That's 80 A at 12v, or 24v, or 48v or even 60v. So, had my house bank been 24vDC I would have only needed one FlexMax. And if I had a 48vDC house bank then I could install twice as many panels as I now have. Er, where would they go?. Victron have 48vDC inverters. There would be minimal switching. Just fuses and an isolator, connections to alternators, inverter and solar controller. Then a transformer or two to keep 24v batteries for starting and 12v battery for electronics topped up. In this dream boat scenario reefer etc would be 230vAC powered. The house bank and inverter would be 'generously' sized.
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Old 05-20-2018, 12:34 AM   #16
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+1
Hey Delfin, you might remember our sailboat, we were tied up just behind you in False Creek last August (I think). 'Anomaly', a rather unusual custom cat yawl design in sky blue topsides.

Joining the ranks of power boaters, it is the right tool for the rainy and windless PNW. Sailing the sailboat south to where there's wind.

I love your boat by the way. Have admired it in Anacortes from time to time.
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Old 05-20-2018, 12:43 AM   #17
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Insequent, certainly 48VDC would be more efficient but starter motors are generally either 12 or 24 volts, which means two charging systems.

I have looked into a 3 phase inverter system which ran off of 3X4000 watt inverters. As I recall those were 24v or 48v supply as well.
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Old 05-20-2018, 07:07 AM   #18
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"The whole industry is headed that way now.(24v)"

25 years ago I would have agreed as the cost of thinner wire in millions of cars a year looked great.

So far only large trucks and bus engines use 24V , for starting & running their electronic injected engines.

The usual setup is a Vanner equalizer , which makes 65 or so amps of 12V for lights radios etc.

A 24V alt in no problem for a big house bank, but the radios , lights and marine interior toys still need 12V , or it becomes expensive.
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Old 05-20-2018, 07:34 AM   #19
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In my work I do a lot of DC to DC conversions. Power stations like to use 125V dc, sometimes 230V dc. My uProcessors need 3.3V and 1.8V. My small relays need 12 or 24V. And, so it goes. Many conversions to deal with. It is all doable with mostly off the shelf circuits. But, $ is a function of watts. If you need to power a 12V VHF, and are handed 125V, that conversion brick needs to handle 5Amps or so, and costs $. For each item, the total conversion costs goes up. Each conversion reduces reliability, may cause electrical/RF noise generation, waste heat, and reduced surge protection.
It is still worth the exercise in may scenarios, especially when weight is a large factor. If your device has to leave the ground, if lots of stops and starts, if you need a HV traction motor for a EV, for instance BUT, a trawler?? Copper IS heavy, takes up room, but is very reliable.
You will be sad if even a close lightning hit takes out all/most of your conversion technology.
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Old 05-20-2018, 10:51 AM   #20
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One thing I liked about the NewMar converter is the output voltage regulation. They are spec'd to be within 1percent over a wide range of input volts.
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