12 volt vs. 24 volt

[hmason]

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

 

[DavidM]

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.


David

 

[caltexflanc]

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.

 

[O C Diver]

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.

 

[psneeld]

Size of boat usually plays a lot in the decision in how its rigged voltage wise.

 

[MYTraveler]

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.

 

[diver dave]

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.

 

[caltexflanc]

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.

 

[DDW]

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.

 

[Delfin]

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.

+1

 

[HopCar]

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.

 

[diver dave]

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.

 

[Lepke]

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.

 

[Mako]

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).

 

[Insequent]

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.

 

[DDW]

+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.

 

[Mako]

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.

 

[FF]

"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.

 

[diver dave]

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.

 

[caltexflanc]

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.

 

[Ski in NC]

It mostly comes down to engine starters. Get to a certain engine size, around 12 liters and up and a 12v starter gets too big to fit on the engine. So they go 24v. Ok, now starter is 24v, so need 24v batts and alt, or a series/parallel relay (PITA). How far to carry the 24v? Whole boat (PITA)?

If engine needs 24v start, I prefer a 24v start bank and a separate 12v house bank. Only because of the hassle of sourcing 24v things like pumps and lights.

If EVERYTHING could be sourced in 24v, that would be awesome and I would happily set the whole boat up for 24. But not there yet. Most easy to find stuff is still 12v.

Oh and talking about PITA? Let's talk 32V!!

 

[DDW]

If you suffer a lightning strike, the converters will be the least of your worries. On my boat, the only things needing 12V were a few of the smaller instruments (chart plotters, radar, etc are routinely available in 24V), the ITR diesel heater, and the engine. There are 3 DC-DC convertors, each producing 10A: one for the instruments, one to charge the engine start battery and run the engine, one to power the diesel heater. In 10 years, one of those has failed (diesel heater), not due to an internal problem but heating at the terminals which were not tight enough. One can always jump the batteries to get 12V in a pinch. The lighting, winches and windlasses, running lights, entertainment system, autopilot, MFDs, radar, communication equipment (except the VHF), pumps, charger/inverter, are all 24V.

I don't think a 24V or split system is significantly less reliable, and due to most of the currents begin cut in half it can be argued that it will be more reliable.

 

[diver dave]

If you suffer a lightning strike, the converters will be the least of your worries. On my boat, the only things needing 12V were a few of the smaller instruments (chart plotters, radar, etc are routinely available in 24V), the ITR diesel heater, and the engine. There are 3 DC-DC convertors, each producing 10A: one for the instruments, one to charge the engine start battery and run the engine, one to power the diesel heater. In 10 years, one of those has failed (diesel heater), not due to an internal problem but heating at the terminals which were not tight enough. One can always jump the batteries to get 12V in a pinch. The lighting, winches and windlasses, running lights, entertainment system, autopilot, MFDs, radar, communication equipment (except the VHF), pumps, charger/inverter, are all 24V.

I don't think a 24V or split system is significantly less reliable, and due to most of the currents begin cut in half it can be argued that it will be more reliable.

Interesting that your largest current device (starter motor) is 12V and most of the rest of the boat is 24. Yes, as you increase voltage, the reliability goes up. Signaling in a power station is often 125V dc, due to the ability of a higher voltage breaking down oxides in little used alarm contacts and connectors.

Any issues I have with system reliability are centered around the several convertors that seem to be the necessary evil. I witness lab work wherein electronics is blasted with RF, surges, dropouts, brownouts, humidity, temperature extremes; all kinds of related mayhem. I have seen the voltage output from inverters go wildly out of control with certain stimuli. Yes, it can all work. My advice is to check the specs carefully.
Copper wire, so far, is immune to anything I can dish out.

 

[hmason]

Thank you all for the amazing input. I'm no longer afraid of a boat with 24v.

 

[caltexflanc]

It mostly comes down to engine starters. Get to a certain engine size, around 12 liters and up and a 12v starter gets too big to fit on the engine. So they go 24v. Ok, now starter is 24v, so need 24v batts and alt, or a series/parallel relay (PITA). How far to carry the 24v? Whole boat (PITA)?

If engine needs 24v start, I prefer a 24v start bank and a separate 12v house bank. Only because of the hassle of sourcing 24v things like pumps and lights.

If EVERYTHING could be sourced in 24v, that would be awesome and I would happily set the whole boat up for 24. But not there yet. Most easy to find stuff is still 12v.

Oh and talking about PITA? Let's talk 32V!!

I never had any hassle sourcing 24 or 32 volt stuff on the east coast of the US as of three years ago. I had 32v dc lights of all sizes and shapes, fresh water pump, bilge pumps and switches, starters, alternators, windlass motor, solenoids etc etc. On 24volt, inverter, bow thruster, electronics suite (Furuno). Since we cruised full time and preferred life away from the dock, we did carry a variety of spares. Maybe 32 has worsened but I'd wager 24 has got better.

 

[DDW]

Interesting that your largest current device (starter motor) is 12V and most of the rest of the boat is 24. Yes, as you increase voltage, the reliability goes up. Signaling in a power station is often 125V dc, due to the ability of a higher voltage breaking down oxides in little used alarm contacts and connectors.

Any issues I have with system reliability are centered around the several convertors that seem to be the necessary evil. I witness lab work wherein electronics is blasted with RF, surges, dropouts, brownouts, humidity, temperature extremes; all kinds of related mayhem. I have seen the voltage output from inverters go wildly out of control with certain stimuli. Yes, it can all work. My advice is to check the specs carefully.
Copper wire, so far, is immune to anything I can dish out.

I've let the smoke out of a lot of copper wire in my day. It's like alchemy: the copper disappears and smoke appears in its place.

I'd have liked to change out the starter motor, but could not find one that fit so it would have had to be rewound. Anyway, the engine has its own start battery, the rather limited electronics on the engine (75 hp Volvo auxiliary) were 12V so I stuck to it. There are other higher current consumers on the boat: the windlass takes about 100 A @ 24, the power winches around 80 each @24, the invert up to about 150A @ 24 - all of which would have been twice that on 12 and all of which have much longer cable runs than the starter.

The big challenge would have been the alternator, spec'd at 280A @ 24V (7 KW!) - not even sure that would be possible at 12V. As it is we used 4/0 cable.

 

[diver dave]

...

The big challenge would have been the alternator, spec'd at 280A @ 24V (7 KW!) - not even sure that would be possible at 12V. As it is we used 4/0 cable.

Wow, impressive on a little diesel.

Must be quite the bolted connection on that baby!
Belted drive?

 

[DDW]

No, for belt drive you'd need a K8 and 180 deg of wrap, even then there'd be dust. I drive it with a shaft, home made. An adapter on the damper pulley connects to a Vetus Bulflex prop drive, then a short shaft, then another Bulflex, then the alternator. The Electrodyne alternator has it's own mounting bed, it weighs about 1/4 what the engine does and takes about 15 hp to drive it at full output. The Bulflex drives have rubber in them to isolate the 4 banger torsional vibration from the alternator and take up the engine movement. I originally had a Spicer U joint on the alternator end, but the vibration got to it after about 700 hours, so I replaced it with the second BulFlex. The Electrodyne is a unique design, the only moving part is a toothed steel wheel, no rotating coils at all, no brushes. I've seen it put out 300 amps measured on the shunt, and it does that at 2000 shaft rpm (no belt so it runs at engine speed). Their scheduled maintenance suggestion is to regrease the bearing every 20,000 hours.

The second alternator is a Balmar that will do about 50A @ 24V. The K6 belt has only about 90 degrees of wrap, and it generates plenty of belt dust.

 

[johnrupp]

No, for belt drive you'd need a K8 and 180 deg of wrap, even then there'd be dust. I drive it with a shaft, home made. An adapter on the damper pulley connects to a Vetus Bulflex prop drive, then a short shaft, then another Bulflex, then the alternator. The Electrodyne alternator has it's own mounting bed, it weighs about 1/4 what the engine does and takes about 15 hp to drive it at full output. The Bulflex drives have rubber in them to isolate the 4 banger torsional vibration from the alternator and take up the engine movement. I originally had a Spicer U joint on the alternator end, but the vibration got to it after about 700 hours, so I replaced it with the second BulFlex. The Electrodyne is a unique design, the only moving part is a toothed steel wheel, no rotating coils at all, no brushes. I've seen it put out 300 amps measured on the shunt, and it does that at 2000 shaft rpm (no belt so it runs at engine speed). Their scheduled maintenance suggestion is to regrease the bearing every 20,000 hours.

The second alternator is a Balmar that will do about 50A @ 24V. The K6 belt has only about 90 degrees of wrap, and it generates plenty of belt dust.

I'd like to see a picture of your homemade setup,

 

[DDW]

Photobucket eliminated all my online library of photos with their extortion tactics. Starting again with imgur.

Here is the general engine room arrangement, saildrive with alternator to the right:

This is the original shaft (disconnected at the engine side in this picture), Bulflex on the damper pulley, Spicer spline shaft for extension and U joint on alternator:

That started to come loose in Maine on the trip south from Newfoundland, so I took it home, cut the U joint off and welded on another BulFlex. That required a peculiar adapter on the alternator shaft to make it look like a prop shaft:

New version installed. The extra stainless bit is intended to carry a guard to keep your arms out of it, but mainly to catch the shaft in case it breaks loose from the alternator end, and beats a hole in the bottom of the boat:

The Bulflex can move a little both in angle and in length. U joints (and CV joints) have to be kept slightly misaligned to keep them from Brinelling, the Bulflex doesn't, plus it has the vibration dampening.