Switch to 24V or 12/24V Hybrid Electrical System

We don't own a trawler right now, but that hasn't stopped some pretty extensive day-dreaming about what is the best energy independent (of land), quiet, and efficient power system possible.

The most interesting idea (not new) I've had so far is to switch from a purely 12v system to a 12/24v hybrid or even pure 24v system. Here's a really good synopsis I found of the advantages & drawbacks of the various electrical systems available: http://www.polardcmarine.com/downloads/Onboard_Power_Systems3.pdf.

I would get rid of the AC generator and go to a DC high output (say 300-400A) alternator driven by a small water-cooled diesel engine like this: Marine Micro-Cogen for recreational and commercial vessels (I'm using these links not to advertise this company, but because they have really helped me learn about this stuff). The small engine in place of the large AC generator allows more room for batteries and it's low hp means it will be working in its happy load range, as opposed to the AC generator loafing, wasting fuel, glazing its cylinders, and charging the house bank too slowly. Same for using the propulsion engine to charge the house bank (even with a big alternator on the propulsion engine)--much more efficient use of diesel fuel to charge the house bank, no underloading the engine.

A large 24v housebank (say, 1500 amps), solar panels (on the pilothouse roof of a KK42 for instance) and wind generator would extend the time intervals where the very quiet little DC generator would be needed. Paralleled 3000watt true sine-wave inverters would handle the 110v duties where necessary (e.g., you bought a cheaper 110v RV type fridge due to budget constraints). 24V reduces your wire size alot and really increases the efficiency of whatever appliances you might get (fridge, freezer, anchor winch, thruster, starter motor, etc.). You can always get local down-converters for say your 12v nav & communication equipment. Complicated?--perhaps, but I think a reliable system can be created where the various charging systems work harmoniously together. I'm sure it has been done before--there must be a lot of off-grid houses with this kind of setup.

A long intro to the question, but here it finally is: has anyone switched from a 12v to a 24v or 12/24v hybrid boat electrical system? I realize the capital outlay for this system is large (especially a 1500A, 24v AGM or TPPL housebank!), but even if it doesn't pay itself back in hard financial terms, the increased reliability, comfort, and quietness due to minimal generator runtime means alot imo. The goal is lots of power with maximized quiet times.....

Feasible? Not even?

Rgds,
Wil

No, haven't switched out, it get very expensive, but have given it a bunch of thought, since as you will see I became master of many voltages (or should I say, they of me!) The Hatt is a 32 volt boat; I left all the baseline stuff that way (starters, alternators, DC freshwater pump, bilge pumps, DC lights, to name some majors), used 12 volt converters for stuff like electronics. The came to me also with a 24v thruster powered by two 8ds, a 12v started generator. When I added the inverter and its bank, went with 24v for a variety of reasons. But the basic thing is, I never felt it made sense to change anything for the sake of change. I promised myself the next boat would ideally all be 24 volt, but changing stuff out for the sake of doing it makes no economic or use-of-time-sense.

Some people advocate an approach similar to what you are proposing, I like the idea of a DC generator. Since you are in the study and theoretical mode. Let me give you a couple more sources: first, despite an awfully formatted web site, very dense with information and quite knowledgeable:

ZRD Electric Designer OEM - Your Source for DC Generator, Alt, ...

But first, get yourself a copy of Nigel Calder's "Boatowner's Mechanical and Electrical Manual". You'll need it when you get a boat and in the meantime it will educate you about all this stuff and more in easy to read and very thorough fashion.

Good reading!

Unless you are trying to drive your boat with electricity, then there isn't anything you can't do in 120 VAC and 12VDC with a small AC genset, a reasonable size battery bank- say 400 AH and a 2,000 watt inverter/100 amp charger.

Your DC wiring will be bigger than a 24V system, but there are really only two big amp consumers: the starter and the inverter. All else is 6 gauge or smaller.

And this system is the cheapest and easiest to make work. No DC/DC converters or changing out DC motors to work with 24V. Even solar panels can easily be used with 12V. Yes it takes a bigger amp controller and a size or two bigger wire, but the cost is small compared to all of the things you have to do to work with a 24/12V DC system.

And you have AC to drive your A/C.

Dreaming is fun, but practically and cost effectively it doesn't make sense to have a DC only system with 24/12 V.

David

George, I don't believe in change for its own sake either. It does seem to me that the advantages to be gained by 24v are substantial, though really expensive. Probably the only thing I would actually do early with my boat is convert to a DC generator, inverters, and more batteries--just don't like the sound of an AC generator running every time I need to cook (that will probably be propane anyhow, though diesel stoves are getting better Wallas Heater | Boat | Stoves | Cooking Equipment | ScanMarineUSA.com | Wallas Heater | Boat | Stoves | Cooking Equipment | ScanMarineUSA.com), play the stereo, or microwave something.

I do indeed have a copy of Calder's book, it has been the starting point several times on questions that came up. And thanks for the ZRD website, good stuff that, it will be great reading fun.

Cheers,
Wil

Hi Will,

My N47 is a 24 Volt Boat with a large house bank ( 8 8d AGM's ). The only real disadvantage is that it is sometimes more difficult to find 24volt parts when something breaks. That just means it's prudent to carry spare 24volt pumps and other parts that might be hard to find.

I do have to maintain a small 12V bus for some of the navigation gear and the Wallas Furnaces, but most modern navigation equipment is happy running on 24 volts.

We are also a 24 volt boat and do carry a spare 24 volt water pump but I'd carry a spare freshwater pump anyway even if it was 12 volts. My pilothouse and flying bridge are hybrids just because of the electronics. I have a small breaker panel just for the 12 volt stuff.

Dave

Well David, I guess that's a vote for "Not Even?". I should have been clearer in the premise: I don't like AC and would rather not have it on my boat (except of course in sine wave inverter form where AC is needed) if DC will fulfill the power requirement. We'll agree to disagree on that one.

Battery, inverter, and DC charging (incl. wind, solar) & regulating technology is getting to the point (and closer to the price point) where it is feasible. 12v is inherently less efficient and reliable than 24v in every way. For example, the same difference 6v starter motors were to 12v starter motors.

An advantage to the 12/24v hybrid system is you can run your electronics off the 12v bank and so keep all noise out of their power, as the charging happens in the 24v bank. No DC converters needed.

Naysayers give valuable input, but I would really like to hear from anyone who has actually done it partially (thanks George) or fully and their thoughts on the process. Interesting ideas on how it could be done, rather than 'no, don't' do it, and stop dreaming about it too'. Perhaps it's still just too new-fangled an idea....but I don't think so. The systems on Steve Dashew's boats come to mind, though that is a whole different category of bucks. Think Dashew on a small scale .

Wil

Scott and Dave, yeh, 24v spares make perfect sense due to their (I'd guess) relative scarcity. Have you guys looked into the cost of things like 24v fridges or freezers? Is there such a thing as a 24v say RV fridge that would get you by budget-wise until you could buy proper, super-stud, marine 24v cooling units?

Rgds,
Wil

Scott, you have Wallas furnaces--niiice. I went to I think it was Scan Marine on Lake Union and looked at their Wallas furnaces and stoves. Nice quiet stuff, though the diesel stoves need more development. And the N47 is the boat I'd really like to have, though the KK42 I eventually find will do nicely.

Anyhow, how do you charge your large 24v house bank? 8x8D AGMs, you're pushing towards 2000A for a house bank and can just pour flat out amps into those suckers! How do you care and feed them?

I have run 12/24/36 volt boats and for boats under 65 feet or and see no real advantage to going to any one or the other system.

If the boat comes that way...great...but retrofitting one to a different voltage...you would have to know something I don't and having been a pro captain for a good number of years.

Worked in marine electronics as an installer for 5 years and currently work on many different size and voltage boats up to 65 feet...just don't see the advantage of switching....new build is one thing... but not retro.

psneeld, Ok, that's experience talking. And I am a newbie at this.

I want to increase my 12v house bank anyhow so that would be a sunk cost. If I plan them correctly, could I convert the same bank from 12v parallel to 24v series-parallel configuration? I can use the same wiring already present in the boat, it will unload it alot, maybe not such an advantage.

It seems to me that the major expense would be converting the various appliances (fridge, anchor winch, etc.) and charger (DC generator, large frame engine-mounted alternator). Some of these could be done piecemeal, if a hybrid 12/24v system is used during the conversion process.

The boat I'm looking at has a hydraulic thruster and I would want to convert the anchor winch to hydraulic since most of the plumbing already exists. The fridge they have now wastes too much space so I would want to change that anyhow.

It sounds like you think 24v vs. 12v is a good idea ("....new build is one thing... but not retro."). What in particular makes the retrofit not feasible in your opinion?

Ok, breaker panels just came to mind.....is that the big one, or is there other too.

Buying or replacing things that can run on the existing system that cost more or just don't need replacing unless the switch have kept me from switching.

Look...at some point arguing over a couple hundred, even thousand dollars to get things the way you want is peanuts in boat ownership...maybe I missed it...but what makes you think the "overall" system has to be switched. Many run a 24V thruster yet have a 12V boat...not a big deal...just not sure why you see this bg need to switch from the norm as has been said before...plenty of boaters have lived with 12V for a ong time with the same needs you have described....

If you want it...go for it...but I haven't ever seen the need to switch...but I would probably go 24V if a total rebuild. Why...why do I like bourbon over scotch???? Probably the same scientific reason for switching voltage...none....

I had my boat built with 24 V but not a simple task. We found several things that just don't come 24v and had to put in multiple 24-12 converters a PITA. Some advantages of 24v are in wire size and ability to send power further from source with less lost. Good for thrusters and starting motors. A mixed bag.

psneeld,
Fair enough. I advocate the same reasons that car manufacturers went to 12v from 6v systems, why some boat manufacturers build 24v systems in smaller boats. More efficiency, reliability, and power, less heat and voltage drops. I suggest that the 12v 'norm' will eventually go the same route 6v systems did, and for the same reasons.

What I trying to do is explore the possibilities. And advocating the 24v position. That doesn't mean I'll do it. I want to find out the specific pros and cons to each system. It sounds as if you like 24v, just don't want to make any redundant expenditures. Perhaps a 12v/24v system would alleviate those legitimate redundant expenditure issues, perhaps it's just too much bother to undertake. That might be where I come out on this too.

Appreciate the opinion and input, have a good day.

The fridge they have now wastes too much space so I would want to change that anyhow.

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How do you reach that conclusion?

caltexflanc said:

How do you reach that conclusion?

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The owner installed a separate icemaker (a good thing) but that left a large unused space right next to the fridge. I will look into finding a fridge that fills the space more and have an icemaker onboard as well. Don't know if there is such a thing. It's all theoretical anyhow, I don't own the boat yet.

eyschulman said:

We found several things that just don't come 24v and had to put in multiple 24-12 converters a PITA......A mixed bag.

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I can see how that would be a pita. Lack of 24v appliances and hardware will surely put a damper on 24v system evolution.

What were the things that didn't come in 24v form?

Not sure about the PNW, but out east here no issues sourcing 32 volt stuff, let alone 24.

Wil said:

psneeld,
Fair enough. I advocate the same reasons that car manufacturers went to 12v from 6v systems, why some boat manufacturers build 24v systems in smaller boats. More efficiency, reliability, and power, less heat and voltage drops. I suggest that the 12v 'norm' will eventually go the same route 6v systems did, and for the same reasons.

What I trying to do is explore the possibilities. And advocating the 24v position. That doesn't mean I'll do it. I want to find out the specific pros and cons to each system. It sounds as if you like 24v, just don't want to make any redundant expenditures. Perhaps a 12v/24v system would alleviate those legitimate redundant expenditure issues, perhaps it's just too much bother to undertake. That might be where I come out on this too.

Appreciate the opinion and input, have a good day.

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Please explain to me where a properly designed 12V system lacks any of these except needing heavier wiring????

Wil:

Ok, we can agree to disagree about 24v DC systems. But can you please drop the "hybrid" term. That term connotes two different power sources like a combustion engine and a battery/motor system. What you are talking about isn't.

David

I hear 3, maybe 4 questions being munged together, and it might help to separate them out. The original questions/suppositions that I hear are:

1) Is a 24VDC system better than a 12V system? The 24V system would of course have a 12V subsystem, but it would be primarily a 24V system. On bigger boats, say 50' and up, 24V systems seem pretty much the norm in modern builds, and it has all the advantages you mention. Yes, 24V is arguably better for a larger system.

2) Alternative DC charging systems. In particular, reducing or eliminating the AC generator, adding an engine-powered DC generator and bigger alternator(s) on the main engine, and adding solar and/or wind generation. All these have subtleties to them. I'm not at all convinced that an engine driven DC generator is better than an AC generator. The DC generator might be electrically more efficient, but teh AC generator is more flexible in its ability to power heavy loads like Air Con, washer drier, over, etc. Plus, you can charge batteries really fast with a big generator and enough charger capacity. And you need the chargers anyway (at least some of them) for charging on shore power. Personally, I'd stick with a reliable, servicable, AC generator. And keep in mind that fuel consumption for a generator is based on how much power it is generating, not how much it's capable of generating. It's just like your propulsion engines in that respect. So a smaller generator putting out 5KW and a large generator putting out 5KW will consume about the same amount of fuel.

Wind seems good, but personally I hate them. I've never had one myself, mostly because I can't stand them when they are 100 yds away on another boat, let alone on mine. They just make too much noise. And from people I've talked to who own them, they don't generate much power either.

I like solar, but there is a real question of whether you can fit enough on your boat to make a meaningful impact on your power budget. Unless it helps reduce generator run time in a meaningful way, it's just extra baggage. I'm struggling with this currently on my boat. The power I can get from solar on my boat is only a drop in the bucket compared to the power that other owners report using on a daily basis. But I'm pretty sure I can get my power useage down to a level where the solar will make a notable difference.

3) Converting a 12V boat to 24V. My guess it that it's not worth it. Yes, I prefer 24V boats, but the there is SO much stuff that would have to be converted. On your engine it's not just the starter, but the solenoid too. And the stop solenoid. And the alternator. And if there are any control relays or if it's an electronically controlled engine, you are probably out of luck completely. Same with a generator. Mine has a bunch of control relays. Plus you have all the control panels for the main and generator. Then there is the thruster, windlass, inverter, all your chargers, all your electronics (some can probably run on 24V, but don't count on it. Then lights. Nave lights, spreader lights, house lights, engine room lights, closet lights, etc. etc. And fans. Got blowers for ER ventilation, lazarrette venting, bathroom vents, etc. What about smoke detectors, CO detectors, automatic fire extinguisher systems. I think it's a very long list. If I were doing it, I would probably segregate the inverter bank and only convert that to 24V. But I'd think real hard about how big a difference it would make before going down that path.

psneeld said:

Please explain to me where a properly designed 12V system lacks any of these except needing heavier wiring????

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Ok, let me try to do that with specific examples. Inverters with 24v vs. 12v inputs run cooler & more efficiently, refrigeration compressors with 24v vs. 12v inputs run cooler and more efficiently, 24v anchor winches are more powerful than 12v winches with smaller wire runs. Using less current and more voltage is intrinsically more efficient and powerful. By its own definition, 24v is a more efficient and cooler-running system than 12v. Of course there's a limitation on how high one can go in DC voltage, but that isn't something I've researched. By the same logic, do you think a 6v system would be just as good as a 12v system? If not, that is exactly the same reason why I think 24v is better than 12v.

Here's a brief article by someone I greatly respect regarding electrical systems on boats--or entire very advanced long-range powerboats for that matter: SetSail» Blog Archive » Electrical Systems

djmarchand said:

Wil:

Ok, we can agree to disagree about 24v DC systems. But can you please drop the "hybrid" term. That term connotes two different power sources like a combustion engine and a battery/motor system. What you are talking about isn't.

David

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Makes sense. No more hybrid.

twistedtree,

Appreciate the reply. That's one long list of required conversions and is what I was wondering about. As mentioned in my opening post, I'm wondering just what is involved in the conversion, and whether technology has advanced enough that a retrofit is feasible and doable in a practical sense. Maybe it isn't. Per each of your points:

1) Agreed

2) The boat I'm looking at doesn't have AirCon, does have a clothes washer and fridge. Those would be the heaviest loads, though the washer is obviously very intermittent. Want to live on the boat in shorts and scandals anyhow. Is it possible to get away from battery chargers when on shore power--no, I'd guess running the little DC generator even if very quiet at the dock would quickly raise comments from the neighbors. But it wouldn't have to be a very big charger, as shore power can run inverter loads. Make the charger big enough to replentish power used by the 24v refrigeration system and maybe some more. You're right about fuel consumption vs. power output, I'd forgotten that. A given amount of fuel gives you so much power. So that leaves the underloading of the main propulsion engine (if it is the main source of battery replentishment) and perhaps even the generator, unless you've got some really big-ass 110v battery chargers (do they make 110v 300A battery chargers?).

I found a wind charger that I understand deals with what is both your (and my) objections, noise: superwind Gmbh . The output will never be enough for the typical wind conditions in a harbor, but I see it as only a device to stretch out the 'big-charging' intervals. Same with solar cells, though the technology has improved rapidly in the last few years. We hope to be on the hook alot on our eventual way to the Caribbean (my home stomping grounds) from PNW, so we plan on reducing our power footprint as much as possible commensurate with comfort. I think a smaller Krogen is amenable to that.

3) This is where the 12/24v system would be of real help. Don't convert any of the engine to 24v, leave it as-is. The 120hp Lehman is about as basic as it gets, like that. The DC generator would be one of the main expenditures. I see what you're saying: the breaker panels and the long list of all the 12v things I haven't thought of might be the biggest obstacle. That's one positive thing about a KK42; it's a pretty comfortable boat without getting into really complex and expensive systems. Of course, whittling away at the 24v system by what can be left as 12v eventually makes the whole exercise moot. That's why I started this thought experiment.

Thanks for the great input,
Wil

Also keep in mind that there is a limit to how much power you can draw off the belt and pulley system on the main engine. If you can find the detailed specs for your engine it will tell you. It sounds like you have a Lehman, so perhaps calling American Diesel will get you an answer. It's not just about the belt size and puttin on a bigger belt, but also about side loading of the pulley bearings for the idler pulleys, water pump, etc. I'd guess it's in the range of 10% of full power, so that's 12hp for your 120 lehman. 12 HP will generate about 8 KW max. But the real numbers may be less than that. I've got a 190A 24V alternator and an 85A 24V alternator on my 325HP Deere engine, and I understand that's the max you can do. That comes out to 6.6kw

twistedtree,

Yes, if this deal goes through, it's a Lehman. I've spoken with Bob Smith about it and had the honour and great fun of attending one of his 'Lehman University' courses. A couple of ways to deal with the bearing sideload issue is using twin belts or going with a serp belt. Bob has the pulleys for a twin belt install. But that's a reason why I'd like to go with a small diesel water-cooled DC generator--it provides redundancy, and with a medium sized, large frame, heavy duty alternator (say 150A) on the engine I'd be in decent shape. The little DC guy would be doing most of the work and enjoy the optimal loading of its engine.

Had a look at your blog and really enjoyed the Watermakers and Shore Power Conversion sections. I want to put a watermaker on 'my' boat and the Spectra is now on my short list.

Is your charging system set up so that both engine alternators can dump into your house bank?

What other house bank recharge system(s) do you have?

Do you carry alot of 24v spares?

If your refrigeration is 24v, is it hard to come by?

Are other 24v appliances you might have hard to come by?

Ok, that's a bunch of questions , but it's not just-kicking-the-tires questions.

My previous boat was principally 24v. My current one is all 12v. I say "all" because the 24v one had a transformer to convert to 12v for the stuff that only readily comes in 12v. I seem to remember buying 24v nav light and anchor light bulbs at a truck place, and waiting for a 24v shower sump to be got in specially.
My (admittedly limited) understanding of 24v advantage is, less voltage drop. There is a reason most boats run 12v, and why many run mains type power producing gensets. Setting out to use 24v seems to add an extra layer of difficulty choosing/procuring items. That said, it will be Wil`s boat, and Wil, it`s your choice, and exploring the issues is a good thing.

Wil said:

Ok, let me try to do that with specific examples. Inverters with 24v vs. 12v inputs run cooler & more efficiently, refrigeration compressors with 24v vs. 12v inputs run cooler and more efficiently, 24v anchor winches are more powerful than 12v winches with smaller wire runs. Using less current and more voltage is intrinsically more efficient and powerful. By its own definition, 24v is a more efficient and cooler-running system than 12v. Of course there's a limitation on how high one can go in DC voltage, but that isn't something I've researched.

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Just a couple of thoughts here. If the above, (highlighted), is true, why did the US persist with 120vAC for the domestic reticulation, when the rest of the world largely uses 240vAC..?

Also, why is 12v DC the norm for almost all non-AC purposes..? I suspect it is the ease of building 12v batteries, and the fact there are so many non-marine 12v appliances, (e.g. all/most recreational road vehicles), such that it is much more expensive to produce 24v appliances for relatively minor gains.

Finally, we, like you, wanted to avoid AC on the boat, so the only AC we use is for at-berth charging and to pre-heat the hot water before cast-off. The rest is off-engine charging, solar panels, and Airbreeze wind to augment that when the sun is down/obscured. We cook with propane, and have LED lights, and a small inverter for e.g., laptop charging. We are therefore very self-sufficient at anchor - virtually indefinitely.
It means we don't have aircon, and we don't run washing machines or dishwashers, but with only two of us, it works for us.

I certainly feel you could achieve all you want without the complication & cost of adding in the 24v side of things, but the DC diesel charger makes sense if you want to run much AC off an inverter. Solar and air power would struggle to cope with that.

Wil said:

Ok, let me try to do that with specific examples. Inverters with 24v vs. 12v inputs run cooler & more efficiently, refrigeration compressors with 24v vs. 12v inputs run cooler and more efficiently, 24v anchor winches are more powerful than 12v winches with smaller wire runs. Using less current and more voltage is intrinsically more efficient and powerful. By its own definition, 24v is a more efficient and cooler-running system than 12v. Of course there's a limitation on how high one can go in DC voltage, but that isn't something I've researched. By the same logic, do you think a 6v system would be just as good as a 12v system? If not, that is exactly the same reason why I think 24v is better than 12v.

Here's a brief article by someone I greatly respect regarding electrical systems on boats--or entire very advanced long-range powerboats for that matter: SetSail» Blog Archive » Electrical Systems

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yes..yes...I think most here understand basic electricity...

I would think that if there was that much to gain by switching....12V systems would be a thing of the past.

The ACTUAL gains may be insignificant if 12V systems are wired correctly or slightly oversized. Based on wiring charts I use...there's a lot of latitude.

I'd love to see some actual "cooler running" numbers for the average boat.

Work is still work... and if you efficiently transmit 12V or 24V....and the losses are minimalized....woopie compared to the redoing, searching for and stocking everything to 24V.

Again...new boat - maybe 24V...old boat...12V it would stay.