In Part 1 we learned that it was inefficient, and often impossible, as well as potentially dangerous, to supply the high-load equipment, that so many cruisers seem to want, with a 12-volt system, regardless of the size of the battery bank, since the cabling and fuses simply won't support it.
And, further, that the solution to this problem is either to forgo all very high-current (amperage) gear, or select a boat with a 24-volt system—there are no other good options.
So let's look at that:
Hi John
I decided to forgo the 24 volt system and stick with the 12v system for reasons you described . Our systems are complicated enough without having to worry about converters . I agree 12v boats are just fine,when done correctly.You must use proper sized wire for each application and current draw and the best lugs properly crimped and heat shrunk to the ends of the cables . Large buss bars that can handle all the current and more. I also use a contact past that insures good contact between the lug and buss bar. Yes the cabling is expensive , I actually just spent 900$ on wire yesterday for our new hydraulic system (winches, back stay, and boomvang) . Im a tinker nut and love to maintain things on a boat gives me something to do when not under sail. Im always excited when something breaks .
Regards John.
Hi John,
I would suggest not using powered hydraulics for vang and backstays. Use a hand pump so as not to lose touch with what’s going on and break something: https://www.morganscloud.com/2020/11/16/rigid-vangs/
Hi John
Yes I thought of that as I was designing the system . The vang and back stay are rated at 5000 psi , my on board system is limited to 3000 psi max , I have also have installed pressure gauges and adjustable pressure regulators, also throttles on each of the cylinder circuits . I will set them up so even if somebody leans on the switches the pressure will not be able to rise high enough to damage anything .
Thanks for the advice .
Regards John
Hi John,
Each to their own, but, even though we too have a pressure relief, I still like the tactile feedback of the handle getting harder to operate as the load increases. That way if the load increases when it logically should not, say if something is fouled on the main, we will notice. In this kind of case something can get damaged long before a 3000 psi overload trips.
For example, a friend of mine, who is a fine and experience seaman, tore the end off his spinnaker pole last summer with a hydraulic sheet winch when something fouled to pole.
I write the above, not to be argumentative, since clearly you are happy with your solution, but to make sure others understand that an overload cut out does not necessarily protect from damage.
“12 Volts is still fine, and its very limitations protect us from our own destructive lust for complexity.” That’s the kicker, isn’t it? Accepting some limitations on complexity and often illusory convenience and acknowledging that living on a boat is not like living on land…nor should it be…actually creates freedom: freedom from worrying if your gadgets are going to cannibalize time better spent sailing. A commentor in the preceding part 1 mentioned about the parasitic draw of inverters being 3 amps…we just don’t run the inverter to power things like the clock on the microwave and are pretty parsimonious with it, period. It is easier to change attitudes toward creature comforts than cabling and batteries, I think. That way, if we have to run the inverter (and that has been necessary a few times at sea), we have the reserves to do that.
This will no doubt change in the future, just as boats went from 32 VDC to 12, but simplicity will, I hope, never lose its appeal on boats.
Hi Mrac
Just a comment on the parasitic current draw on inverters. Ours when on will draw 7 amps on invert mode other wise when in the search mode looking for someting to turn it on, it draws .2 of an amp . We have a 110 volt headhunter mach5 domestic fresh water pump with its own electronics on board to monitor itself. That was enough draw to turn on the inverter to invert mode there by using 7/12v amps to just to sit there and idle. The solution was to bypas the headhunter control circuit by using a basic domestic pressure switch to turn the pump on and off . Works great for many years now and leaves the inverter in search mode.
Regards John.
Thank you for the clarification. Our situation is comparatively simpler: we just have the inverter on selectively and tend not to leave it on. We also use quite small auto-style inverters in DC sockets for low amp draws, such as charging phones, as opposed to switching over the Victron. Perhaps it’s a hangover from tent camping, where 4 AA batteries in a Grundig radio or an LED light seemed like luxury!
My neighbour has gutted his 70ft yacht and is rebuilding it at 220 volt AC (shore power in the Netherlands). Will use convertors to 12v DC where needed. Figures he’ll only need a few convertors, probably right next to the 12v appliance. Figures he’ll save a ton on wiring and make pumps, lighting, fridge etc a lot cheaper too. What do you think of going that way? After all, if you go that way there is not that much that requires 12v.
Hi Rob,
I guess that begs the question: where is he getting the 220 volts when not on shore power? If batteries and inverters, that means his system is not really 220 volt. If a generator, that’s an environmental disaster as I explain here: https://www.morganscloud.com/2020/11/03/efficient-generator-based-electrical-systems-for-yachts/
The other aspect is that many household appliances are horribly inefficient, particularly refrigeration.
In short, such a system would not be my way.
We have pretty much gone down this path ourselves. Once you live with it, if your boat is big enough, (45 feet in our case, and otherwise running 24 volts) it’s a no-brainer. Especially with the increasing availability of bio-diesel: zero net CO2 emissions. Too many yachting products are really only made for the weekend market. And applying the minimalist cruising sensibilities of our youth on passage means we can cruise independently for ages. But I would like to hear what you mean, John, when you say that domestic fridges are horribly inefficient (below). We have found the cheap domestic fridge to be infinitely more satisfactory than it’s marine equivalent. Have you got an article on that?
Hi Mark,
Generally domestic fridge have much less insulation than a good custom built box like ours (less than half) and also they are air cooled, rather than water cooled, which is far more efficient.
I don’t think the “domestic 120V / 220V fridges are inefficient” argument is all that strong anymore, with Energy Star etc. mandates having greatly improved their performance. A modern 20 cubic foot domestic fridge uses about 1.0 to 1.3 kWh/day. Boat fridges that do better than that mostly do so by being much smaller and by having top-loading instead of front-loading doors. If you compare “like for like”, though, 20 cu.ft. of front-accessible custom boat fridge with standard marine compressors is unlikely to come in much better than 1.0 kWh/day no matter how well you build it.
The downside is that you’re introducing a device that isn’t really meant to move while in use (how many domestic fridge shelves rely 100% on gravity to stay in place?) and is impossible to fit into oddly shaped spaces, plus you’re discharging waste heat into the cabin air, which is non-ideal below latitude 40° or so.
Hi Matt,
All good points, although surely water cooled is still an advantage? Anyway, as you say, the thought of a household fridge on a boat offshore in big breeze and swell is sobering indeed.
Not when you look at total wh / day vs volume.
Running pumps costs power and leaks 🙁
Modern refrigeration is efficient.
Door opening is an ongoing debate. (Not as simple as it appears)
There’s no doubt that the inbuilt purpose built fridge is the best….. until it needs repairing. My feeling with anything on board is that it has to be repairable at sea, or easily replaced, or easily done without, to be considered worthy. It’s sounding like we need an article about boat refrigeration please.
Hi Mark,
I will keep it in mind. Just finishing up cooking options.
I absolutely hear you on the complexity front; it’s way too easy to go overboard on this kind of conversion and finish up adding problems.
My broad layout goes like this; 24v DC House lithium bank with all major charging sources and load busses kept separate. All mechanical loads, autopilot drive, pumps and winches are at 24vDC, while all other instrument and lighting loads remained at 12v DC as per the original boat via DC converters.
DC to DC converters are cheap as chips; I’ve got five of them, four installed and one spare. I carry spare 24v DC pumps for the bilge, fuel and fresh water pumps. The rest are non-critical. I had to replace all the old pumps and autopilot drive anyway, and the only item that hurt a bit was a new 24v anchor winch motor.
The engine starter and instruments remain a separate 12v subsystem. Lead acid batteries are perfectly fine for engine starting and have to be a cranking type anyhow. It’s charging needs are minimal and I’ve simply put a 16A mains charger and a 50W solar panel dedicated to keeping it pumped up. (This mains charger is actually connected to the inverter supplied 240v which is in turn powered from the 24v House bank or from shore power. This is a little bit inefficient, but the load is so small it doesn’t matter much.)
The large 180A 24v engine mounted alternator goes directly to the House bank and has no direct connection to the engine 12v battery. No ’emergency paralleling’ or attempt at using the alternator to do two different jobs at once with VSR’s or the like.
This means I have in essence four electrical subsystems, 24v DC House for energy storage and all larger mechanical loads, and then powered from this a 12v DC lighting and instrument system, plus a simple 240v AC inverter system; and then finally a highly segregated 12v DC engine system. Each one has it’s own switch panel. I put a fair bit of effort into ensuring it’s really obvious which is which when looking at it with good labels, colour coding and separate ducting where possible. (Over time I suspect I’ll gradually cull the loads off the 12v side and end up with just the N2K busses.)
I agree that a conversion like this does have it’s costs and pitfalls, but a simple and logical segregation like this does help a lot. Overall I’m very pleased with the result I got to.
That does make sense in principle, and it’s pretty easy to do. I’m assuming that if you do manage to run the engine start battery flat (which should only happen very rarely), then you’d do a physical swap out with the proposed buffer battery.
My counter is that you might be better off just replacing the engine start battery every 2 -3 years to ensure it’s always in good condition. And if the engine doesn’t catch within the usual few seconds, fix the problem rather than just cranking and hoping.
And DC-DC converters are very cheap, just keep a spare or two on hand, and its the work of moments to swap one out. Also you might want to keep in mind that if a DC converter does fail, yes the battery will keep things running but unless you specifically monitor and alarm for this scenario, you might not notice until it goes flat anyway. (Plus my boat is a relatively low volume 40 footer and this extra buffer battery wouldn’t really have an obvious, otherwise unused place to go.)
John’s instinct for simplicity is almost always right, it’s far too easy to add stuff with very good intentions that really doesn’t wind up adding a lot of value. On the other hand I don’t see a lot of downside if it’s something you really want to do.
Hi Philip and Mal,
I do have a gang solenoid to cross connect house and engine if the engine battery dies, but in 30 years I have never used it. The ultimate simple solution on a singe voltage boat is a set of jumper leads! Can even work on a 24/12 boat, by just jumping half the 24 volt bank to the starter. Caution: that last is only a good idea for those that clearly know what they are doing.
Hi Philip,
Sounds like it works for you, and that’s ultimately what matters. That said, I personally would classify your system as highly complex. Just shows that simplicity is in eye of the beholder. I guess the key thing is for each of us to stick within a level of complexity that we have the skills to manage. What really scares me is when I see people with very few electrical skills taking on systems like yours, just because they have read somewhere that this is the “best” way.
Also each of us must access our willingness to take on complexity. For example, I have the skills to maintain your system, but I’m just happier with a simpler system.
Simplicity is definitely in the eye of the beholder, yes. That said, when I started sketching out what Philip described, it looks an awful lot like one of my favourite electrical architectures, the one I often go to as the best all-around choice for a new or total-refit 15 to 40 ton liveaboard cruiser when the engine of choice isn’t available in native 24 V. The only major differences are that I usually recommend charging the starter battery from a dedicated 24-to-12 V charger, rather than via the AC bus. And I don’t usually recommend lithium unless the owner is really keen on it and understands the trade-offs versus AGM, flooded, or carbon foam Pb/H2SO4.
It sounds complex written out in words, but drawn out on paper it is an extremely easy architecture to trace, troubleshoot, isolate defective items from, and add to at a later date. The complexity I see there is entirely in the choice of lithium batteries with their associated BMS and control requirements.
Hi Matt,
I would agree with that, it’s lithium that puts it in the realm of “too complicated” for me. That said, we do also need to keep in mind sourcing problems in remote places, which has always been a big driver of my system decisions. Try finding a 24-12 volt power supply in Greenland or even the Bahamas. A fully 12 volt system can be fixed just about anywhere.
Having just gone through the electric design for our boat, I didn’t find the 24/12 V system more complicated. Our approach is similar to Philip’s. Winches, bow thruster, windlass, inverters and house power generation is actually less complicated and costly due to the smaller wire sizes and some parts. Except for a few 24/12 converters, it is exactly the same number of wires and parts. The key is using LiFePo house batteries, building in redundancies and carrying a reasonable spare inventory.
Hi George,
I really can’t see how using LiFePo batteries makes 24 volts easier. Batteries, regardless of chemistry just store electricity, they don’t change the fundamentals of voltage, amps and watts, which are what matter when making the 24 or 12 volt decision.
You need 8 cells for 24V, running on 1 Battery Management System (BMS). The resulting batteries are comparably small and don’t need to be vented, like lead batteries. 200 Ah are about 60 kg for 24 V, and that amounts to something around 5kWh.
There is no real penalty, whether weight or cost going with 24.
Hi George,
That’s true, but it’s also as well to be aware that a system configured that way will not be at all fault tolerant since the failure of a single cell will bring the whole thing down with no way to fix it until you can get a replacement cell, which might be quite hard to do quickly: https://www.morganscloud.com/2017/01/28/three-tips-to-make-your-cruising-boat-more-reliable/
Also the whole issue of venting and containment is more complex than that with new regulations standards coming that will make boats with systems that don’t comply impossible to insure.
Re. 48 volts.
The car industry is starting to push quite heavily towards 48 V for mid-range to premium cars that are not battery-electric. The IT industry has been there for years, with 48 V PoE up to 70 watts being a widespread standard. It’s a really good choice of voltage; high enough to move 7 or even 10 kW efficiently while still being low enough to not be an electrocution risk. Things that need awkward 1 AWG cable in 12 V often get by just fine with 6 or 8 AWG at 48 V. The carmakers are also pushing to replace engine-driven air conditioning compressors with standalone 48 V electric ones, which will give marine equipment makers an easy off-the-shelf option for fridges & freezers.
I strongly suspect that Integrel is, beneath the branding, largely based on standard 48 V components from the automotive tier-1 suppliers.
I expect it will be 6 to 8 years before we see enough 48 V hardware trickle down to the marine market for it to be an obviously viable option for most of us. Mixing 12, 24, and 48 V in one system seems dumb. You’d want to go all 48 V except for the occasional 12 V device powered via a DC-DC converter. So this kind of system isn’t going to be common until you can get a wide variety of thrusters, windlasses, power winches, fridge compressors, etc. as well as engine starters wired for native 48 V.
Hi Matt,
Good to hear that cars are going away from the engine driven compressors that eventually made their way, sadly, to boats. Even at 12 volts its better to drive the compressor with an electric motor as we have done for 26 years and with 24 or 48 it’s a no brainer.
And I agree, eventually we will see 48 volts.
One thought is I believe I’m right in saying that 48 volts takes special switches and breakers because of the problem of ark welding the contacts? If so, that could be a real gotcha for those converting and thinking that they can use existing breakers because they are marked with higher voltages, but missing that said rating is for AC, not DC. Have you heard anything about that?
Yes, most switches & breakers meant for 12/24 V DC or 120/240 V AC are not ok at 48 V DC.
The problem is switching speed. On AC, the current will always zero itself within 1/100 or 1/120 second, extinguishing any arc at the switch. On DC, an arc across a just-opened switch can persist, particularly if it’s an inductive load like a motor. That erodes the terminals and leads to early failure of the switch. Thus, DC switches & breakers must have a very fast spring-loaded action to break any arc. At 12 V, the same spring as used in an AC switch is usually sufficient, but at 48 V you need something faster.
I’m sure the likes of Blue Sea Systems will release 48 V breakers when the time comes, but I also suspect that the majority of 48 V boats will use distributed power with few or no mechanical switches.
Hi Matt,
I figured as much based on theory, after comment brought it up a few months ago, but thanks for confirming it.
Sadly I’m guessing this will be an unintended consequence for yachties that go 48 volts since I have not seen it mentioned anywhere else.
This wouldn’t be the first example I can recall of the depth of AAC discussions revealing either shortcomings or fatal flaws of new technological directions in marine hardware.
Well, I checked the Blue Sea Systems “A-series” breakers we’re currently installing in Maverick V, and it turns out they’re already rated for 65 V DC / 250 V AC. So that particular problem is already solved, at least from the biggest vendor in the segment.
Hi Matt,
Good to hear. That said I’m pretty sure the older breakers on most boats will be a problem. Not a big deal for those that know, but just another gotcha to get the unwary.
Matt,
If you want a very well rated and exceedingly reliable switching contactor, take a look at these Gigavac devices:
https://www.gigavac.com/sites/default/files/catalog/spec_sheet/gx14.pdf
The contacts are sealed in a small vacuum chamber with flexible metal bellows. Because there is no gas to ionise the contacts only need to move a tiny amount, and there is never any arcing. They have exceptionally good switched current ratings for their size and cost.
Combine this an inherent isolation from salt laden air and you have a great device for marine applications. A latching version is also available.
I used to sell something similar for industrial applications (typically MV rated) and the clients who were willing to pay the extra were always very happy with the value they delivered.
Hi Mal,
That’s pretty much what I did to come to the same conclusion.
Re. 24 volts.
Another significant advantage of this class of system is that 24 V is a near-universal standard voltage for industrial controls. Choosing 24 V may rule out the use of much retail / consumer grade RV & marine gear that wants 12 V. But it opens up much of the catalog of industrial automation vendors like AutomationDirect. That’s a market that has near-zero tolerance for unreliable crap and unhelpful tech support (downtime on a production line might be worth $10,000 or even $100,000 an hour) and also has very little tolerance for poor documentation and opaquely marked-up pricing. Once you get beyond “normal yacht” and into “big yacht with 7 / 8 figure price tag” territory, you find this kind of gear *everywhere*, but it’s actually rather affordable compared to what you’ll find at the local marine supply shop.
You’ll also find 24 V gear in easy supply for large buses and trucks, along with mechanics / technicians who are used to working on it.
And, as John has said, a 24 V boat naturally wants DC-DC converters for the 12 V gear – either a small one powering each device directly, or a larger one for 24V-12V charging of a very small buffer battery. You may think that a 12 V main bus is always 12 V, but it’s not; the transient spikes from a motor suddenly stopping can be on the order of 100 V for extremely brief periods, and the available voltage can drop to 6 – 8 V during engine cranking. Isolating your electronics from that is highly desirable, and relatively inexpensive.
Matt
And as a retired industrial automation engineer I have to admit this had an impact on my choice to go 24v. It means that if I really go mad in my dotage I can add PLC’s, sensors and all manner of hardware that I understand and believe in with very little difficulty.
I realise a multi-voltage system like I’ve described above does run against the simplicity mantra, but with logical and physical segregation this risk can be substantially mitigated
Just think of it as a tree, with the 24 House bank being at the base of the trunk. It’s charged in one direction by the roots, and the loads spread upward via the trunk and branches to all the individual electrical loads. At each junction there is a fuse. The key feature is that no branch ever loops back to the trunk or another branch, which enforces functional segregation.
Everyone understands how a tree is laid out which makes visualising the system predictable. That and a simple single line diagram attached to the inside of the main electrical cabinet door should be enough to help most people work their way through it.
Hi Philip,
What a great way to explain it. Love the tree analogy.
John, this is quite a discussion. I thought I was well up on my DC knowledge but find I learn something new with each post. (ie, NEMA 2000 busses only 12v.) My Nordhavn’s electrics are quite overbuilt as you know. I find it a challenge to improve upon the systems. I have made several tweaks that I shared with Nordhavn and will here once you get more information out. I too like the Victron chargers and share this good recent experience. Victron replaced free of charge my 6 year old 100A/24v battery charger after I returned it for repair. It was still working but something was amiss with the sense circuit. It wouldn’t charge more than 30amps regardless of the battery state. No questions asked! Not even a freight charge.
Hi Bob,
Great to hear that story on the Victrons since my experience with them is second hand (other than battery monitors), albeit good second hand based on Steve Dashew’s experience.
I have found that a good source of 24V equipment can be from truck suppliers. Truck systems (in the EU, UK) commonly have 24V for the large engine starter motor and as such a lot of cab ancillary equipment is also 24V. My last purchase, 24V LEDs for backlighting galley cupboards were 24V articulated trailer side lights. In addition some domestic items, such as 24V truck cab fridge freezers and micro waves are easily available, although choice is limited and quality would need to be considered for a marine environment.
Hi John,
I especially like your section on 12V still being fine. If I were to rewire our boat today, it would stay a 12V boat and I would put up with the additional weight and struggle of larger wire. If we went more gear heavy, then I would be inclined to go 24V. For those of us with smaller engines, one annoyance is that you get stuck with a bigger start bank than is otherwise strictly required just to get your voltage and I really don’t like splitting voltages (the NMEA 2000 problem is a really annoying one).
I have actually sailed rather large boats that are still 12V as they have been kept simple and high loads go hydraulic. These boats might have 100+ cabin lights but with LED, this is just not that high current, the issue is stuff that you have highlighted like cooking. I have noticed that more items like windlasses on big yachts are going AC but I would not do that until you are at a size that you are committed to having AC at all times anyways and even then you should analyze for peaking (I know of 1 where they can’t break out the anchor unless they shut off the rest of the loads, scary). I have mentioned elsewhere that I have seen a shift away from hydraulic towards electric for increased efficiency but that really only applies for things that are used continuously, something like a windlass or the actuators on a fishing boat don’t actually use that much energy, just peaks at high power. Hydraulics are hard to beat when you need a whole bunch of actuators that will all be intermittent so that is why with electrification we are seeing things like dozer drives rather than blade functions. The one thing that you do need to watch is that you can clutch out the hydraulic pump when nothing will be required for a while.
I also agree on 48V, at this point in time it is simply not a practical house bank voltage, maybe in 10 years it would be worth another look, especially if we are moving on from lead acid batteries.
Eric
Hi Eric,
I had not thought of the peak load filter for deciding whether or not hydraulics were the way to go. Academic for me, in that I would never want a boat that complex, but still a great way to think about it that explains why fishing boats tend to use hydraulics for those functions. Thanks.
Talking of scary, on the superyacht I did the guide job to Greenland on we had to start the main engine to hoist or reef the mainsail since only the PTO was powerful enough for that function. Ditto the thrusters. (The winches could be run from a 24 volt driven hydraulic pump in the engine room.)
Wait, it gets even more scary: the boat had to have a special slipping transmission, like sports fisherman use to go slow enough in idle to dock or trawl, so that the revs could be high enough on the main so it did not stall when the bow thruster was used. Without that transmission we would be approaching the dock at 8 knots to keep the revs high enough for the PTO.
Hi John,
Scary indeed. My observation is that many of the yachts are riddled with single fault systems that are very hard to work around. Cruising boats are often small enough that a little inventiveness, some line and maybe some blocks can get you out of an enormous range of issues but the loads on those boats are simply too high to always be able to do that. My experience is more slanted towards the tall ships community rather than yachts and these vessels tend to have plenty of crew and systems originally developed in the pre mechanical actuator days so even though they might be converted to hydraulic or electric, there is still usually a manual workaround. Whenever I think about what is needed for systems, I think of boats like the fishing schooners where the only winch aboard would be the manual anchor windlass and everything else would be manual for boats displacing upwards of 300 tons sometimes (yes the windjammers were far more extreme but square riggers are just a different ballgame).
Yachts do tend to be powered so that they can motor at kind of ridiculous proportions of theoretical hull speed. Maybe they should all take a class from some of the old tug masters who drove the direct reversing boats, to me those were the coolest although somewhat tricky.
Eric
John-
Great article, I often wish my boat was 24 volt for all the reasons you site but the complexities of changing it over make my head hurt (and I have degrees in electrical engineering).
I was surprised to read you are using an electric (induction) cook top. There must be something monumentally wrong with propane to take perfectly good battery amp-hours and deliberately turn them into heat (and nothing else). We have a Force 10 stove and oven that while not perfect work pretty well (would love to have GN Espace if they were sold in the US).
I’d still struggle using a gen set to create heat in a galley when the same is available from propane and is so low tech. Am I missing something?
Ron Kraus
Annapolis, MD
48′ Custom Bruce Marek
Hi Ronald,
Not sure where you got the idea we were using induction. I experimented with induction with an induction ring but we are a propane boat. More coming.
Crikey! A toaster draws as much as your windless! Fire really was a wonderful invention. When it comes to cooking I will continue to use fire, and leave electricity for other jobs.
Hi PD,
A lot of wisdom in that thought!
It’s easy to not realize just how much energy it really takes to make heat, until you try to do it with electricity. (Pro tip: never leave an electric heater, hot tub, etc. turned on when you don’t actually need it. 5 kW * 24 h/day * 50% duty cycle will make the power company’s financial manger drool like a dog.)
We cook mainly with propane on the boat, too – but I do pull out a portable 1-ring induction unit when on shorepower. The improved safety with kids on board, plus shorepower being included in the slip fees vs. schlepping propane tanks in the car to be filled by some sketchy dude surrounded by cigarette butts and rusty chain-link fence, make a compelling case there.
Last August in Scotland you couldn’t get propane refills at all. It was blamed on Brexit …
The electric kettle got us through in the anchorage and we ended up taking a jet boil for underway. Rather dangerous, really.
Propane works well in the camper that I used to have in the US, where it can be topped of in many gas stations, but I loathe the nonsense with bottles, adapters and the like.
The very definition of seamanlike prudence.
Toaster 800 W
windlass 2300 W
while an induction top is rated at about 3000 W (2 burners), those cycle on and off, so one burner with something simmering being on 1/3 of the time takes about 500 Wh.
A pain on lead batteries, but no big deal for a LiFePo of a reasonable size.
My compromise in build / conversion is
220 where possible
12 for traditional loads
48 for storage / inverter / solar
Local AGM 12v on float beside each high current load with local 48-12 dc dc converter
This allows flexibility in emergencies, isolates faults, keeps cable sizes low and voltages reasonable.
Keep a spares on board (chinese) for emergencies
Designed my system for a 50ft ocean cruiser around 24v……found all major components aside from Nav electronics & radios available in 24v…even then over 1/2 nav gear is 24v.
Use a 24-12 converter to feed 12v bus, with cross over switch for emergency back up from 12v starter battery (engine & genset are both 12v :)…..which also works to back up the starter circuit.
Used SSB extensively on passage, to provide linkage to nets/boat buddies. Steel hull, so we are boomers transmitting, but found the Victron 24-12v converter noisy…had to turn it off to hear weak signals (and there was always a weak sister out there). Tried various filters, ended up installing a 12v buffer battery, and turning off 24v system when required, but it was a pain, as we lost the autopilot drive.
Unfortunately my 24-12 converter & SSB radio were too close together, and by the time we figured it out, there was no room to move……and driving SSB radios is in the converter specs.
so watch for radio interference when you select your converter/inverters!
Hi Norman,
Good tip, thanks.
If you’ve already gone over all the possible grounding issues with a fine-tooth comb, have clipped ferrite chokes all over the place, and are still picking up power supply noise on a radio that draws less than 15 amps, I might suggest trying a Murata BNX filter in the DC power feed to the radio. Some soldering is required, unfortunately – I don’t think they are available with screw terminals – but they are very effective, knocking 40 to 70 dB off anything in the 1 Mhz to 1000 MHz band that tries to get into or out of the radio via the DC wires. And they’re only about $15.
Slipping a $4 ferrite choke over the wires to both input & output sides of a DC-DC converter, as close as possible to the terminals, should be standard practice. These converters do produce a lot of RF harmonics that may not be fully damped out.
Great advise, thanks
Too late, now, but there are 24 V SSBs
https://www.svb24.com/en/icom-marine-ssb-hf-transceiver-ic-m804-eu-approval-24v.html
As ever, a very useful article.
We are fitting a 48v system on Black Sheep, though the only things that will run off this will be the electric motor and the inverter. The diesel is long gone. The rest of the boat will be on 12v for convenience with a small lithium battery bank as well as a 48v to 12v converter, so that if the main (propulsion and luxuries) bank goes down all essential systems will still function. Cooking is done on good old paraffin, so it’s especially handy to have an electric kettle available when you can’t be bothered with the priming.
Hi Tim,
I think it makes a lot of sense to use oil based fuels for cooking on an electric drive boat. Counter intuitive, but true, as Jimmy Cornell just found out the hard way. Thinking about an article on the usage profiles that can make electric drive work.
More on liquid fuels coming next.