Antrepat

Well, fortunately that particular one would not be one of my risks, since I'm not trying to connect the engine to the prop at all... After more homework I've come back to the issue that the most challenging component is the BMS. There are loads of dodgy cheap ones around but finding one that terminates charge based on residual current as well as voltage, and can send an external "enable/disable charge" signal, and works for 16s, is proving very difficult. The REC Q seems to judge charge termination based on voltage and coulomb counting. Off-topic, however. I'd better review some of the BMS threads on here...

I'm not belittling the complexity. I'm not expecting to buy a bunch of stuff and connect all together with wires and prayers and have it just work. I know sophisticated devices like BMSs and motor controllers will have to be configured according to a well-planned, well-informed scheme. I know, and I hoped this at least was evident, that LFPs have very particular management and charging requirements. I know a generator set is not really just an alternator bolted to an engine with a start button. I know I'll need all manner of sundries like contactors, control interface devices, hardware, fusing, junction boxes, bus bars, and terminals. I'm prepared for it to take a long time and a lot of careful research and planning and acquisition of new knowledge and skills, but this isn't my first rodeo - I've been writing computer software, building databases, analysing data, and engaging with all manner of practical technical matters for 49 years, and I am capable of doing the homework, designing at a system and a component level, formulating and evaluating options, considering multiple factors, resolving conflicting requirements and, above all, having the patience to wait until I am properly prepared before proceeding. I humbly want to give it a go, I will graciously accept any advice offered, and like I said before, if it's not feasible, I will accept that, but please don't think I am going blundering into this like a damned fool who has more money than sense. If that's the impression you've got of me then I've communicated badly about my attitude and intentions.

My battery will be LFPs. Unless I'm mistaken, these chargers are all for LA traction batteries. They will not operate at the right voltages, nor will they terminate charge based on a precise voltage/current combination threshold, nor will they probably take an external control signal to shut off if the BMS alarms and disconnects the LFPs.

If you don't mean something like this monster, could you perhaps drop a link to the one you mean?

Yep. More expense for the AC+separate transformation/rectification solution, then. I researched this further to illustrate that this is a more expensive solution. I'm not going round in circles. I'm clear what I think is the right solution, and it's the one you seemed to recommend too: using an OTS genset like the Beta 6/2 as an indicative template but substituting a different axial alternator to avoid all the issues with transformation and rectification of AC or Heath Robinson belt and bracket arrangements. The Sincro alternator and indeed the engine with the right start/stop controller will respond to a start/stop signal from a BMS that can generate it, like the REC ones can. It also has (even if the exact details of the electrics need clarifying) a voltage and a current control function, if just start/stop isn't graceful enough. Unless there is some kind of high-falutin' wizardry about that genset that means it has some complicated and expensive other element beyond an engine, an alternator and engine control, I fail to see where the massive hidden cost is beyond the cost of one of those engines (£2k + VAT), the cost of the alternator (£850), and the cost of the engine control equipment (£don't know but I'll find out). Unless that alternator is unreliable or the rig doesn't fit in the space available, what am I missing?

I have just found this, however: https://www.meanwell.eu/webapp/product/search.aspx?prod=RST-10000 ...with remote on/off, which means the REC Q BMS can signal it to terminate when a predetermined SOC is achieved... ...but it's £3k+ so that's the cost of the AC generator plus the cost of this to rectify and transform... So is that better than taking the components of a tried and tested marine generator, and substituting a different alternator that delivers the actual voltage DC needed, keeping everything else the same (and choosing the uprated version to compensate for lower efficiency of lower-voltage alternators)?

Not sure where the skin tank is in this picture. I have one already but I'm guessing the motor cooling and the engine cooling can't be intermingled... The exit from my mooring is directly onto the Calder. The Calder & Hebble Navigation has stretches of the Calder. Then there's the Aire, the Ouse (tidal to Naburn)...I'm not planning to navigate against any tidal flows but I do need the power for manoeuvre on rivers.

Perhaps I've looked in the wrong places, but I haven't seen any 230v AC - 48v DC chargers that can deliver 0.3C for a 400Ah battery. The biggest Victron is the 50A Skylla TG at £1,800, so I'd need three of those in parallel: £5,400. I know Victron kit is gold-plated but buy cheap, buy twice. A forklift charger will be brilliant for lead-acid traction batteries, but would only be suitable for LFP if it could be calibrated to supply the right voltage accurately (say, 58.0v) and to be shut off promptly upon a signal from the BMS. I did look into these the last time I was considering all this, about 18 months ago, but the ones I saw didn't look very adaptable for the different chemistry. I suppose "shut off" could be achieved by simply operating a high-power relay on the input, but the AC supply would need to stop at the same time or there'd be nowhere for the power to go - I'm guessing running a 7kW generator with no load attached would cause problems (explosions, fires, suchlike). I'll look into it again to remind myself why I gave up on that idea in the first place (though I suspect it was more to do with the outrageous price of an off-the-shelf marine generator ).

Yep, I know. Just as well I like a challenge, eh? Look, if it turns out not to be feasible or affordable, that'll be disappointing but I'll just have to accept it. I enjoy the process of evaluation in itself and I hope I always welcome straight "that isn't realistic, think again" talkings-to (@Tony Brooks). I'm aware that there is a risk of thinking something looks simple and cheap but the detail will reveal why it's not, so it's that detail I'm working on assembling. I thought that too, having reviewed the full range. Any comment on water-cooled vs. air-cooled, especially as continuous running would be at a power much less than the "continuous running" rating? Voltsport say "To run at or beyond the continuous figures, a decent cooling system is needed", but "Continuous running: 1210RPM, 90Nm, 12.4kW / 15.3HP to the propeller", which is vastly more than the 3 or 4kW I'd typically be doing to potter along at 3mph. (EDIT: but that is a 205W_08016 motor.) Mountings: Voltsport's Direct Drive Kit appears to come with a mounting frame. I wasn't proposing to just buy a motor and take it from there, obviously. Good. Do you mean boat speed or rpm? Attached graph from the 205W_12013 data sheet suggests 3kW at 250rpm, 7kW at 500rpm, 14kW (surely peak for our needs) at 1000rpm, which I thought fitted in with the advice about power within a <1000rpm spin speed range with a suitable propeller. Incidentally, what values did you use when you ran that propeller calculator?

Wise words. I have no intention of spending any money at all until I am absolutely clear what I need to achieve and exactly how the equipment I select is going to integrate to achieve it. The different functional components each have to be fit for purpose, safe in operation, to fail-safe, and to be reliable and affordable. Here's a starter list of elements. Battery structural design and location Battery management, monitoring and protection Charge supply Charge initiation, management and termination Power output control Propulsion System-level electrical safety protection

Not horizontally, certainly, but on a different orientation, possibly. It'd be a very tight squeeze on the left, no matter what orientation. None of the combinations feel comfortable. I do want to be realistic, I assure you, and I appreciate your honest opinion. If the belt-driven alternator conversion idea is not realistic, I'm very happy to be told straight that's the case. I always preferred this solution anyway, but I thought it would necessarily be much more expensive. I never fancied Heath Robinson belt-drive arrangements. I just needed to be told that the belt-driven alternative isn't realistic so I can stop considering it. The Beta Marine 6/2 genset is a suitable compact marine generator of appropriate power, but its alternator is for 230v AC and to charge a 48v battery I would need to pay an additional £3500+ for an enormous inverter/charger - I'm not seeking AC power at all, I don't need a big inverter, and also the charger I think is limited to 100A. The Sincro E3 2-48/150 is a 48v(to 58v) DC alternator designed to mate axially with an engine in exactly the same way (as far as I can tell) as the 230v AC alternator on the Beta 6/2, and it's a reasonable price. I asked Beta whether they could supply exactly the same engine, either on its own or with that DC alternator or equivalent, but they don't do any other alternators and haven't even answered about just supplying an engine. The point is that the "proper marine generator" Beta 6/2 appears to comprise a Kubota BZ482 engine and a regulated alternator, plus the usual engine start/stop/instrumentation gear, so what is the difference between buying that off the shelf and buying a Kubota Z482, a different regulated alternator, and equivalent engine start/stop/instrumentation gear? (As far as I can tell, Beta's engine control equipment is off the shelf from a third party supplier anyway.) I appreciate that lower-voltage alternators have heavier windings and may be less efficient and hence I may need a more powerful engine for given output. That's why I've been researching the next two Kubota models up too (one of which is the engine used by Beta for their 11/2 genset, the next one up). What I hope I am achieving, however, is to stay as close to a real "proper marine generator" as possible whilst modifying the specification (as little as possible) to meet my identified needs. The issues are around physically fitting the set in the available space, and control of the alternator output to achieve the prompt charge termination that LFP charging requires.

I thought that was exactly what I was trying to do. Perhaps I haven't disclosed enough to be clear. What I want, in the first place, is a boat that actually goes under its own power, which isn't the case at the moment. I've always had the ambition to convert to electric, for the reasons I've outlined previously. Since I have a severe engine problem already and may have to replace, my original idea to convert the existing engine to a generator is probably scuppered, and in any case it may not have been possible to attach a large alternator to it. I have two other choices: replace with something like a Greenline 20 and convert later to a generator, or replace with a new dedicated engine-alternator combination and take the plunge and go electric now. (Well, over the winter, and before the damned prices go up even more - cheers guys, good to have the grownups at the helm.) That's originally what I intended but I've been influenced by the advice I've received on here (kind-of the point of seeking it) and my research into what's available at what price. I'm prepared to invest but I'm not made of money and I refuse to pay (cannot pay) £30k extra for professional services - I must avoid it through my own wherewithal and careful employment of local specialists, if I'm going to do this. The facts of my engine being broken and of inflation (makes sense to spend now before prices go up more and value of income and savings is eroded further) are forcing the issue as I wasn't envisaging doing any of this for a couple of years. The engine-converted-to-generator option would be more compact but has got disrupted by the issue of the forces involved in attaching a 10kW-input alternator non-axially. I already spotted the trade-off, don't worry @IanD: an axial one would be much better for the engine, but it would take up significant linear space (no less than 770mm, maybe 839mm, depending on the engine size) and there may not physically be space for the motor, as Ian illustrated in his previous post, leaving reasonable space for maintenance access. My boat wouldn't need such a large motor as the one he showed, but that fit is still a major consideration. I already thought of this, including mounting the generator set sideways, and I don't know yet but this is exactly why I've been trying to identify the exact engine/alternator/motor combination so I know the dimensions and can answer these questions. If I have to compromise then I think a belt-drive motor is probably better than opening the large-alternator-lateral-forces box again. As for sideways, presumably the engine would still have to go on the centreline for weight distribution, and the arrangement of the bay is that the alternator will have to go to the left (facing forward). Since it's low down on the engine, the physical constraint is probably going to be the left-side swim: the alternator on the centre-line of the crankshaft won't be anywhere near high enough up to sit on top of the swim. No intention of trying to generate power at that level. The objective is to charge at around 0.3C, that being a trade-off between what's good for the batteries, what will charge them in a reasonable time (the point is partly to minimise the time having a thundering diesel running), and the size of generating capacity I can afford and physically fit in with reasonable maintenance access. The attached graph shows my estimate of what I'll need - I know you are suspicious of theory, Ian, but I had to start somewhere and real-world data does seem to validate these estimates. A bigger boat will need a bigger motor simply because of greater inertia, but who knows what size the drag component of the sides of the boat is? I tend to think the main effort is pushing the water aside at the bow. Anyway, the motor parameters suggested are typical continuous running at no more than 7.5kW, usually <5kW, peak maybe double that - my boat isn't as big as yours (and let's not get into a debate about the impact of length on the drag). Availability of data sheets for those Engiro motors is patchy but I reckon the 205W_12013 will be in the right frame. If there's room for the bloody thing.

That's what I would have thought. @Tony Brooks what do you think about this?

I found a data sheet for the Z482. It's only 338mm long, so that'd be a total of at least 338+432=770mm with the Sincro E3 2-48/150 alternator. The power curve shows 9.2kW at 3000rpm. Peak torque is at 2600rpm. The alternator is supposedly 75% efficient (choosing the lower end of the specified range) at 3/4 load and rated at 150A (getting back on-topic). An LFP battery will absorb charge at a fantastic rate, but that doesn't mean it's good for it so the charging source should be limited. For a 400Ah battery, 150A is 0.375C, but 150A is unlikely to be obtained. If it were, at 75% efficiency that would require an input power at 58v of 11,600kW. Hmm. But 75% efficiency is quoted for 3/4 load, and the current is regulated as well as the voltage, so the coat must be cut according to the cloth UNLESS it turns out I have more space than I thought and I can afford to get a slightly bigger engine. The next one up seems to be the Z602, rated for 12.5kW rather than 9.9kW, which feels more comfortable: 11.5kW at 3000rpm, still a shade under and it's 351mm - a whole 13mm longer. Then there's the D722, 3 cylinders, 14kW at 3000rpm, 407mm - as expected, another cylinder longer. I really need to measure.

Having looked a lot closer at the Engiro range, completely agree with you, 205W_12013 is going to be a lot more comfortable, but those calculations you did, aren't they based on running at those outputs? If I put out 14kW, I'd take off. OK, obv not, but I'd not be doing that except in bursts when manoeuvring. Normal cruising would be less than half that (as established previously), so the typical prop speed would surely also be less than half that, wouldn't it? Also if normal running is well below the full rated speed, would water cooling really be needed? And does it look like I have room for a 17.2" prop?? At a guess, my present one is maybe a 14". (Trust me, the paint is in MUCH better shape after a week's graft.)