magictime

Really? I don't know, but I was erring on the conservative side of Chewbacka's figure of 45W max from an air cooled unit. 2% of 1.5kW being 30W.

Ah maybe that's what WotEver is picturing then. I was picturing air cooled. I accept it would be bonkers to run a stove just to produce a small amount of electricity while not using the heat. I did! Cross posted.

Lost to where? Converted from heat to what?

Eh? The 98% of heat not converted to electricity would remain heat.

I fail to understand 'objections' like these. If - and yes it's a big 'if' - there was a gizmo available that could reliably convert 2% of a stove's heat to electricity for battery charging, costing say £500 or less, I'd buy one like a shot. Assuming a stove generated a modest 1.5 kW of heat on average over a 24 hour period (when in constant use over winter), that would be 2% of 36kWh = 720Wh a day. Nobody would question the usefulness of a solar panel generating that amount of power on an average day in summer. And in terms of keeping a battery bank topped up, what could be better than a silent device using essentially 'free' heat to put in a steady 2-3 amps for 12 hours overnight after the engine or generator has to be switched off? (Not that you'd run an engine or generator for an extra 5 hours a day to put in a diminishing 10-8-6-4-2 amps anyway...)

That was careless of them! Letting him overstay seems the least they could do in the circumstances.

Yes, it was planned. And yes, if CRT had wanted to play hardball rather than showing some flexibility, I suppose they could have tried arguing that it was not 'reasonable in the circumstances' (as per the rules) for me to leave the boat on a visitor mooring for longer than 14 days, since I could have foreseen this being necessary. Thankfully they didn't, either because (a) they didn't think the law would have been on their side, or because (b) they didn't in any case see the need to make a difficult situation worse by insisting that I spend the time immediately before and after brain surgery fretting about the logistics and expense of finding, travelling to/from, and paying for a short-term private mooring. Or quite likely, both of those things.

CRT authorised an overstay of a few weeks for me last year after surgery, no problem. I think I did have to email through my hospital discharge form when I asked to extend it from two weeks to four, but that was all.

Fair enough. If you're not planning to head up north maybe you should just enjoy the extra space and the time/hassle saved by not taking on the one that needs work.

My wife and I live on a 55-footer, find the space perfectly adequate, and wouldn't even consider anything that would restrict our ability to cruise freely around the system. So I'm inclined to say the 45ft, unless you really think it's just too small. Are we talking about two boats that are comparable in price here? Because if so, I'd expect the smaller one to be newer/better equipped/in better nick and hence cheaper to maintain and run (on top of the obvious savings on licence, blacking etc with a smaller boat). Easier to find mooring spaces too.

Yes, we have 200W of solar and are planning to add at least another 165W. Plus we cruise a lot from spring to autumn. It's purely over the winter, when solar drops off a cliff and we cruise much less, where I'm wondering if a generator might be an economical option compared to endless running of the engine while stationary.

Thanks Tony. At a bit of a loss now, and trying to think back to last winter for some 'real world' figures on consumption. I remember spending about £200 a month on diesel, so was probably burning a little over 200 litres - say 220. Maybe 20 of that for propulsion (say 12 hours' cruising), about 100 for heating (Lockgate stove), so about 100 litres for battery charging; 25 litres a week for about 25 hours' charging = 1 litre an hour. I think that's about what I'd concluded from monitoring the contents of the tank. BUT maybe it was actually 1.5 litres in the first hour each day, 1 litre in the second, and 0.5 litres in the third, in which case there'd be little if anything to gain by switching to a petrol gennie for those later stages of charging. ...except that you then have the wear and tear/servicing on the engine to factor in. 25 hours a week for maybe 20 weeks is 500 engine hours! Hmm. I still think there should be a practical way to use a TEG or something to keep the batteries topped up using the stove - three or four amps, 16 or 24 hours a day, would do nicely - but I suspect that's a topic for another thread!

Thanks. I suppose some such 'differential cost analysis' is what, in very rough terms, I'm trying to come up with, but I'm increasingly at a loss as to what assumptions to make about how much diesel per hour my engine is going to be burning while charging batteries. Half a litre, one litre, more? My hunch is 'quite a lot', because apart from anything surely it's generating an awful lot of heat all the time it's running, which is energy that's coming from somewhere. Whereas a suitcase petrol generator should (I think!) be burning something between 250ml and 500ml an hour, ish, to satisfy my batteries' demand for 30A or less of charge.

Well yes, but I need to base that decision on something. (Something along the lines of your 'illustration only' figures, but without the disclaimer - and some reasonable assumption about whether running the engine for an extra hour a day is going to cost me 30p for a third of a litre of diesel, or £1.20 for a litre and a bit!)

I think so... So, say that 400Ah battery bank is at 60% capacity, DoD 160Ah. I run the engine for half an hour and the 100A alternator puts back 50Ah, leaving a DoD of 110Ah. Another half hour and I've gone past the point of 'diminishing returns', where the batteries will no longer take 100A from the alternator because the DoD is now below 100Ah. I switch to the alternator at about the 80% charged/80Ah DoD you illustrate above, and two hours later I'm past the point of diminishing returns for the gennie but with the batteries now close to 95% charged - DoD 20A or so. I'm just trying to square that with what Tony's saying about it typically taking at least four to six hours of engine running to get even to 80% charged on a typical battery bank, and much longer to get to 95%. There's quite a difference between 'one hour' and 'four to six hours' (to get to 80%), and between 'two more hours' and 'much longer' (to get to 95%)! OK, so once a week for a 'full charge', but what about the daily top-up? Are we talking about trying to stay above 75%, 80%, 90%? OK, this is new to me. So there's no efficiency to be gained by switching to a generator that's designed to generate some fraction of one horsepower by burning a litre of petrol every two to four hours, because a 38Hp diesel engine will burn fuel just as slowly if the demand from the batteries is the same? I have to say this doesn't square with my experience of feeding diesel into the engine last winter to charge the batteries, or with any 'guesstimate' I've ever read of what an engine consumes while battery charging. Of course the whole picture looks very different from what I've been assuming if my engine is only going to burn say half a litre of diesel per hour of charging after the first hour. It really would be just wear and tear/servicing costs I had to worry about, rather than fuel costs. Thanks for that... no shortage of food for thought here!

I know batteries reduce their demand as they get towards being fully charged, but what if an 800Ah bank was still going from say 60% of capacity/480Ah to 70% of capacity/560Ah? Would they still demand less than 30A? I didn't think charging was that slow, that early in the process. Yes, I understand this, which is why I wrote 'even if' they could take the full 30A. Get to 80% of fully charged starting from where, sorry? And on a day-to-day basis, how close to fully charged do I want my batteries to be (assuming they get more like a 'full' charge say once a week)? I keep reading about 'typical' battery charging regimes being, say, two hours a day plus more like 8 hours once a week, but maybe that's because people are generally only trying to top up from say 70% to 80% most days? OK, this is where I'm really lost - I thought an engine at tickover basically just burns a set amount of fuel, which (as Alan suggests above) I've always understood to be 1 litre plus per hour? Surely the engine speed can't go below that minimum, whatever the load is when battery charging? Hence the temptation to switch to a gennie where the speed/consumption can dip right down.

It's a semi-trad. As I mentioned in my reply to Alan, we used to have a petrol-outboard boat, so I am conscious of the way fumes can creep into the cabin from the back deck. This used to happen sometimes, setting the carbon monoxide alarm off, even when doing nothing 'wrong' - usually in a lock. I wonder if a re-jig of the gas locker to accommodate two 5L cans and the gennie might be our best option.

The 2-hour figure is wrong. One of the reviewers on the Screwfix site picks up on this, and indeed the instruction manual quotes 4 hours. And that's at full load; I'd never need more than 70% to 'feed' my 30A charger. So a third of a litre per hour's running shouldn't be unrealistic; say 43p per hour vs. maybe three times as much per hour of running the engine. It's good point about the 'free' hot water, but I was still thinking in terms of running the engine for an hour a day, which we generally reckon on being enough for a day's hot water, to handle the first stage of charging. Yes, there are inconveniences involved, but last year it was pretty inconvenient having to get hold of so much diesel every month, given that our winter cruising range was only 30 miles or so and had to fit around stoppages. I don't have a problem with walking to a petrol station once a week or less to fill two 5 litre cans (which used to be a daily task when cruising on our old petrol-outboard boat with a 13 litre tank!)

Sorry, to be clear, do you mean 'about the best you can manage in the absence of shoreline'? Also, presumably it wouldn't actually be running at 70% of max continuous for long at a time if this is right... Really? So most of the time I wouldn't even be putting 30Ah back into the batteries per hour of running? I'm just thinking, very roughly, if the batteries were at 80% when I switched from engine to generator, that would put them maybe 160Ah below capacity, which would suggest running the generator for four hours at 70% of max load just to get them to 95% even if they were capable of taking 30A of charge throughout that time. That seems a heck of a lot. But then it is a big battery bank; when they do conk out on me, I'm wondering if I should be replacing them with something half the size really. (Actually I wouldn't be at all surprised if their capacity is already half what it started at; they are almost six years old.) On the point about 'saving up for a new generator', yes, I'm sure a Honda is better, but it's going to be four times the price and I suspect just the wrong side of being small enough to easily stow out of the way on the back deck. And if I can save maybe £50 a month by burning (say) 7 litres of petrol over the course of 18 hours, rather than (say) 25 litres of diesel, it would pay for itself in its first winter.

Thank you. Am I right in thinking the relevant figures are 700W divided by (say) 14.5V charging voltage = 48 amps going to the batteries from the gennie via the charger, (or say 45 amps allowing for inefficiency) - suggesting I'd want to run it at about 2/3 load? (Only presumably the gennie would actually be putting out more like 3A at 230V, which the charger then has to transform?)

Thanks. I've read that post - it's one of the reasons I have at least some shaky grasp of the basics around multiple stages of charging!

Ah, OK, so the alternator and solar won't be 'routed' through the charger. I guess the alternator is routed through my Sterling 'Alternator to Battery Charger' instead. That makes sense. So, next question: I'm considering buying a very small suitcase-style petrol generator, the 700W Impax model from Screwfix. Am I right in thinking that this should be more than adequate for the 30A charger I have? Over the winter, when solar is no longer contributing anything worthwhile, I'm thinking along the lines of running the engine for say an hour a day, to do the 'heavy lifting' during the bulk stage of charging, then switching over to a generator for a further hour or three a day, as needed, plus six or eight hours once a week. We'll be CCing 'off grid' so shoreline is not an option. Am I right in thinking this should be a lot more economical with fuel? Last winter we were running the engine three hours a day and the amount of diesel we got through, between that and our Lockgate stove, was outrageous!

Sorry, I know there are loads of threads on battery charging on here and I have had a good trawl through them, but I still don't exactly feel on top of the subject! My immediate question is this: I have a whacking great Bank of Trojans, 800+ Ah when new, two alternators rated at (I think) 110A for the domestic bank and 70A for the starter, a solar charge controller rated for 40A (though not yet enough panels to deliver that).... BUT my Sterling battery charger is rated at 30A. I understand that as my batteries get past 80% charge or so they won't be able to take loads of amps anyway, but does that 30A rating mean they're never going to get more than 30A, regardless of how many amps the alternator or solar panels are able to supply during the early stages of charging? I'm wondering if my charger is a bit of a weak link.

And you try stabbing a postman's hand when he puts a piece of junk mail through your letterbox and see what happens! Goddamn bleeding-heart do-gooder pinko liberal lefties with their so-called 'human rights'.

Just for a bit of balance here: Yes, you want an appropriate anchor, chart(s) and lifejackets for the reasons explained above. Yes, you want to take advice from the lock keepers about tide times and conditions (some tides are gentler than others!) BUT - for years we've had this picture in our heads of a hair-raising ride along a fast-flowing, choppy river, full of hidden sandbanks etc. at random locations below the surface, and navigable only with the aid of mysterious 'charts' intelligible only to the saltiest of sea-dogs. Well, we've just come up the Trent from Keady Lock to Cromwell Lock, with an overnight stop at Torksey, and it wasn't like that at all. We were moving at a normal speed, on calm water, and 99% of the time the charts were simply reinforcing the general rule that you should go round the outside of bends rather than cutting corners. So as I say, yes, be prepared, be equipped, be cautious about the conditions you travel in, but don't allow yourself to be completely intimidated by worst-case scenarios.