captain flint

regarding voltage drop and cable thickness, 12V planet seems to think I would be OK but goshdarn it I feel sure Alan et al know what they're on about and of course I don't want to order something then find it doesn't work. Ah well, as predicted, I'm possibly more confused now having asked for help on here than I was when I started. But I'd like to think it's a marginally superior quality of confusion

Oh flipping eck I did it again. I am perfectly clear what one is and the other but I have this brain fart thing, something like dyslexia or something*, where when a word starts or ends similarly to another I sometimes interchange them! Sorry. I once said "helicopter" when I meant "hospital" * probably just stupidity Anyway I'm going to edit it now just for clarity, the blushing I can take ta! Thanks again Alan. Although I would like a 12V fridge I think changing the cable neatly would be very tricky (I'll get some advice on this), and although I am intrigued by Magnetman's ingenious sounding battery idea it just seems a bit bodge-y to me (not that I know).. So I'll probably just get a 230V number. Or just stick with the old one I have. It keeps things coldish, even on its stingy cable I see there are Dometic fridges that switch to AC when the inverter is on and use 12V when it isn't. Might that be a decent solution for minimising draw when I'm not on board - even with the odd voltage drop?

Its a 6mm2 wire. Are you saying the battery would be kept charged because of the discrepancy in voltage, no actual charger required?

Amazing info, thanks Alan. I expect I missed 3 strands and it's 84 at 0.3mm then. TBH I think it's less than 7m. But I think it's more than 6. All in all I'm probably changing my mind and now leaning towards an efficient 230V fridge. There's a socket right there. My inverter says it's zero load power is 13W so I think that means draws just under 1.1A per hour/ c 26 amps per day . I'm not sure whether the eco mode ("AES") on my inverter - zero load power 9W - will be up to snuff for running a fridge - and others seem a bit confused about that, too . But I figure if I find a highly efficient 230V fridge I might be best off going down that route, even leaving the inverter on "normal" mode. I haven't been in the habit of leaving my alternator inverter on the whole time so far, but maybe it's not such a big deal. I guess I just worry a little about being away for a few overcast days during summer. But my 560Ah LiFePO4 set up with new inverter should be able to cope with a few days I guess.

Good luck, if it lasts as long as your last then it will be doing pretty well I guess! I was wrong about mine, it's not a Coolmatic. It's a Coolzone (?!). It has a danfoss but the fridge itself is pretty cheap and cheerful, not very well insulated

My multi strand cable has 81 strands. I'll properly measure one of the strands with a micrometer when I get the chance (and before I take any decision), but as a rough estimate, 3 lined up very carefully are just about 1mm, 4 are way over, and 0.3mm is a fairly standard diameter for these things according to a couple of cable manufacturers. If each strand is 0.3mm then my cable would be 5.725 mm2. It should ideally be more like 6 or maybe 7mm2, you but I guess I'm wondering if such a small shortfall will make a big difference to things. Not sure anyone can answer that but you never know The installer told me no need for me to recalibrate, but that I should charge them up fully every now and then to keep readings accurate

I'll probably stick with a fridge (if nothing else I will just keep the old one I am currently running) as I don't shop every day. But thanks for the tip.

Ah. yes. Good point. Ta.

Thanks, Tracy! Yeah, I found this table useful. I do hope it's correct, as that would mean it looks like my cables are about right So after a little learning, I'm thinking my cables should in fact be OK, and I am leaning towards a 12V fridge. Problem I have is every time I read which people like, and think, right then, the consensus seems to be Inlander/Shoreline/Dometic/Whatever is the way forward, I find a post saying, "Well, our Inlander/Shoreline/Dometic/Whatever was utter rubbish and broke down all the time." Ah well. You shouldn't ask for people's opinions if you don't want a range of views. At least it's not as bad as wood finishes. I swear, I have 3 friends who are all really experienced professional carpenters, and any time I ask them about finishes, they will say, "Well, for what you need here, loads of people would say X or Y but they all all 100% wrong for these [very impressive sounding] reasons. What you want is Z". But of course they never agree with each other!

weeeelll.. I mean. I know how much cable sticks out at each end. I can measure that. Then I can measure the travel round the cabin sides from one hole where they go into the cabin lining to the other hole where they come out. Of course, they might be meandering all over the place in there. I can't see. But I bet they aren't, at least not much. And really, whilst acknowledging my profound ignorance about the technical stuff we're discussing here, I'm hazarding a guess that this sort of measurement-assisted estimate is good enough for our purposes here. I mean, I don't want to do down the ingenuity and knowhow that goes into canal boats, but it's not NASA, right? According to that rough measurement it's 6m but I called it 6-7 to account for the fact I can't actually see all the cable yeah as per my previous message to Alan the diameter including insulation is more 5mm, the diameter of the copper itself is 3mm. Well, obviously, measuring diameter with a steel rule is not exactly an exact science, but I'm saying 3mm near as hot dammit. Thanks!

I have no idea where to find a battery's knees. I guess I'll have to do some googling... Ah, right, well in my case the diameter of the copper is 3mm. c. 5mm plus the sheathing Turned it off at the fuse box and got my steel rule onto the little bit of exposed copper I can see at the little junction box thingy

Thanks for your post, your points all sound sensible to me, and I even understood most of them. Help me out here, though, can you say this one again in a slightly different way as I kind of think I know what that means but I'm not sure (I'm guessing in practice you mean continuing to charge them when they're getting nearly full... ?)

'Ere, Alan. I'm not doubting you may be right about this and that I may have the wrong end of the stick in some way, but that's not what it seems to say here

Thanks, Alan. Kind of what I was expecting to hear but with some extra info, I was ignorant about CSA vs diameter, so that's another tiny (and very basic) chip off the enormous rock of my ignorance. Ah well. It was nice to dream of a new fridge. But I guess now I need to focus on dreaming of new cables, first. I wish I could be advised online about the best way to replace my fridge cables, but I think it's the kind of thing you really need to be on board in person to be able to say anything much sensible, right.

Question. Very very hopeful and probably silly question. To which I can guess the answer: Looking on the data sheet for the danvoss compressor that is in my fridge, it says 6mm cable for 6m travel on a 12V system. This does mean two cables of 6mm each, rather than 6mm in total (ie 2 x 3mm), right? I'm sure it does but I would hate to make that assumption if in fact my 2x3mm cables are sufficient... Chance would be a fine thing Every statement on this forum comes with an advisory. As do most statements about most things in life, really! Nevertheless it is a useful resource and there's as much wheat as chaff, in general, I reckon. As it happens my installer kind of agreed. He said not to be worried about charging or depleting it more and that the cells will last for years and years and year even with regular heavy-handed treatment, but that the sweet spot for the longest life possible for them is 30-70%. It's like you're both right - it doesn't matter that much, but it does make some difference (according to Phil Owen, anyway)

I've usually not run 230V applicances all the time, and only turned the invertor on when I need to. But with my new batteries I can see I may get into the habit of leaving it on when I'm on board as I've plenty more wriggle room on power and the new invertor is more efficient than the old in terms of draw. I suppose the question of warm but overcast summer days when I'm away for a couple of nights and would like to leave the fridge on might be pertinent here and make me lean towards a 12V fridge Don't bank on that - I changed my 'old' 12v fridge for a 'new' 12v fridge and it wouldn't run. The new fridge was more sensitive to volt drop so I had to re-run the cables in a much larger size to get the new fridge to work. Hmmmm. Thank you for sharing this. I've been looking at the wiring and am typically very confused. But I have a feeling this might be the single biggest obstacle and might even make me just stick with the devil I know. The cables are 3mm* and the travel is 6 or 7** metres. So - I think? - the cables are maybe half what they should be? *Nothing printed on the sheath, but, well, they're 3mm. **This is a sort of measured estimate - cables come out of the back of the fuse box, disappear behind the cabin lining, and reappear behind the fridge. So, hard to say exactly how long they are but I measured the travel plus the bits sticking out behind the fridge. It's is on the other side of the boat from the fuse box. My uneducated guess is that while in theory you might be able to use the thin cable to pull a fatter cable from fusebox to fridge, in reality it's unlikely to work on such a long and potentially tricky travel (?). In which case I'd have to think about a whole new travel for new cables. Not impossible, I'm sure, but not the same as simply disconnecting one fridge and putting a new one onto the same connection.

They have a very decent BMS.The installer just got back to me and said that keeping them between 30% and 70% is the sweet spot for the longest life but that they are very tolerant and not to overthink it every day. IE a good general rule that's basically fine to break now and then, like giving them a good charge before going away for a few days Thank you

What I'm about to type won't please anyone less technically illiterate than me, but Phil Owen who installed my system claims the set up he's designed (utilising a Victron Cerbo CX) is the only on board system that is absolutely reliable and accurate when it comes to battery usage, and claims to have tested it (for more info about it follow the link to his page in my original post). Today, I've not had the engine on, not had much sunshine, fridge has been on all day, and the readout is down from 87% to 85%. Presumably overnight it will take a few more percent off. It's only just been installed or I'd have a clearer idea. I should have said how much I'm away - normally one or two nights, sometimes 3. If I'm going away longer than that I would empty the fridge and turn it off, at least until I have ascertained that I can afford to leave it longer. I appreciate that I'm just taking the word of the magic box and the reassurances of the installer that it's reliably accurate, but, um, er. Um. I'm feeling right now that it should be OK? In principle, though I'm right with you when you say it doesn't matter which type of battery you have, you need to put in what you take out, of course! Goddammit I don't know. I always used to turn it off when I went away. Why change? Maybe milk. Um. Christ. Glad you asked. I will just turn it off. Duh.

correct

hmmm. I knew about the taking them down to 20% but thanks for telling me about only charging to 80% - can't believe I didn't come across this before, I spent days reading up on things before making such a big decision, but wasn't aware of that. I'll make an enquiry with the installer.

Doh! Yes indeed. Thanks for pointing out, now edited

So... I've been reading many threads here on this subject and if anything I'm just more confused than before. Although maybe a better quality of confusion. Maybe. First off, I will own up right now to being immensely thick when it comes to electricity. Apparently I'm capable of not being entirely stupid about a few other things (then again maybe that's just people being "nice"). But electricity, my brain just freezes over. I expect this is the primary problem and I that many will sensibly point out getting to grips with the basics is really essential. But I'm going to blunder stupidly on anyway. Feel free to sling abuse. I can take it. I have an old (15y) Coolmatic 12V fridge. It runs OK ish but somewhat less well as the seal isn't as good as the door doesn't sit quite straight after the hinge got damaged in, uh, a small boat fire (Long story. Not caused by onboard equipment). Plus it's noisy (sounds like the Tardis). And I'm keen to give it to a friend who is short of money (and a fridge). And I'd just like to get a better one. Feel free to point and laugh, but the fact is I have a stupidly expensive OTT electric set up. Inverter: New Victron Multiplus 2 - nominally - 3kW inverter charger (output drops to - nominally - 1.7kW at highest operating tempratures). I'm not exactly clear on how much power it draws just by being on. I've looked in the manual and it says 13W, but, well, I think I said something about being stupid, no? Battery: New LiFeP04 battery set up giving 560Ah. I guess the obvious thing would be to get a very efficient 230V fridge and leave the inverter on. But apart from force of habit, I guess it just feels more streamlined and efficient to go with a 12V fridge, plus less to go wrong. A few other reasons I'm thinking of forking out more on a 12V fridge: - No new wiring needed (it wouldn't be all that easy running a new wire due to how things are set up) - Although I have overkill on my electrics, I'm used to only switching the inverter on when I need it - plus I'm away for a few days at a time most weeks. I prefer to leave my fridge on the whole time, rather than switching it off at night/using it less in winter. I'm no stranger to living like that on board, and I get that it's an option). I want to look after my fancy battery as much as I failed to look after my last lead acid ones - I suspect the chances of an inverter fire are small... But still, even the fire I had was quiet enough thank you. It's nice to come home and find it still there. On the other hand: - I always leave the batteries charged up before I go away, so my new overkill set up could most likely cope without running them down even with the fridge left on (?) - I do have 800+W solar (but not angled and in winter, only giving a little bit)Plus, any power saved feels like power I could use for something else, some time. I think my fridge and my laptop are the only regular big power draws, but there are plenty of other things I might like to get in future (hen I have saved up some more spending money - it's all going to be gone pretty soon...!) All in all I don't mind forking out the extra for 12V (so long as the new fridge lasts several years). But if I can be persuaded that's stupid and I should just leave the inverter on I guess maybe I would go that way. Am I being stubborn to think a decent 12V fridge is more elegantly efficient and with fewer possible issues? Should I bite the bullet and leave my inverter on the whole time, even when I'm away? Go on. Do your worst Thanks!

I ordered some plastic coated 4mm steel cable (6mm including the plastic coating) , 60cm long, with a loop at each end. It's been brilliant. I can wiggle it through little gaps too small for my mooring chain links to get through. Brilliant, that is, until I left it on the towpath somewhere.

Oof! I've put the whole thing out of my mind. Um, I did some research and used what I thought seemed easiest and most like what used to be allowable for tank blacking. I thin it may have been Black Jack. It went on very glossy, whatever it was, which is probably entirely unimportant abd uninteresting. I can't really say what the tank is like now, as I've bolted it back shut, and hope to never look in it again! (yes, yes, I will be opening it and doing it again in a few years but I'd rather not think about that thanks). I did empty my tank recently and the water ran clear right to the end, which is an encouraging sign of the coating holding up ok, but it's only been just over a year, so I'd hope so, too! Do use a proper filtering mask thing with cartridges. An experienced and professional boat chap, who's even supposedly a mate of mine, said, with a fan blowing in, a regular mask and goggles should be fine. It isn't, you want the proper filters, you really do. I did half a day without. Not good.

Wow! So it treats it then you can just dump it? And is it environmentally friendly I wonder?