Tony1

I'm wondering if I can prompt a discussion about the costs vs benefits of solar hot water, via a question: Imagine two boaters install identical sets of lithium batteries, and they use identical amounts of charge each day for their 'normal' systems, apart from one thing- boater A also uses his batteries and inverter to power the immersion heater (for say 50% of the year). Lets assume purely for discussion purposes that boater A is handsome and dashing, and boater B is a grimy troglodyte. And just for discussion, lets say that in heating up his water, boater A cycles 50% more energy through his batteries each day than boater B. So over a year, boater A is making his batteries cycle through 25% more energy than boater B. But here is the burning question- will the troglodyte boater B's batteries last 25% longer than those of the handsome boater A? It's one thing for us dashing solar hot water bods to count our savings in terms of engine running and diesel costs etc, but if our batteries only last 7 years instead of 10, are we really making a saving? Asking for a (handsome) friend.

Apologies to the OP for banging on about solar again, as I know its been mentioned, but it is worth reiterating for a liveaboard. On 12 of the last 15 days I've had enough solar to run most of the electrics, and if I didnt run a fridge it would have been every single day. Today I got over 1700Wh of charge (charging at about 13.35v), so if I understand it right that means I got around 127Ah of charge, which is my full days usage in winter. It was a bright day, but not sunny all day long. And I am overlooked by trees to the north and east, so its not even the ideal spot for solar. If I'm already getting 130Ah of charge in a half decent day around mid Feb, that says to me that that its worth you rearranging the coal storage on the roof (ie pile the bags up higher), and getting some more panels installed. If you were getting that same amount of charge (charging with a genny or a B2B at say 40 amps), that's three hours of engine or genny running saved, in terms of fuel costs. And that's just one day. When we get into Spring the solar will go ballistic I never heard of a single liveaboard boater who regretted installing more panels.

My BSS is coming up in December, and the last thing I want is to get one of those jobsworth types who have a bee in their bonnet about about some particular issue. I was going to replace my mushrooms with flying saucer vents but I dont think I'll bother until after the inspection. Are there any examiners in the North west that folks would recommend as being a bit more reasonable and pragmatic?

You know what- the truth is I dont know- at least in the sense that I dont know exactly what the chargers are doing to the batteries during the float phase. I never use the float phase in reality, since I switch the chargers off at 85% SoC. I've messed around with the float phase a few times (eg in Llangollen), and my impression is that although the charger is not charging as such, it is sort of 'leaning' on the batteries, checking the voltage in case they need a bit more charge. And if the battery voltage drops a bit below the nominated float voltage, the charger seemed to kick in and start doing some limited charging. That was the 6 year old shore charger mind. I dont know how other units and MPPTs etc behave. I agree with you (from the things I've read) that the ideal treatment for lithiums is to just charge them and leave them alone, ie switch off the charger altogether. No float charge needed. Thats why I like my SoC-based charge management using the BMV712. It seems odd that such a basic principle- something that a relative newbie like me realised very early on in my usage- still isnt being built into the charging products that we are seeing come onto the market. My solution is to set the float voltage at 12.7v, and in fact I may go even lower.

I definitely agree with that. My charging voltages vary wildly, from 5 amps of solar in mid December, around 75 amps with the engine running, up to potentially 170 amps in summer with MPPTs and B2Bs all running. So it would be impossible in my case to set a voltage that could always guarantee you that you stop charging at a chosen SoC. By coincidence, I had to rely on voltage to manage charging for the ten days I spent in Llangollen, as my shore charger doesnt have an input for a remote BMS switch off, so my BMV712 couldnt be used to control it. And it was quite tricky. I tried 13.8v and found that the SoC was going well over 90% before it went into float. Then I tried 13.7v, and then it only charged to 70% before stopping. It was tricky to find a good setting with it.

What I'm trying to clarify is more for new lithium users, and its not so much about the specific charge voltage you choose (in fact I agree with your suggested values for a prolonged charge). My issue is this- I think potential new lithium users might get the idea that if they set their MPPT to bulk charge at 14.6v, then as soon as the sun appears above the horizon and a few amps trickle in, their battery voltage reading will jump to 14.6v, and it will stay there as the battery fills up, until the MPPT goes into float. But what actually happens, as you obviously know, is that the battery voltage increases very slowly. If 20 amps are coming in, for example, my battery voltage will stay under 13.3v for a long time. If I charge at 60 or 70 amps, the battery voltage will be maybe 13.4 or 13.5. I dont use voltage to manage the charging like almost everyone else does- but (to make it more pertinent to newbies) if I did use voltage, my battery voltage would creep up very slowly until it reached the bulk charge voltage value (lets say 13.8v), at which point the chargers would go into float. So my point was just to clarify that when people set a bulk charging voltage, that voltage will take time to be reached. And when it is reached, the charger will go into float. In other words, the bulk charge voltage, is an 'end point' voltage, it is not a voltage that is maintained throughout the charge. I dont think a lot of lithium newbies are clear about that.

I'm sure I'm missing something here, but I wanted to check- in the OPs case he is charging at a modest 40 amps, So even if he sets his charging voltage at 14.0v, his battery voltage will not actually reach 14v until the battery is say 90% full, surely? And when it reaches that point, wont his charger go into float mode? And if he restarts his engine after a stop, the B2B will detect the battery voltage is already high, and it will stay in float, right? Thats the way mine seem to work, at least from observing them. When I charge at 40amps or so, the battery voltage doesnt even go above 13.8 until well into the charge, when the batteries are at about 70 to 80% full. My MPPTs are set to charge at 14.6v, but in reality the batteries stay around 13.4 or 13.5, increasing very slowly, until they are 70% full. In my experience, the bulk charge voltage seems to be an end point or target that is used to decide when to go into float, right? It's not a voltage that is sustained throughout the charge. I guess with your alternator charging at 160amps or more, you do see a really significant voltage rise as soon as you start charging, but I dont see that (until summer), and I dont think the OP will. I'm not sure if I've asked a question in all that! 😁

They are Valence batteries, made for EVs. The idea was you put lots of them in a vehicle but you only need one BMS module, which is a separate item. So they didnt fit a BMS in each battery because for the intended purpose, they didnt need one. You could install a BMS, there are a few videos giving some guidance, but I just didnt fancy it:

To be honest the high and low voltage disconnects are only there because I have ex-EV batteries which dont have a built in BMS with an emergency disconnect. So they are the last-ditch emergency measures that you hope wont ever be used (other than me testing them). But my SoC monitor also provides some protection, in that it will remotely switch off the chargers if the SoC gets too high. The final protective measure is the normal thing of the charging profile set on the chargers, which will ensure that they go into float once the battery voltage gets to 14.6v. It looks horrendously complicated, and there are more blinking lights than the bridge of the Enterprise. I think the electrical cupboard is now so complex it has become self aware, and its trying to absorb my intelligence.

Nick knows my setup pretty well because he very kindly advised me on how to wire it all. It got to the point of 'where do I connect that red wire?' .....

I heard that he does have a BEP switch, but its not involved in charging - apparently he uses that as an emergency disconnect for the loads, if/when the voltage ever gets too low. Some say he even has a separate disconnect in the event of a high voltage event, but that one only disconnects the chargers, and leaves the loads working. The story goes that he bought a victron battery protect to act as a low voltage emergency disconnect, but then found that the thing doesn't work with inverters. Apparently he was fuming when he found that out. So the cunning devil used his new 'battery protect' as a high voltage disconnect instead (controlled by a BMV712), and he used his BEP switch as the low voltage disconnect. At least that's what I heard.....

What he said 🤣 Thanks Nick, I would have given the poor chap some ill-defined guff, but that was much more clear and concise. As I understand it, you cant take current directly from an alternator into a B2B charger (and then to the lithiums)- you need a lead acid in the setup. ETA- I'm not sure if this device allows an exception to that statement above. It looks as if it connects to the output of an A2B charger, and can then connects directly to the lithium batteries, and can thus manage the charging in a safe way for lithium batteries, without the need for a lead acid battery in the 'chain'. So an alternative to a B2B charger for some folks, maybe? https://sterling-power.com/products/multi-chemistry-battery-charging-module That said, I dont mind having a lead acid in the charging train- it feels like it gives a bit more safety in that if the lithiums are suddenly disconnected for some reason, the alternator isnt put at risk of damage.

Tbh, if I ever flogged my boat, I'd remove the lithium batteries plus related gear, and buy with three mid range lead acid batteries plus a suitable device to manage charging them from the alternator. Keep it all simple. There are a fair few boaters who aren't fussed at all about lithium batteries, and I suspect that the presence of expensive lithium batteries and any associated gear might not be reflected in the sale price. Also, the replacement boat probably wouldn't have lithium, so it might make sense to take that sort of gear with you.

We already have a bit of kit for the job- its the BMV712 (although it was very much Mr Norman's advice that allowed me to set it up). I've set my BMV712 so that when the battery SoC rises to the target value (usually 85%), the internal relay on the BMV712 sends a 12v signal to all the chargers via a very small gauge wire, and that tells them to switch off safely, rather than just disconnecting the charge cable, which sounds a bit 'heavy handed'. When the battery SoC falls to the appropriate level, the BMV712 sends another signal, and that will restart the charging units. The victron and sterling chargers (including the MPPTs) have a port (called BMS), where you insert the wire. Bish bosh, as they say. (Well almost bish bosh. My shoreline charger doesnt have an input for a BMS remote switch off, so I have to rely on setting a charge voltage, but I'm very rarely on shore power so I can live with that. )

Nick mentioned above the BMV712 battery monitor device from victron. I think it won't be long before you get one of these, or something similar. You enter your battery capacity etc, and then you synchronise the battery monitor by charging the battery up to 100%. The monitor then measures all the current inputs and outputs, so it keeps a pretty accurate idea of how full your battery is. The thing is that you cant really rely on the resting battery voltage to tell you what the SoC is in the battery. For example, at 70% full the resting voltage will be around 13.20 (probably varies slightly depending on the battery). By the time the SoC gets down to say 40%, the voltage will be reading 13.10v. So you can see that for a lot of the range, the battery voltage doesnt change much compared to the SoC, and thus the voltage cant really be relied on to inform you accurately about the SoC. For this reason, I agree with Nick that its a very good idea to buy a battery monitor that measures current inputs and outputs. The accuracy does drift a bit over time, so its not gospel. And you should resynchronise every few weeks if you want it to stay really accurate. But the point is that on a day to day basis, using one of these monitors to check your SoC is much easier than trying to use the voltage. The victron BMV700 and BMV712 are well over £100, but there seem to be some much cheaper units available on Amazon, that do seem to get good reviews.

Obviously that's all 100% correct, and I think the real thrust of the idea that I would try to get into the OPs head at this very early stage is to keep an eye on the batteries from the moment you get aboard. And all the more so if there are no solar panels to help the batteries, since the boat will probably have been left unoccupied for several weeks or months before he turns up. I just blithely assumed my batteries would be ok, if I even thought of them at all- and new boaters need to understand that this is not the case, and they need to be aware of the battery state immediately. There will be different things to keep an eye on as you say, and hopefully the OP will develop some sort of checklist and will work on getting some knowledge about batteries, in advance of the big day when he steps aboard.

Just to echo the general theme, engine and electrics. And specifically, find out what engine you've got and there'll probably be a youtube video on how you service it. If there isn't, get a pro to do the first service, but only on the understanding that they explain the steps to you as they go- you can offer a few more quid as this will slow them down a fair bit. You can also video them doing the service so you have something to refer back to. Fees do vary wildly, but I've been asked for almost £200 to do an engine service including alternator belts, and you very quickly realise that there's a lot of money you can save by doing the servicing yourself. The thing about the batteries is that you need to be aware of their state literally within minutes of you first moving onto the boat. I didnt look at my batteries until the second day, and by then they had already been over-discharged and probably damaged by my ignorance, and the cost of those mistakes will be a few hundred quid for a new set. So check the battery voltage when you get aboard, and keep an eye on it every hour or so throughout the first few days.

I would personally prefer no float stage- as you say that is a lead acid procedure that has been carried over and is not needed. I do set my float to 13.15v, but I do get the impression that even then, the chargers are periodically trying to apply a very small charge, so I might reduce my float values down to 13.0 or even less. One of the things I like about my SoC-based charging management is that at 85% SoC, all the chargers are switched off (no float), and I have a suspicion that this allows the battery voltage to fall more naturally than if the charger is still awake, and is periodically prodding the battery to see what voltage its at.

I suspect what you'll find when charging at a relatively low rate of about 40 amps (plus some from the solar) is that during the charge, the battery voltage won't get up anywhere near the nominated charging voltage for a long time. For example, I have my MPPTs set to charge at 14.4v, but in winter the battery never gets anywhere that voltage, until the end of the charge and when the batteries are over 85% full. Its different when I charge in high summer, with the MPPTs putting in say 90 amps. So charging at a higher current seems to push up the battery voltage more quickly than charging at low current, and you reach your end point a bit sooner. I find that the charging voltage is a sort of target/end point figure, and you set it according to how full you want the batteries to get. So if I set my bulk charge voltage at 14.6, the batteries will get above 95% full before the chargers go in to float. If I set the charging voltage at say 13.8v, the batteries get to about 80% full before the float stage starts. Maybe think of the bulk charge voltage as the thing that determines how full you want the batteries to get.

That's interesting, that you are thinking of bringing your lithiums indoors. Opinion seems very divided. Lots of people whose opinion I respect think its fine if you keep them in the engine bay, especially if you have warming mats underneath them (which are powered by the batteries themselves. But I still have sneaking doubts about it. If for example I get up at 7.30 on a winter morning and the engine bay is at minus 5 degrees, and if I switch on my 1000 watt 240v mini kettle, that will draw at least 80 amps from the batteries, which is the largest load they ever get in normal use- is that definitely, definitely ok? If the mats keep the whole battery above zero (or whatever the current official policy is - someone will be along to clarify the most recent advice), then you would imagine even an 80 amp load wont damage the batteries. Certainly we're not hearing stories on here about lithiums being damaged by putting loads on them at very low temperatures, so it must be ok. right? But personally- and admittedly more from superstition than facts- I'm keeping mine in the cabin for the time being.

I thought you might be interested as you've got one of these things- I've just installed the victron 30 amp B2B unit and run it for 50 mins, and you are absolutely right- it does get very hot. The fins at the back are too hot to touch for more than a second or two, and even the main case of the unit gets uncomfortably hot to the touch. I can see why people recommend pointing a fan at it. You have to wonder how hot the internals are getting for the case to be so hot- but they sell shedloads of them, and the campervan/motorhome folks love them. If there was a real risk, we'd be seeing campervans in flames by the score up and down the country. The victron unit gets as hot as the BB1260, but the BB1260 has a fan, so in theory it dissipates its heat quicker and better. On the plus side, the victron unit didnt throttle back its current output once during the 50 min run, so I think as long as my nerves can stand it running so hot, it should be fine. I'm not going to get another one of them yet, though, I think I'll give it another week or two before deciding whether to sell the good BB1260 and replace it with another victron unit. One point I will make in favour of the BB1260- it kept up its half-power 29.6 amp charge rock steady throughout (as it always does to be fair), whereas the victron units seem to slightly reduce their output as the battery voltage starts to creep up during the charge. The output only reduces by a couple of amps, but you would rather it stay constant. So I think there is a decent chance your unit is getting a bit overheated in the engine bay, and you might see less frequent throttling down if you could install it somewhere cooler? Perhaps you could take the cables and the B2B through to the cabin somewhere?

Yes, an upgraded alternator plus a controller like the alpha pro was definitely the route I should have gone down, and its what I would always recommend for people looking to get more charging current from their engine. BUT my canaline 38 doesnt have a poly V belt, and it would have needed a crank upgrade before I could fit a more powerful alternator. And I had already started spending money on the B2Bs. Given that I only need engine charging anyway on about 90-100 days per year (because of all the solar panels), I couldn't justify the very significant expense of the crank upgrade, the controller, plus a new alternator. If I ever buy another boat, one of the things that will always be on my must have list is a decent alternator with a poly V belt, so that I only need the alpha pro fitting in order to be ready for a lithium battery install.

Thanks for the reminder Francis, and I admit I am a bit concerned that the victron units will be no better, and might even be worse, in terms of heating issues. That's why I don't just want to rubbish the BB1260s as such. As I said, the BB1230 (30amp) unit has run faultlessly whenever needed, it is a truly excellent and highly versatile unit that I would recommend to anyone. But I guess B2Bs with larger current outputs like the BB1260 are a bit prone to heating issues? My cunning plan is to try out one of the victron 30 amp units for a week or so, and see if there are any heating issues. I was optimistic because the 18 amp victron unit seems to run really well with no overheating issues, but we'll see. Maybe 30 amps is a different matter to manage with just cooling fins and no actual fan....

I have large vents in the top and bottom of the cupboard door, and I fitted an extractor fan into the top of it, so there's no cooling issue- and out of habit I leave that door open anyway whenever the B2Bs are running. But you are right, its worth a try with Sterling- there is a chance it'll be an easy fix. But it wont be any kind of user setup/config issue. Both of the BB1260s are set up identically for every parameter, and they are running from very similar alternators and lead acids that are in decent nick, and yet only one of them is now working. I've never been over the moon with the products tbh. They made them super configurable and versatile, but even when working, neither of mine two units will run at full power for more than about 10 minutes before they throttle down to about 30 amps for a few minutes, presumably to cool off. I admire what they tried to do with these units, but in my view they didnt quite pull it off in terms of managing the heat output, and I always felt happier running them at half power, which still yields 30 amps but they behave much more consistently. I did try talking to them about the heat issue a long time ago, and I explained that after about 10 minutes, the cooling fan would come on, and at that exact moment, the current output would be reduced to about 30 amps. The guy ignored my suspicion about it being related to cooling, and instead he felt that it was more likely to be an issue related to the input and output voltages (if I remember correctly), and I just gave up the discussion in the end, because they were working well on the half power setting, and doing the job I needed. Or at least they were working until yesterday. The behaviour I'm seeing in the dodgy one now is a different thing again, but anyway, worth asking for their thoughts about it, as you say. To be fair the BB1230 has performed faultlessly so I'm not rubbishing all their products, or their service. They will try to help and diagnose stuff, and these days that's not a common thing. I've heard bad things about Renogy's customer service for example, whereas with Sterling you can always talk to someone who knows their stuff. That said, even if it gets repaired, I'm fed up with the BB1260s, and I would prefer to just get all the Sterling products off my boat tbh, and get some victron units instead.

This is a grey area for me, thanks for clarifying. I had assumed that if you have a valid CRT license when you went into the marina, and if you can prove to CRT that you held the marina mooring for x months, then you could state to CRT that you never left the marina, and thereby you would be able to claim back the number of months from your CRT license fee that you spent static in the marina. I didnt know you had to pay the CRT license fee even if you never left your marina.