nicknorman

If the decline was gradual, I’d say limescale on the calorifier heater pipes. The trouble is that it will be on the outside of the pipes, on the potable hot water side, not inside from the coolant circulation. So descaling is a bit tricky as you have to pour nasty chemicals into the hot water supply. Lots and lots of rinsing out required! If the calorifier has an electric immersion heater element, you could undo this which allows you to look inside at the state of the heating coil pipes and see if there is a lot of limescale.

Having seen the data you recently posted I can see why you are taking the line you do. But if that is typical data from your setup, that is abnormal and points to something horribly wrong with your system. Obviously you are in denial about it at the moment but you will find out eventually. And when you do I’m sure you will keep quiet about it. As to using emotive words like “safe” and “invalidate … guarantee”, if a battery really is out of top balance, this is not unsafe nor going to invalidate a guarantee, this is scaremongering. All it means is that the capacity of the battery is temporarily reduced. No damage is accrued and the situation is entirely reversible. Not a scary situation. Well as we’ve said voltage differences at 75% SoC are not relevant to anything. Obviously “out of balance” is not a binary thing. I’d say out of balance becomes significant if the BMS protection kicks in due to one cell going overvoltage at the chosen charge voltage. So the higher the charge voltage and therefore the more determination to cram as much charge into the battery as possible, the more important it is to have the cells well balanced.

Yes. Passive balancing uses resistors to dump energy from the higher cells. Active balancing redistributes the energy from the higher cells to the lower ones. But is more complicated and expensive. Since good quality well set up cells don’t really go out of top balance(!), boat type systems generally use passive balancing. The main advantage of active balancing is if you want to maximise the capacity of the battery, ie have it top balanced AND bottom balanced, so you can fully discharge it. During discharge, energy is shunted from the cells with slightly higher capacity, to those with lower capacity, so that as the SoC approaches zero the cells are at similar voltages and ideally all hit the minimum of 2.5v simultaneously. During charge the reverse happens so the cells top out at the same time.

Yes a battery can suddenly die. Lead debris builds up at the bottom of the battery and eventually reaches the plates, where it shorts out. This takes a cell out and the other cells discharge through it. So probably just one battery is to blame, and you can possibly tell because it might be warm. But if the batteries are the same age, the other ones won’t be far behind and the best option is to replace the lot, and 7 years is a good life. It won’t be an unexpected heavy drain by something - if it were, the SoC meter would show a low SoC. But you said it still showed 99%.

I disagree, top balancing occurs when … the system is top balancing (by turning on the balancing resistors etc). I could drive my car, I have the keys in my pocket and the car is a few feet away and it has petrol. So I am in a state where I could drive it. But I am not driving it. Just as well as I’ve had a gin and tonic! There are two issues at play, the need to top balance and the need to charge to 100% ish to synchronise an Ah counting battery SoC meter. The latter is necessary reasonably frequently, every few weeks depending on how accurate you need the SoC indication to be. That is why the system is placed in a condition where the system COULD top balance. But it doesn’t, because it doesn’t need to. Jolly good. Jeez one cell at about 3.44v and one at 3.65v. And 1/2 a day to rebalance. That is terrible. How long since the last balance? Something is wrong with your system. Do you have some tap off part of the battery to run something at say 12v? If not I would be worried.

My evidence is based on my own data - that my cells don’t go out of balance. I did ask IanD several times for similar data ie how often/how much/if at all his cells go out of balance, but no response, just repeating the mantra. This leads me to believe that his cells don’t go out of balance either. It’s true that some manufacturers mention the need, but manufactures (who don’t actually make any cells) say lots of things, some of which are valid and some are not. As an example, some manufacturers’ literature thinks Peukert is important for Ah-counting SoC meters, others think it is not relevant. So in order to refute my supposition I’d need actual data, not something written by a manufacturer’s technical author, someone who has probably never used a Li battery and is writing out of an abundance of caution.

Seriously, I think one of the issues is the melting point of lead-tin solder, which is about 180C. An alternator can get quite hot in places and obviously one doesn’t want the solder to melt! I noticed that the Iskra regulator chip leads were spot welded, to avoid the risk of melting solder. Lead-free solder has a higher melting point and thus is preferable.

If only you had presented any data. Such a shame you didn’t. Long post, lots of opinion, no evidence. Same same. Although you are conflating balancing, with synchronising Ah-counting SoC meters. But then again, since you have said that your own SoC meter only drifts 1% a week, you did provide evidence that synchronising SoC meters is only required every several weeks. On which we agree😍

I was going to say kneet, but that might be inappropriate.

No. Carry on. And if there are complaints, reverse back and do it again. Although Caution, a nutter in a Dawncraft is probably faster than any narrowboat!

The reason why I do sometimes resort to criticising you personally, is because it is your habit to make long posts spouting a whole lot of stuff without presenting any actual evidence. And when presented with someone who has personal experience of an issue, you discount that and continue to spout the same imagined stuff and provide no supporting evidence. You think people should believe it just because you say it. And even when people do agree with you, you still crave arguing with them. This is unreasonable and irrational behaviour and I don’t have a method to deal with it other than making comments like “neuro diverse”. That surely is better than “fantasist liar” isn’t it?

The cheapo (at the time) cells I bought direct from china were very well packed.

You have presented no facts or evidence. You have only presented your opinion as if it were fact. I realise that in your world, your opinion IS fact. But not for the rest of us. Maybe it depends on exactly which model you have, but they mostly seem to have a link wire that allows remote turning on and off. The little green link wire bottom left in this pic: The two connections allow for various schemes for remote on/off: The slight problem being that you can’t connect the BMV relay to both the MPPT and the B2B, because they work at different voltage levels. So you would need another low power relay to operate them both, that relay being operated by the BMV relay.

Yes you could do that. But it makes it all rather manual and one day you will forget to turn it back on again and then wonder why the lights go out. Or lose your phone and be unable to turn it back on again. Humans are unreliable hence IMO it’s better to automate it. Funnily enough I seem to still be floating. As usual IanD made a statement that you sucked up as truth, without providing any evidence. I did look again for the research paper but couldn’t find it, so whether IanD’s recollection is accurate is unknown at this time. But since your bromance is firmly established, obviously you won’t be interested in the facts. 1. You have no evidence for this. I disagree. Although the harm is modest, it is still harm. 2. A better idea is to stop charging at a specified SoC 3. Obviously 4. You have no evidence for this. I do have a Fogstar battery in the caravan (4S configuration), last time I took it to 100% (several months after the previous time) balancing was not invoked. 5. Not a cogent comment. Do you mean that cell balancing is required routinely (I disagree). Or that you can only balance when very close to 100% (I agree). 6. Careless typo which renders the point indecipherable. But if you mean relay, then yes but another relay would be needed. 7. Easier for you. Not an issue for me. 8. Just remind us how many leisure lithium battery installations you have experience of?

Oh good, that means I won! But I know that you will still be reading! So read that you once again have failed to provide any evidence to back up your conjecture, and are using sulking as a vehicle to cover that up.

What you repeatedly wrote is that voltage differences at lower states of charge are no indication of being top balanced. I have agreed with you several times. I don't understand why you need to keep pretending that I disagree with you. It's rather weird. There is a second part to my earlier post now, addressing your conjecture.

I am left wondering what sort of neuro-divergence it is that causes you to continue to argue against me when I have repeatedly said that I agree with you. It is quite weird! I guess you just like to argue even when there is nothing to argue about. Whatever floats your boat I guess, and glad to be of service. This is conjecture, you again have provided no evidence except repetition of your conjecture. There are of course manufacturing differences in cells, and this results in minor variations in capacity. Which is why a battery needs its cells to be top balanced. However they will only go out of balance if there are variations in charge efficiency. They will not go out of top balance if there are variations in capacity. As we know Li cells have a very high charge efficiency, pretty close to 100%. And it is pretty hard to see how this can change because the current flowing across the electrodes arises only from the migration of the Li ions. There is no sneaky alternative path for current and Li ions don't suddenly disappear or appear. Unlike lead acid, where the conversion of water into O2 and H2 results in a lower and variable charge efficiency. As I said before, if a boater finds that their Li battery is in need of regular balancing, something is wrong. Repeated balancing just masks a developing problem. I know this because it is exactly what happened to me. One thing you haven't shown us in all your swathes of data, is just how much and how often your own cells need balancing and by how many Ah. I suspect you will find that the answer is, they don't. Please show actual data, not just repeats of your mantra.

Please provide this overwhelming evidence. Otherwise everyone will (correctly) think you are making it up. Well, to be more precise, I’m sure Li cells do eventually go out of balance as they age differentially, and since you haven’t defined what you mean by “a period of time” your comment has no actual meaning.

Even though everyone on here knows you have intimate knowledge of these systems since you designed them all, perhaps you could provide evidence from all those battery manufacturers who say out that their Li batteries seem to go out balance quite quickly and need to be balanced every couple of weeks? Rather than just saying it and thus hoping that makes it true? No I thought not.

Perhaps you could mention the people on here who find their Li batteries need routine balancing? I can’t think of any. But of course you should introduce us to your imaginary friends, it’s only polite. If you took your thumb off the transmit button and read what I wrote instead of imagining what I might have written, you would notice that I agreed with you that cell voltage mismatch (or match) at anything less than very close to maximum cell voltage (3.6 or 3.65v) is meaningless. The only relevant thing is that all the cells approach 3.65v at very much the same time with minimal difference. But once this is set up, a decent system will not need much further attention. If a series string of Li cells is routinely going out of balance, something is wrong even if you are in denial.

It’s actually quite interesting because the basic physics is about rate of change of magnetic field creating a VOLTAGE, not a current. And in order for anything to happen, the voltage swing on the stator has to exceed the battery voltage plus 2x diode voltage drop before ANY current can flow out of the alternator. So even with zero output, it still needs perhaps more field current than you might think to make the stator voltage swing up to the 12.7v + 0.7v + 0.7v (zero output, but keeping the W terminal working). I’d need to check again but I think my system shows about 0.25A field current for zero output, (eg when it drops into float mode and residual battery voltage is higher than regulated voltage) out of a maximum of 4A for full output. ie the first 6% or so of field current doesn’t produce any output, it just keeps the W terminal etc ticking over. So I can see no excuse for an alternator going over-voltage under no load, unless there is a fault. But surely on most boats with dual alternators (and there are a lot of those these days) the starter alternator is not supplying any significant current several hours after start. Ok perhaps there is a very small current to run the gauges on the panel, but this can’t be much, and some boats don’t have gauges. In OP’s case the high voltage seems to occur pretty much straight away, when the battery is surely taking a bit of current. So I would either suspect a fault somewhere, or as you say a regulator that is set rather high.

Then the regulator should shut the field current down to near zero and regulate the voltage at the specified value. This can cause a 9 diode machine to glow the warning light and/or lose the W signal, but it doesn’t cause an over-voltage in a correctly functioning alternator.

Everyone on here who has experience of Li batteries says they don’t go out of balance, except you. Perhaps your system is not as fabulous as you hope, and there is some defect that is causing the problem? It seems hard to believe that cell imbalance occurs randomly amongst the cells, I would be fairly confident that it was always the same bank of cells that gets low or high, compared to the others. This would point to some defect in the cells or wiring - you might remember that I had a problem with cells suddenly seeming to go out of balance, it was a bad internal connection in one of the cells that I was able to remedy. So I my experience, cells going out of balance is an indication that something is not quite right.

I don’t understand why you say this. The alternator is connected to a battery, which sometimes has a load on it but other times doesn’t. I can’t see any difference between that and a starter battery which initially is slightly discharged from starting, but after several hours of running is fully charged and not taking any current (or any more current than OP’s buffer battery). A correctly functioning alternator should not allow the voltage to rise above the regulated voltage just because the load is very slight.

Surprisingly, in this case I have to agree with IanD. In my setup, during the late stages of charging, a certain cell might be at a higher voltage than other cells. But towards the end of the process as the voltages approach 3.6v, a different cell will sprint forwards and become the highest cell. Don’t ask me why this happens but it definitely does. So the highest cell at say 3.45v will almost certainly not be the highest cell at 3.6v, and the aim of balancing is so that the cells are all at equal voltage at 3.6 or 3.65v where it matters, not at some lower voltage where it doesn’t matter.