nicknorman

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.

Yes perhaps it’s to do with energy throughput rather than instantaneous power. But your mention of 0.25% per 100% DoD which sounds a lot. We do cook with electricity mostly these days - air fryer, electric kettle, toaster, electric blanket on all night in winter - and sometimes can gobble up 1/3 capacity (ie 200 Ah) per 24hrs, may be 1/2 capacity (300Ah) in winter. But as I said, when I do a full charge to reset the BMV, the charge voltage is 14.3 ie nominally 3.55v/cell and the balancing algorithm would kick in if any one cell reached 3.6v. But it never does, well not in several years. As you know, the difference in charge between 3.55v and 3.6v is miniscule. Whereas your 0.25% per full cycle would be 1.5Ah. Which is a lot. So I continue to maintain that a decent Li battery used for domestic purposes in a narrowboat, virtually never goes even slightly out of balance over several years of use. And anyway with my system, even if there is an imbalance that triggers the balancing circuit, there is no need to hold the cell voltages high, it works out a nominal amount to remove from each of the 3 higher cells and does that regardless of the charging having stopped.

IanD has electric propulsion. I guess it’s possible that the very high currents involved might be more inclined to produce cell imbalance, although I can’t immediately see why. There is no point in having a 4 top balanced a year routine if the cells are already in balance. Regarding the SoC drift, an Ah counting device has 2 main types of error: scaling error and zero offset error. Scaling error tends to not matter much because you take out and put in pretty much the same amount of charge. It is zero offset error that tends to cause a slow loss of accuracy of measured SoC, and this is not related to number of cycles. Also devices like the BMV712 have by default quite a big “ignore zone” where any low value currents within this zone are ignored. I think the default is 20mA or some such. But there are things on boats that consume less than 20mA but can be “on” all the time, and thus create cumulative errors. Which is why I have my “ignore zone” set to zero.

It is quite feasible to remote control the Orion B2B using the BMV712, but it would probably require an additional relay. The remote on off wire would be “armed” by turning on the ignition, but the relay could interrupt this so the B2B remained off or was turned off when the SoC exceeded the desired threshold.

You are in permanent transmit mode. Maybe check out your PTT button. It’s stopping you from receiving anything. As I said repeatedly there is no need for “routine top balancing”. I think our last top balance was at least a year ago, probably 2. When I do a full charge at 14.3v (3.575v / cell) the balance algorithm will be triggered if any cell reaches 3.6v. But they don’t. So no balancing. The 600Ah battery is top balanced within a very small margin, less than 0.5Ah which is inconsequential. The OP did already mention that he takes the batteries up to fully charged from time to time, to sync the BMV.

Hard to say from afar but I think the Wakespeed can do positive or negative field regulation, ie the other brush connected either to B+ or to ground. Does the configuration match the wiring? Edit, looks like there are 2 different wiring harnesses according to whether the other brush is connected to + or - Oh and have you connected the stator ac tap wire to eg the W connection on the alternator? Without it the Wakespeed won’t realise that the alternator is spinning.

No there was no mention or implication of not having a BMS. It is simply that the BMS only top balances the cells if they (or at least one cell) are charged fully. And in the case of shitty BMSs, held fully charged for a while.

Do try to keep up! This is why he has a BMV712 that turns the solar off at some specified SoC

No I can’t remember exactly, but it was quite significant. Of course the research only split the discharge into quarters. I suspect, but can’t prove, that the same differential would occur between cycling 45% - 95% vs 50% - 100%. ie it is just the very last bit that accrues the accelerated damage. The OP’s issue was with the exploding LA battery and it is the possibility of a repeat of that due to high alternator voltage that is his current issue.

Not really. The BMS monitors individual cell voltages and won’t allow any one cell to get over-charged. No 14.4v is fine if you want to fully charge a LiFePO4 battery. As long as you stop charging when the current has subsided to about 5% capacity.

Some confusion here I think! Firstly, it is not just about leaving the batteries at a high state of charge for long periods. Research has shown that cycling a Li battery between say 50% and 100% gives significantly shorter life than doing same between 25% and 75%. It is true that even with the former, the cycle life is long, but surely it is better to maximise the cycle life if you can? Secondly, the only point of top balancing is to be able to fully charge all the cells at the same time, in order to maximise usable capacity. If you never need to fully charge the battery, there is no need to have it top balanced. There is no “degradation” caused by not having the cells top balanced, other than an earlier tripping of the BMS shutoff if/when the user decides to fully charge. And at that point the issue is self-rectifying. I would imagine that the OP will be fully charging the battery in mid winter, but in the meantime it’s better to not repeatedly charge to 100% when the capacity is not needed (due to the abundance of solar). If you had any actual experience of Li batteries you would know that the whole balancing thing is a bit of a damp squib and nothing to get excited about.

There is lithium compatible and then there is lithium compatible. If you want the B2B to fully charge the lithium each time, that is easy. But not best for the Li if it’s not necessary (ie you don’t need all the capacity before the next charge). If you want to charge to a reasonably high but not full SoC, say 90%, then it is very difficult to do satisfactorily just by eg reducing the charge voltage. That results in a very slow and drawn out approach to the desired SoC, nullifying one of the main advantages of Li. What one needs to do is charge at a reasonably high voltage and then stop charge at the desired SoC. B2Bs generally can’t do that because they don’t know the battery SoC.

No. It’s no different from switching off any other load while the generator is running. There might be a bit of mains voltage surge but the genny electronics have to be designed to deal with a heavy load being switched off as this is a totally normal and foreseeable event, unlike for an alternator.

I would question whether the pair are not pleasure craft. Just because you are a licensed waterways trader in a historic boat doesn’t mean it is not a pleasure craft and such craft have no priority over non-trading pleasure craft. I seem to recall that the waterways trading licence specifically says it doesn’t bestow any right of priority. Agreed about the towing vs not towing though. Although really what this says is that when I am towing, I am not really under control and everyone else has to get out of my way. What happens when two towing pairs meet each other on a bend?

It is marginally better to take the positive and negative feeds from opposite diagonals of the pair due to the very slight resistance of the interconnecting wires, but in reality IMO it doesn't make any practicable difference provided the interconnects are reasonably beefy.

We’ve been up the locks (“the crow”) and along to the start of the pools with no problems a few times over the years. We didn’t venture very far into the pools though, just enough to turn round. And we draw 2’8”. If you like exploring the backwaters, there’s no reason not to.

The BMV712 resets to 100% when the specified conditions are met ie the voltage is above x, whilst the current has fallen below y, and this lasts for z minutes. By default out of the box, y is 4% of capacity which in your case is 20A which in my opinion is too much, so the BMV resets to 100% rather early. The scaling on the graph is a bit hard to read, but I’d check the tail current parameter and if still set to 4% I’d change it to something like 1.5%. But ultimately I suspect it is more an issue of lead acid losing capacity. Lead acid is intrinsically utterly crap! Lost capacity might be restored by an equalisation charge ie around 15v for an hour or so, if you can make it do that. And presumably the electrolyte level is Ok?

Most dc dc chargers have some sort of remote on-off input so you just need a low current control switch, rather than a fat isolator switch in the main feed. You can also automate it via the relay on something like a BMV712 that is measuring the Li SoC. If I were doing it I’d probably have a switch to select between BMV712 automatic control, and “always on” to allow synchronising the BMV to 100%. Or a 3 way switch with an “always off” position too.

I think the drawing is unconventional in that the devices are shown across the wires as opposed to in series, but I think the principle is ok. You have shown 15A fuses in the diagram but 150A fuses in the text. The fuse rating should relate to the cable used, so 150A will be fine if the cable is quite thick and rated for that current. I would have thought 250A for the bow thruster was not enough, but it depends on the bow thruster!

A lifepo4 battery probably can’t run a bow thruster as it (probably) can’t supply enough current due to the limitations of the BMS.

No. 14.7v is not that high. But there might be a problem with a field diode. It might go higher under no load so best to sort it and even 14.7v for long periods is inadvisable. Voltage decreasing at higher revs might also pint to a field diode. I think.

The Sterling reg can only increase charging voltage, it can’t decrease the voltage below whatever the alternator’s internal regulator sets.

Best is when 2 boats are coming out of one lock in parallel and 2 boats coming out of the other lock in parallel. One pair holds centre ground and the other pair splits to pass the together pair, before rejoining each other before entering the lock. ’tis a thing of grace and beauty to behold. And what could possibly go wrong?

When sharing wide locks, the correct way is for both boats to enter simultaneously and then there is no need to worry about staying against the side. Unfortunately lots of people seem unable or at least unwilling to do that.

We have certainly encountered single handers who are reasonably expeditious but the only time they don’t hold us up is if every lock is in their favour and of course not in our favour. Single handers having to set ahead has got to be a lot slower than 2 people doing same. I recall having to wait for a single hander to go through a lock on the Avon, it was quite a long boat that had to go diagonal so we couldn’t share. We offered to help but this was strongly rebuffed. I am not kidding (because I timed it) but there was 15 minutes between the top gates being opened and the bottom paddles being raised, the time being spent faffing around with ropes and micro-positioning the boat. We then whizzed through and overtook him in the next reach, taking the time to hand him the windlass “en passant” that he had left lock-side.