nicknorman

I think you might struggle to install it low enough so that shower water reaches the manifold by gravity in order to activate the pump. Most shower waste outlets are virtually on the baseplate. And if it fails, sink water may flood the bathroom.

Yes I am not clear about this and it is a bit late to get my head around it but anyway I see I mis-wrote. What was actually written was degC/min-Ah. I'll edit my earlier cockup. But that little detail aside (!) my point was about the differences between LFP and the more energy-dense chemistries, around a factor of 100.

I've recently gained access to British Standards online, giving me access to the latest version of "small craft - lithium-ion batteries. Most of it is pretty sensible and I am compliant eg with things like "Charging sources shall be operated/controlled to meet the charging profile recommendations provided by the lithium-ion battery or cell manufacturer." which I would take to mean that relying on the BMS cutoff to ensure safe charging, is not acceptable. But relevant to the discussion about battery abuse, the BS makes reference to a paper "Investigating the Role of Energy Density in Thermal Runaway of Lithium-Ion Batteries with Accelerating Rate Calorimetry" which is freely available on line. There is a graph of thermal runaways with different chemistries. First of all it is interesting that thermal runaway only really "takes off" when the temperature gets over 200C (or 180 for LiCoO2). Which is quite hot. But once thermal runaway is in full swing, LiFePO4 suffers a rate of (adiabatic) temperature rise of around 2 or 3 degC per minute-amphour. Whereas the likes of LiCoO2 is around 400 and NMC around 170. So there is a massive difference between the rate of energy released by LiFePO4 vs these other chemistries. I know that we knew that, but it's good to see the hard data.

What very different outcome do you envisage? For a LiFePO4 battery it would have been a much better outcome- the BMS would have isolated the battery with no damage occurring. This is the thing with Li batteries, there are two levels of protection, the charger’s regulation AND the BMS. With lead acid there is only one. But even with the double failure of charge regulation and BMS, chances are the LiFePO4 battery would have suffered a similar fate to the LA - been badly damaged. But not gone on fire nor risked spraying boiling sulphuric acid around.

Oh dear! Can’t say I’m too surprised though.

So no actual data or evidence, just hearsay and someone’s opinion.

I would strongly recommend reviewing the BSS inspection criteria before starting. https://www.boatsafetyscheme.org/media/299451/bss-complete-ecps-private-boat-public-version-2023.pdf For example the boatyard is quite correct, the starter must go through the engine battery isolator ditto the alternator. It is not that one needs to isolate the battery from the engine, it is the other way round ie isolate the engine electrics from the battery (source of a lot of energy). If someone is working on the engine they don’t want an accidental touch of eg a spanner on the starter stud and the engine casing, to short circuit the battery, melt the spanner and spray molten metal in their eyes. If you just rewire it your way, it may fail the next BSS check and you would have to redo it. Most boats have 2 isolator switches, one for the domestic and one for the engine batteries.

Interesting. It’s hard to think of a reason why a boat would sink that didn’t involve some negligence of the owner. Perhaps this is why boat insurance is so cheap!

Surely it is mandatory to have 3rd party insurance to get a CRT licence?

Yes but the REALLY KEY POINT is that the cars have a completely different and more volatile battery chemistry. Yes they are checked, but there are still fires…

But how many boats have gone on fire due to their LiFePO4 batteries catching fire spontaneously? Vs how many have gone on fire from solid fuel stove installations, curtains over gas stoves, gas leaks, petrol fumes etc?

There are a few possible different technologies for flame failure detection, one is a thermocouple that gets heated, a small voltage is produced that keeps the gas valve open. It takes a few seconds for the thing to be heated enough. If the flame isn’t really playing on the probe, or the probe is generally “tired” then it can be slow or malfunction. As mentioned, if the flame isn’t playing on the probe this is usually because something is upsetting the flow of gas and/or air. Dirt or corrosion in the jet and burner. Another technology is a flame conductivity check - an electrode is bathed in the flame which also reaches the metal of the burner. The flame is a plasma which is highly conductive and the system detects low resistance and keeps the gas valve open. This type of system needs a power supply (battery or supply from the boat) , whereas the first I mentioned doesn’t. The latter generally uses the sparking (lighting) electrode as the flame probe, and the flame shape is more critical than the thermocouple as the flame has to touch both the electrode and the burner metal. But again, dirt and corrosion in the jet and burner are usually at the root of the problem.

You can lock up from the river to Stourport basin using either the wide locks or the narrow ones. They are in parallel. Narrowboats should use the narrow locks to save water. But the Staffs and Worc after Stourport basin is narrow only so you can’t go beyond the basin.

No I didn’t. The IR is very small and I can’t see that there’s much variation. Probably more variation in the interconnect / connection resistances. And also IR is made up of at least a couple of things, one being the ohmic resistance and the other being the “chemical resistance” ie the reaction rate. Even if the former is fairly static, the latter won’t be - varying with temperature, and non-linearly with load. Possibly it might be relevant if one was operating the cells at 1C rates or higher, but the max I get to is about 0.35C and that only for short periods (electric kettle), so I can’t see that slight variations in IR are going to be consequential.

At a loose end on the boat today in the marina so I thought I’d take the battery up to 100% again to see how the balancing is. And also to demonstrate that balancing is only appropriate right at the top. The following pics taken of the BMS display during the very late stage of charging. In the first pic you can see the cell voltage order is 1,2,3,4 And so you might think that cell 4 needs a bit taking out of it. Also of note is that the battery is now 99.7% SoC and yet the voltage is not that high yet - see other screens from BMS.The last bit of voltage gives very little extra charge… But right at the end, the cell voltage order is quite different at 4,2,3,1. So the lowest cell from before is now the highest, and vice versa. So if anything cell 1 needs a bit taking out, although the split of 11mV is below my threshold for activating balancing.