nicknorman

The large volume of air is in part to assist in cooling of the "important bits" ie the actual contacts and conductors. Everything has some resistance and when current flows, that creates heat. Heating of the conductors is the primary constraints that limits the current rating. The heat has to be disspated or the temperature rises without limit and things melt (and go on fire!). The heat dissipation to the outside world is aproximately proportional to the surface area of the containing thing. Make the enclosure just big enough to hold the contacts, and you either have to derate the switch or increase the amount expensive materials (copper etc). It is easier and cheaper to increase the amount of plastic and air. And it makes it easier for gorilla-fingered numpty boaters to grasp and turn. I suppose the only thing is that if the negative conductor is connected to hull via the boat's dc system, the postive end remains at high voltage relative to hull and touching the wiring coming into the switch or around the panels could be fatal. Whereas with double pole, the voltage is "floating" and touching any one conductor has no effect.

Yes this was the thrust of the video. But plenty of switches are dual rated ie for both dc and ac, and thus there is only one switch speed. But of course the dc rating will be less than the ac rating. But all this is only about what happens when you open the switch whilst current is flowing. If you don’t open the switch, the propensity for overheating and thus fire risk is not dependant on ac vs dc.

The arcing on the DC only arises due to inductance in the circuit. The heater in the video has a lot of coiled wire inside which I guess gives it plenty of inductance. I don’t know what the inductance of a solar panel itself is, not much I’d have thought. And the wiring is in straightish lines so again very little inductance. So I think the video rather over-eggs the issue as applicable to solar panels. Whilst of course it’s true that a switch rated for ac will have a different (much lower) current rating for dc, that is only an issue when interrupting a high current with significant inductance in the circuit. It has no bearing on the current rating whilst the switch is on. And if you only switch it off when the current is low (batteries fully charged, darkish etc) then again no problem. So yes of course the correct answer is to ensure that the dc rating of the switch is adequate, but in practice let’s not over scare-monger!

Not necessarily, only in terms of the application and hence the pressurisation. If they are adjacent to each other, one will be connected to pipework that gets hot when you run the hot tap (the expansion vessel), the other will be attached to pipework that remains cold (the accumulator).

It’s all a bit silly really. Gas work can be done by anyone on a leisure boat. Then some time later, the owners decide to live on the boat. So the previous “uncertified” work remains unexamined by a GS person (until the next BSS) in 3 years time or whatever). And how long g do you have to reside on the boat for it to become residential? A night? A week? A month? A year? Who knows.

However they only detect mains voltage relative to earth. So they cannot be used to check for continuity in the neutral wires. And won't work unless the inverter is NE bonded and the boat hull is bonded to earth (which it should be of course).

I think you will just have to check for mains voltage along the system, starting with the plug. Presumably you have checked that the plug fuse is OK? If it were me I’d plug it into the inverter with its lid off (as shown) and use a multimeter set to ac voltage to check for 230v between live and neutral. If not present, it’s an issue with the inverter. If present, move to the distribution panel and check for voltage on the inverter input wires (right of the picture) etc. Of course, mains voltage can be fatal,so you need to be very careful when doing this. Id also mention that, whilst it’s probably not the issue, it is bad practice to have screw down connectors onto stranded wire. You can see that some of the wires going into the chocolate block connector have ferrules, but others are just bare wires. The screws tend to cut the strands and make a poor connection and potentially cut through the strands. I’d get a packet of appropriately sized terminal ferrules. It wasn’t.

On the essential maintenance thing, I disagree that blacking is essential maintenance and anyway, have we even confirmed that “essential maintenance” on a house is something that benefits will pay for? As MtB pointed out, my comparison with a rented house and window frame painting was not valid because the landlord is responsible. But one can own a house (just as one can own a boat) and end up on benefits, let’s say after the mortgage has been paid off. Is there any confirmation that the benefits system will pay for essential maintenance for a private residence, and if so what is the definition of “essential maintenance” in the context of the benefit system? I have never heard of such things being paid for by the benefits system, but perhaps I have just missed it?

You can’t, because it is insignificant. But you knew that!

I would relate it to the mainstream, ie housing. You can get assistance to pay rent via the benefits system. This translates into the benefits system paying mooring and CRT fees since this is a direct equivalent of rent. Renting the mooring and renting the water on which to float the boat. But I would think it highly unlikely that the benefits system would pay for blacking. The equivalent would be the benefits system paying to have your house’s wooden window frames painted. Maintenance, yes. Essential maintenance, no. The boat will carry on floating for decades without the blacking being redone, just as the windows will survive decades of not being well painted.

Yes it's chipboard. Chipboard is fine as long as it doesn't get wet. However on a boat, the chances are that it will get wet at some point, or at least damp. So it will swell up and fall to bits. It may be cheap and it may last a while, but eventually you will have to redo the work.

I like real ale, but on a hot summer’s day, sometimes a cold Peroni is better!

Or you could simply use a BMV712 as I suggested earlier, total cost around £95. Or free if he already has one.

It is a Vintage Inn, so the food is quite OK but a bit pricy. Probably more than you were prepared to pay, but the OP is on holiday so no expense spared!

The problem is that I do know better than you.

Well I guess you should know, after all you did design the human brain.

It depends on your priorities for pretty vs good pub! But perhaps Coven would be a good idea since there is a canalside pub there, and good mooring just before it (although not great views due to the trees). Anchor Inn, Cross Green, just on the outskirts of Coven.

I tailored my answer to the questioner, as any good answerer would do. MtB is not stupid, he is quite clever at mending boilers and I think he would have no problem with charging to 100% once a month. 1% a week doesn't present a huge problem, that would be 4% after a month, or stretch it to 8% after 2 months. Not a particularly onerous situation. And if the error drift was negative, then eventually the battery would reach 100% whilst the indicated SoC was say 90%, which would then reset the BMV automatically. So it is only potentially a latent problem if the drift is positive. One can reset the zero on the BMV712 and probably this can be used to reduce the error below 1%/week.

The question was "is there an easy way to ...". Obviously a system that takes into account voltage AND charging current etc is a good way to do it. However it is not easy (or cheap) to install as a DIY project. Whereas using a BMV712 to control charge termination based on SoC, is. We are not talking about my boat's system, or your boat's system. We are talking about a simple way to avoid fully charging a Li battery from solar every day.

I disagree. It is hard to use voltage as the trigger to terminate charging since the voltage vs SoC relationship is very flat over the relevant range, and the voltage vs charge rate is relatively steep. So if you set decide to terminate solar charging at 13.5v (which is far too low IMO) and there is strong sunlight (= fast charging) then the 13.5v will be reached early at a low SoC. If on the other hand it is overcast (= slow charging) then the SoC at which the terminating charge will be reached will be much higher. You can set the BMV712 to terminate solar charging at the specified voltage, but it doesn't work for the reasons explained and is thus the wrong way to do it. Using SoC is the correct way to do it, albeit one does have to fully charge every couple of weeks / a month or so to reset the BMV to 100%. This can be accomplished by changing a setting in the solar, disabling the relay in the BMV or adding a switch into the cable to manually force full charging. And 80% is a very low terminating SoC, something more like 90% or a bit more is better, and still avoids high cell voltages (cells going "up the knee") when charging at typical narrowboat rates.

But then you are well known for your shy and retiring public face. But then she is a barely-moving liveaboard, so the solar makes perfect sense in the world of compromises. Although I would comment on the wasteful carbon footprint of her henna hair dye and pointless steel bits in her face. All gone now in the days of Lithium, where the aim is to NOT leave your boat with fully charged batteries.

A fairly easy way to control Victron solar charging to terminate at a specified SoC is to use the BMV712 relay function and a lead plugged into the VE.Direct port of the solar. If you have a BMV712 that is!

In part it depends on whether you have any sense of aesthetics. If you don’t care that your boat looks ugly due to loads of solar cluttering up the roof, then fine. We do care though, so we don’t have any. Just because you don’t care about the aesthetics doesn’t mean you should try to force your opinion on people who do, and vice versa.

Presumably during this 3 mile talk you are alone? Otherwise any companion is going to have to feign deafness. A lot of boats on the towpath have solar. This is because they mostly use the canals as a place to live and don’t want to move much. A bit of a clue is that they are moored during your 3 mile talk, not chugging along. Unless you are accustomed to talking for 3 miles at night? A boat set up for cruising is a different kettle of fish. We don’t have any solar because we move every day or at least every couple of days. Solar is ugly and a nuisance so only of merit if the boat usage justifies it.

Your proposal is fine. No problem to connect 2 alternators to one battery, and use a B2B (or two) to charge the Li. Have the B2B operation controlled by the ignition switch.