IanD

There's very little that one hydro station connected to the grid can do though, the mains frequency error is controlled by the central grid control turning power generation/pumped storage up and down nationwide. Depending on load the accumulated error before the corrections catch up is routinely up to several tens of seconds, and is worst in periods of heavy power use in winter when it could be over a minute -- here's some data from one month in summer 2012, which was before much renewable energy was around so more rotational inertia than today... 😉 https://www.electric-clocks.co.uk/Technical/synchronouselect.html

Or people in urban areas moving in next to a pub -- that's been there since long before they were born -- and complaining about the noise or people outside. Hey, did you ever wonder why that house you snapped up was a bit of a bargain? 😉

A non-apocryphal story -- because I was there when it happened! -- was in the heavy Electrical Engineering lab at Cambridge, where there was a massive (3-phase?) motor-generator pair reputed to have come out of a submarine (this *may* have been apocryphal...). One of the experiments was to do an efficiency test, the motor was driven off the incoming mains and the generator dumped its power back into the mains, which only had to supply the difference -- IIRC each was rated at several MW, but the difference (loss) was only a few tens of kW, the whole thing had to be run up and synchronised very carefully according to the experiment instruction sheet. I was working on another experiment in the lab when the bright sparks running the motor-generator experiment had a brainwave -- what happens if we switch the generator phase over while it's running? The answer is that it instantaneously tries to take getting on for 10MW out of the mains, which shuts down not just the lab or the building but the whole of West Cambridge... 😞 At which point Bill -- the guy who ran the lab -- comes running in screaming "Which one of you stupid c*nts flipped the motor-generator phase?"

Sorry Nick but I'm going to disagree here -- assuming all the waveforms are sinewaves and the load is resistive, all the voltages and currents are in phase with each other. If they weren't you'd just get reactive currents flowing from one to the other, for example between inverter and incoming mains, which just increases losses but does nothing to frequency since the mains is effectively immovable. It's definitely *not* about "pushing the phase", this is something you absolutely do not want in this application. Nothing is zero impedance, either mains source or inverter output, so the currents flowing from each depend on the source impedance and the open-circuit voltages of each. If the load draws no current and both mains and inverter are the same (open-circuit) voltage no current will flow when you connect them together, but when you draw a load current it will split between the two according to their source impedances -- for example if the inverter impedance is double the mains it will only provide one third of the current, not half (or vice versa). To change this (e.g. more current from inverter to share equally) the inverter has to change the open-circuit voltage it generates, for example by increasing it slightly (Kirchoffs and Ohms Laws). It *doesn't* change or lull phase to do this, unless impedances are reactive -- which they probably will be, but that's a different kettle of fish... This is why it's so difficult to get a system like this working, because the currents flowing depend not just on the voltages but also source and load impedances -- and these are also unlikely to be resistive (including shoreline and battery, when cabling is included) so phase shift comes into it too. The inverter has to continuously measure the magnitude and phase angle of the current it's providing as well as the magnitude of the incoming voltage, and change the amplitude and phase of the waveform it generates internally to provide the required amount of current -- usually while also trying to minimise reactive power (keeping output current in phase with output voltage) since this increases inverter losses.

Clockwise like most alternators, the cooling fan pulls air out of the casing. (the alternator itself will work either way)

All modern routers do channel aggregation, the newer/more expensive ones tend to aggregate more channels and across multiple bands. This tends to only help in good reception conditions where you're near enough to a mast to pick up multiple channels (especially in the higher frequency bands with more bandwidth) and get very high data rates as a result, not that important for most boaters.

Which IIRC was also what the organiser said would be done when the appeal for help was made, so anything else could be objected to on the principle it wasn't the conditions under which people donated. Maybe nobody thought such a big sum would be collected, but that's just a bit of good luck for the three boaters concerned -- nobody gave their ten quid (or whatever) on the condition that "if they do too well out of this I want some money back"... 😉

Exactly -- in this case "pushing harder" means trying to generate a slightly higher voltage than the other one, or pushing in more current. What it *isn't* doing is trying to push the phase forward (which *is* what you said...), this is what power-station generators do to try and push the grid frequency back up if it drops (by effectively adding reactive power), but good luck trying to do that with an inverter... 😉 Either way it all looks a bit like magic viewed from the outside, and even on the inside the control algorithms needed to make this work reliably are pretty complicated, especially with different grid (or even more so generator) and load conditions -- Victron seem to make it work pretty well, others not so much or don't even try.

Maybe not, mine is leisure use only -- but then how many sofabeds *are* built for continual every-day use?

What Nick said isn't correct either -- if the "power assist" generated the same AC voltage but with a leading phase the current would be maximum near the zero-crossings (biggest voltage difference) and minimum near the peaks (smallest voltage difference). What it actually does is to try generate the same voltage and phase as the incoming mains but also dump in-phase current into the load to generate power. But it won't close the relay which connects the inverter to the output until the waveform it's generating closely matches the input waveform (frequency, phase and amplitude). Once this is done it continually monitors both voltage and current -- input and output current -- and dumps enough current in to stop the shoreline current exceeding the limit that is set. For example if the shoreline limit is set to 16A and the load demands 25A, the inverter will add 9A boost current (by discharging the batteries). If the load them drops to 16A or below the inverter will stop doing power assist.

That's not how an RCD works, it sees the difference between the current into L through the load and back through N, and this current only flows when both contacts are closed, so it shouldn't matter which one closes first. The exception is if there are some capacitors*** somewhere between N and E (e.g. in a noise filter -- or even in the RCD?) which normally don't see any significant voltage, if the L contact closes before N (so the full mains voltage appears on N) then a current spike could flow into L then through the capacitors and back through E instead of N, which could trip the RCD. RCDs aren't really intended/designed to be used with supplies that are switched at the input side, they're intended to sit between a live supply and loads at the output. Doing a switchover with everything off might help, or it might still trip when you turn things back on -- in which case replacing it might help, or might not... 😉 *** I've seen this done deliberately as a "safety feature" so that an RCD will trip if L and N are accidentally swapped over.

Looks similar to mine (2 x 2-seaters linked). I'd recommend the (admittedly more expensive) pocket-sprung versions/option, they're very comfortable both as a sofa and a bed.