Sverige
A Brit in Sweden
I have a three core cable which runs the length of the outside of my house, from the south facing location where my off grid solar panels are to the north side of the house where my charge controllers and battery are housed. This cable is already in use, carrying mains voltage (230V AC) live, neutral and earth from a supply on the north side to a circuit of outdoor lighting on south side which operates from dusk until dawn.
I have the idea that I could maybe use this cable from dawn until dusk to carry low voltage in the opposite direction, from my solar panels to my charge controllers. Then switch back at dusk to the nighttime use, carrying mains to the outdoor lighting. This has the advantage that I don’t have to install another cable on the outside of my house. Cable is expensive right now!
To do this safely requires me to ensure that the mains supply can only be connected to the north end of the cable if the switching at other end of the cable is definitely connected to the outdoor lighting circuit, ie never when the solar panels are still connected at the south end.
So I need an interlocked switching setup, where the switching device at one end can only operate if the other switch has already done so. I have a pair of Sonoff 4ch Pro relay sets available, and each contains 4 changeover relays with sufficient current rating, so in principle I could just connect one at each end of the cable, with the three cores of my cable connected to the common poles of the relays (relays 1, 2 &3 in each sonoff), then have the low voltage connections (solar panels & charge controller) connected to the NC terminals, and the mains supply and destination circuits connected to the NO terminals. What stops the north end switching before it is safe to do so? There are a few options, some of which make use of the Sonoff software functionality, but I prefer to use the third core of the cable to transmit low voltage power (12V) from the south relay set to the north side, and to use this power supply to power the relay set there.
With this arrangement the relay set on the north side cannot switch mains power into the cable unless the south side has already switched over to connect the mains load devices. Control of switching at the correct times of day is easily handled within the sonoff software, which will take account of changes in the length of daylight, DST time adjustments, etc.
Have I missed anything? Is there a better way? Just about the only way I think this could fail is if the relays on the north side remain connected to their NO poles in the absence of power. I know this can happen rarely with relays due to magnetisation of the contacts, usually from excess currents. I’m not sure how worried I should be about that, but presumably as a ”belt and braces“ safety measure an inline fuse can protect my solar panels as even the briefest mains voltage would cause current way above the “normal“ 10A the panels supply.
I have the idea that I could maybe use this cable from dawn until dusk to carry low voltage in the opposite direction, from my solar panels to my charge controllers. Then switch back at dusk to the nighttime use, carrying mains to the outdoor lighting. This has the advantage that I don’t have to install another cable on the outside of my house. Cable is expensive right now!
To do this safely requires me to ensure that the mains supply can only be connected to the north end of the cable if the switching at other end of the cable is definitely connected to the outdoor lighting circuit, ie never when the solar panels are still connected at the south end.
So I need an interlocked switching setup, where the switching device at one end can only operate if the other switch has already done so. I have a pair of Sonoff 4ch Pro relay sets available, and each contains 4 changeover relays with sufficient current rating, so in principle I could just connect one at each end of the cable, with the three cores of my cable connected to the common poles of the relays (relays 1, 2 &3 in each sonoff), then have the low voltage connections (solar panels & charge controller) connected to the NC terminals, and the mains supply and destination circuits connected to the NO terminals. What stops the north end switching before it is safe to do so? There are a few options, some of which make use of the Sonoff software functionality, but I prefer to use the third core of the cable to transmit low voltage power (12V) from the south relay set to the north side, and to use this power supply to power the relay set there.
With this arrangement the relay set on the north side cannot switch mains power into the cable unless the south side has already switched over to connect the mains load devices. Control of switching at the correct times of day is easily handled within the sonoff software, which will take account of changes in the length of daylight, DST time adjustments, etc.
Have I missed anything? Is there a better way? Just about the only way I think this could fail is if the relays on the north side remain connected to their NO poles in the absence of power. I know this can happen rarely with relays due to magnetisation of the contacts, usually from excess currents. I’m not sure how worried I should be about that, but presumably as a ”belt and braces“ safety measure an inline fuse can protect my solar panels as even the briefest mains voltage would cause current way above the “normal“ 10A the panels supply.
