Bit of background: I have PV arrays on the NE and NW elevations of my roof (live in the southern hemisphere). The NE also has a solar thermal HW system. Feed in tariffs are punitive, so I try to shift as much consumption to periods of high solar yield.
I wrote and fine-tuned some python code which establishes at midday each day how long it feels it should run the immersion heater based primarily upon the insolation of the NE PV array until that point, but also considering season, ambient temperature and forecast (these values are all scraped from the web rather than measured locally.
The way in which this controls the immersion heater is by way of an SSR, which remarkably (to me) was able to energise from just the 3.3v logic level signal from the RPi GPIO. It has worked well for ~8yrs, but yesterday we had cold water.
Testing the system from bottom to top, the RPi is up and responsive. It's giving up 3.3v on it's GPIO on demand, and this is readable at the SSR in the roof. Switching the GPIO in software gives rise to 240vac reaching the thermostat, and that in turn gives up 240vac to the element terminals when water temp is below the setting of the thermostat, typically about 60 celcius.
The thing is, the way in which I have established if the element is in operation in the past is to monitor the frequency of the flashing from the consumer meter, which increases with rate of consumption, and this is not happening.
As I pondered this with my multimeter connected to the element terminals, I saw the voltage drop to zero for a second, and then return to 240. This repeats every 4-10seconds. I observed the same on the input side of the thermostat after I'd noticed this.
This is where I'm out of my depth. The circuit isn't tripping the RCD, so it seems unlikely the element has a short circuit. I can hear a faint click and see an LED illuminate on the SSR when the RPi sends 3.3v to the GPIO. I don't hear or see it opening/closing in line with these voltage drops, but haven't yet probed the voltage before and after as I don't have a neutral handy there, it just switches the positive of one of the three 240v phases in the house. I don't know if anything else is on the same phase, it is entirely possible that there is not.
Is it possible that there's some kind of failure mode of the element that could cause the conditions observed? The thermostat appears to be working, I feel like the SSR is doing what it always has - would appreciate any suggestions.
Cheers,
Alex
I wrote and fine-tuned some python code which establishes at midday each day how long it feels it should run the immersion heater based primarily upon the insolation of the NE PV array until that point, but also considering season, ambient temperature and forecast (these values are all scraped from the web rather than measured locally.
The way in which this controls the immersion heater is by way of an SSR, which remarkably (to me) was able to energise from just the 3.3v logic level signal from the RPi GPIO. It has worked well for ~8yrs, but yesterday we had cold water.
Testing the system from bottom to top, the RPi is up and responsive. It's giving up 3.3v on it's GPIO on demand, and this is readable at the SSR in the roof. Switching the GPIO in software gives rise to 240vac reaching the thermostat, and that in turn gives up 240vac to the element terminals when water temp is below the setting of the thermostat, typically about 60 celcius.
The thing is, the way in which I have established if the element is in operation in the past is to monitor the frequency of the flashing from the consumer meter, which increases with rate of consumption, and this is not happening.
As I pondered this with my multimeter connected to the element terminals, I saw the voltage drop to zero for a second, and then return to 240. This repeats every 4-10seconds. I observed the same on the input side of the thermostat after I'd noticed this.
This is where I'm out of my depth. The circuit isn't tripping the RCD, so it seems unlikely the element has a short circuit. I can hear a faint click and see an LED illuminate on the SSR when the RPi sends 3.3v to the GPIO. I don't hear or see it opening/closing in line with these voltage drops, but haven't yet probed the voltage before and after as I don't have a neutral handy there, it just switches the positive of one of the three 240v phases in the house. I don't know if anything else is on the same phase, it is entirely possible that there is not.
Is it possible that there's some kind of failure mode of the element that could cause the conditions observed? The thermostat appears to be working, I feel like the SSR is doing what it always has - would appreciate any suggestions.
Cheers,
Alex