Yes the traces are pretty light for those kinds of currents, and I did have some concerns on the track spacing around the SCR and the screw terminals. The fatter tracks use a spacing for 240v that I looked up online.
Humidity here isn’t “tropical” as such, the board will probably get a coat of lacquer anyway.
The circulating pump is rated at 240v/20 watts (so not much current when it’s running steady state), and the SCR I’m using is good for a few amps of continuous current draw with a fairly high surge current. The SCR has minimal heatsinking so it will go first in extended high current situations, there’s going to be a panel mount fuse before all of this that I’ll probably set to 2 amps or so.
The zero-crossing SCR controller I’m using “should” prevent switching on the pump at the peaks of the mains cycle so max current should just be the initial stall current from the motor before it gets up to speed.
The pump is an induction motor so the only concern I’ve got is false triggering of the SCR and being unable to turn the pump off once triggered. I used an example snubber circuit from the data sheet of the zero crossing controller and of course they said “your milage may vary”.
At my latitude, never below 8 or 9 degrees C in winter. Maximum temperature is about 35 or 36 degrees C in summer.
Older systems here were simple thermosyphon designs on the roof with the holding tank closely coupled directly above the collectors and they were quite effective.
My system has a 330 litre mains pressure hot water tank, with the usual cold and hot fittings bottom and top. There is a third inlet about 1/3rd of the way up the tank, and a little bit above that is a heater element and a controlling thermostat. The lower third of the tank is circulated out via the cold inlet and up through the collector by the pump, which can do about 300 litres an hour. Hot water returns from the collector at the 1/3rd location, and rises to the top of the tank via stratification. The copper pipes to and from the collectors are 1/2" and are insulated, but their surface area to volume ratio is quite large and heat is easily lost over the 15 or so metres of pipework.
On sunny days I can see the inlet temperature at the bottom of the tank slowly rise from approx 20-25 degrees C to 30-35 degrees C as the bottom third circulates, the hotter water rises to the top to give the small temperature rise I can see at the top of the tank and the warm water layer slowly lowers towards the bottom of the tank.
Essentially I want a higher temperature returned to the tank, which I suspect can rather paradoxically be done by increasing the circulation rate when running the pump, peaking the collector temperature higher with the pump off then dumping that back to the tank rapidly, rather than the current controllers method of pulsing the pump and slowly circulating it to maintain a moderate collector temperature and losing the heat in the lines.
I have the service manual for the controller and it mentions frost protection, where it will circulate warmer water back to the collectors in low temperatures, but this would be insufficient for your colder climate.
At some stage I would also like to control the heater element, it runs on an off peak circuit which is switched by the electricity company when it suits them, so it is cheaper to run. It also means that it regularly “tops up” the top 2/3rds of the tank temperature, which negates the solar contribution a fair bit. I would like to be able to disable that top up if the system can sense adequate heating from the collectors, but that requires switching control to a 3kW element, and something I will leave alone for now.
The brain is a lazy thing. It falls into patterns easily, it takes mental shortcuts whereever it can. All that comes from our evolutionary history, where energy (literal energy for thinking) was limited.
Your subconscious mind handles all the everyday trivia to maintain your existence in a low energy way, and your mind is very quick to shunt things down that low energy path. That path is all our “instincts” (fight or flight, nurturing instincts, forming into groups etc etc ) and is based upon nomadic living in the savannah plains of Africa three million years ago.
If someone presents something in a way that can easily fall into one of our evolutionary shortcuts then your subconscious will run with it without you even realising.
Hmm I’m not sure of the pin drive currents on the Pico, but can you power the sensors off a pin? At least then you can programmatically power cycle them if you need to.
The Pico also has a watchdog, you could set it up to give it a reboot if things don’t respond in time. It doesn’t solve the issues of course but at least it gets it back to a workable state. And if the watchdog fails, or it works but there’s still no USB serial, then that would point towards power instabilities or somesuch.