OK this is interesting, but also differs. If I have read correctly, you’re circulating the water in the system as a whole.

I’m also using a solar setup, but I’m using a serpentine coil running a separate coolant liquid. The coolant is used since winter goes from -10 to minimim -20 degrees celsius.

What are your coldest months like?

Hmm, the heater element being controller disregarding your will is a bit of a bummer.

Thanks for clarifying, so you are indeed circulating the water itself, it’s not a separate line used as a heater. In this case you really are at the mercy of either your pump, pipe length, ambient temperature, insulation and/or sun intensity.

Have you monitored the temperature at the panel on the roof itself? Also, what type of insulation are you running on those pipes?

Yeah, that seems like a good way to go. 65 degrees at ground level is what I’d also expect. My assumption up top would be close to 90/95 degrees. Driving the pump more often would be interesting.

Yeah, just gonna chime in here real quick.

I went down this road just as you. I found out that most MOTs are rather weak for 18650 nickel strips.

You need a transformer rated around 1500 watts. Most are 700-900 watts. I ended up wiring 2 transformers in parallel. Also, make sure to remove the transformer’s shunts. They are a form of current limiting and will impact your amps at the end.

Finally, make sure to carefully regulate your pressure with the copper tips. High pressure does indeed equal a weaker weld.

AC in general is also not the best for very short pulses of welds. I have found that 40-60ms work best for 0.2 with around 1000amps. Anything less didn’t weld tbh and the MOT couldn’t pull amps fast enough. I tried all sorts of windings and cable thicknesses. I finally chose 6AWG and I’m happy enough with 2 transformers.