When I set up my OpensprinklerPi, I needed DC to operate the pump relay. I chose to make up my own full wave rectifier with a ripple filter to convert the AC from output 1 to DC to switch the pump relay. It works for a while but then fails after a while. I replace the triac and it runs for a while but eventually dies.
I could replace the triac with an NPN. But I’d rather keep my rectifier, since it is already built and housed in the box. Do you think it is spikes killing the triac or is it something else maybe. Should I bite the bullet and replace it with an NPN transistor, or should I try putting a snubber diode on Cannel 1
First, I need to understand where you placed the full-wave rectifier. I assume you added it between COM and say station 1? If would be best if you can provide a sketch. Note that you should not replace the half-wave recfitier (used for 24VAC to 5VDC conversion) on the OSPi with a full-wave rectifier — this is because the control mechanism of OSPi requires a half-wave rectifier, if you replace that with full-wave rectifier, it is not going to work.
Second, it’s possible to directly replace a triac with an NPN transistor. The triac’s G, MT1, MT2 pins are functionally equivalent to an NPN transistor’s B, E, C pins. If you intend to only replace 1 triac with transistor, you may consider making use of the built-in relay instead (the relay is rated 250VAC/3A, however, I recommend only using the relay for low voltages, such as below 40V, because the PCB traces and the enclosure are not rated 250VAC).
Lastly, a question: what type of pump relay do you have? A lot of sprinkler pump relays operate on 24VAC, so I am not sure how you can get them to work by converting 24VAC to DC.