08. Auxiliary Relays For Pumps - larry-athey/rpi-smart-still GitHub Wiki
A feature not documented in the original prototype system was added by GitHub user FireflySE when he designed the Raspberry Pi Hat printed circuit board. A new item in the user interface under the Management menu has been added for controlling the relays that he added to the design.
These relays are connected to GPIO pins 17 and 27 if you so choose to add them to your existing system that was not based on the Pi hat. The on/off states of these relays are maintained across system reboots. These relays also operate totally independent of the programs and can be turned on/off during an active distillation run.
If you are running your system on cooling water that is circulated by pumps, make absolutely sure that your pumps are running and pressurizing the water against your condenser and dephlegmator cooling valves when you run the calibration routine. Depending on the amount of pressure, this can cause resistance against the valves and have an effect on the timing calculation.
If you intend to use relays for switching high current AC loads, I strongly recommend using solid state relays as close to the load as possible. The relays on the Raspberry Pi Hat should only be used for low current DC loads, such as pumps like you see used in the Still Spirits water pressure regulator, or the trigger line of a solid state relay.
Keep in mind that the typical impeller driven pond pumps that you see distillers running in their chiller barrels generally don't provide enough pressure to push water through the ball valves if they're choked down to 30% or less. There is no balance between too much reflux where you have no output and running in straight pot still mode.
This is why the Dephleg Driver device was created. This replaces the dephleg cooling valve all together and uses a PWM driven 400ml/minute peristaltic pump to control the dephlegmator cooling water flow. This mounts in the same footprint as the ball valve in the controller case and the RPi hat can't tell the difference between the two.