03. Heating Control Options - larry-athey/rpi-smart-still GitHub Wiki

NOTE: The RPi Smart Still controller now fully supports the Boilermaker which can optionally offload all boiler temperature management to it. The progressive temperature feature of the Boilermaker is replaced by a more granular internal method. You choose a time spread factor in hours and your boiler target temperature will increment every 5 minutes (rather than every 15 minutes) to span the lower and upper boiler temperature limits defined in your programs.

One of the most common questions I get from home distillers is why I went with a stepper motor and SCR power controller instead of a PID temperature controller. The main reason is because I didn't want to shut out people who use propane fired boilers, so I went with a stepper motor controller which allows the system to work with a gas valve on a propane burner.

For SCR power controllers that use a potentiometer, a simple Nema 17 stepper motor with a coupler is all you need. In my case, I use an L&Z Technology LNZ-10000K SCR power controller mounted to a 3/4" slab of oak along with the stepper motor and a flexible coupler. It's a 10,000 watt controller and is way overkill for my Still Spirits boiler, but I'm sure that it will work with many other electric boilers out there, even if they run on 220 volts AC.

You will need to use a higher torque stepper motor for gas valves on propane powered boilers, such as steppers with a built-in planetary gear box. However, you should keep in mind that this system has no means for triggering an igniter on a propane burner. So, use the manual heat jump functions at the bottom of the Management menu to turn up the stepper motor to light the burner, then return it to zero (your idle burn position) and then start your run. In a gas fired boiler, the zero position doesn't shut off the gas completely, you should have an upstream valve for that.

For SCR power controllers with a potentiometer and propane powered boilers, you want to tell the smart still controller that you are using an analog heating controller, even if the SCR power controller has a built-in digital volt meter. This causes the smart still controller to always turn the heating down to zero and then dial up to the setting. Digital SCR power controllers use an encoder dial and every click will result in a precise change, analog controllers and gas valves are not accurate when randomly dialing in both directions.

In my stepper motor driver circuit and code, I do not use step smoothing (micro stepping) because I want precise steps and step smoothing reduces the torque. You may want to mount your stepper motor with rubber grommets on the screws if the noise bothers you. I'm not concerned with the noise, but I know some people who seem to think that all mechanical noise is a bad thing. I just figured that I would add this note and suggested remedy for those people who actually are bothered by the noise.

NOTE: When configuring the heating in the user interface, remember that a straight stepper motor with no planetary gear box has 200 steps per rotation. If you are using a 4:1 gear box, there are 800 steps per rotation. Also, there is no point in going with anything larger than a Nema 17. You don't need a high current and high torque motor to turn a potentiometer, and the DRV8825 stepper driver likely won't run anything larger.

Boilermaker Usage

The RPi Smart Still controller will work with the Boilermaker in all four of its built-in operating modes. If you enable Boilermaker support in the heating configuration, you will notice that the configuration page has a completely different set of options the next time you load the page.

Boilermaker IP Address - You need to tell the RPi Smart Still controller the IP address of your Boilermaker here.

Boiler Temperature Management - This drop-down list determines how the boiler temperature is managed.

  1. RPi Smart Still Controller means that the Boilermaker runs in Constant Power mode so it is basically running as a digital SCR controller.
  2. Boilermaker Temperature Cruise means that the Boilermaker uses its internal high thermal velocity temperature control which is best suited for reflux mode runs.
  3. Boilermaker Brewing/Fermentation means that the Boilermaker uses its internal PID temperature control with low thermal velocity and is best suited for pot still runs.
  4. Boilermaker Cruise Then Brew starts out in mode 2 and then switches to mode 3 after the target temperature has been reached, this provides fast preheating before beginning PID mode.

Startup Power (%) - This tells the boilermaker what power level to start at in its first two operating modes.

Fallback Power (%) - This tells the boilermaker what power level to fall back to after the target temperature has been reached in its first two operating modes.

Fixed Temperature - This determines if the Boilermaker will be running in a fixed or progressive temperature fashion in its last two operating modes. If set to Yes then the low value of the boiler temperature range in your program is the target temperature that the Boilermaker will use to maintain. If set to No then the Boilermaker will run in a progressive temperature fashion.

Time Spread (hours) - If the previous setting is set to No then this determines how many hours the progressive temperature will be spread over after the boiler is up to its minimum operating temperature. This spans the entire lower and upper temperature range of the current program and the temperature is incremented every 5 minutes.