Hi all,
Just did a brew with the boil kettle on a PID. The boil intensity varied a lot during the boil - from close to boil over to near nothing happening.
Is it possible to simply set the % time on of the element? If i could just dial it up to the optimal for my system it would be a lot easier than fiddling with the PID. Is this possible with the current software?
You can indeed use a PWM without a PID to control a boil, but we also have support for this in the PID itself.
If you open the PID settings, you can set the minimum boil output. Now when boiling (setpoint >= 100°C), output will always be at least that.
When you stop boiling (lower the setpoint), the setting is inactive.
This way you can both quickly reach boil temp, and maintain the boil with just enough power.
Does this work reliably?
The ‘Brew Boss’ systems has an algorithm for detecting boil (as the boil temperature can vary based on various conditions). Here’s an extract from the manual:
Boil Flag - This parameter tells the controller that we are trying to boil the contents of the kettle
and is only used for step types 3 and 4. As the temperature that a wort will boil is dependent on
the specific gravity of the wort and the barometric pressure, the temperature that the wort will
boil is unknown. Please note that water does not boil at 212F (100C) everywhere! It only
boils at 212F (100C) at seal level on a standard pressure (29.92 in Hg) day! If you are at a
higher altitude or barometric pressure is low, your wort may boil at as low as 205F. It is
important that the controller knows the boil temperature to maintain, otherwise it would stay at
full power through the entire process and would not know when boiling commenced. This flag
set to 1 tells the controller that it should detect boiling, once detected, store the temperature
value where the wort boiled for the following steps and then proceed to the next step. It is best
to set the setpoint for any step where you set the Boil Flag to 1 to a value of 220F or 105C,
guaranteeing it reaches boil. Set this value to 0 when setpoints for mashing, etc. are set. This
flag tells the application that we are not trying to reach a specific setpoint, instead, we want it to
determine automatically what the boiling temperature is for the current conditions. The
application looks at the slope of the temperature rise curve and determines when that slope
levels off, which is the point where the temperature ceases to rise. That indicates that the kettle
is boiling. At that time, the boil temperature is recorded, and the power is reduced to PwrB.
Make certain to set the Boil Flag for any step that involves boiling so that the program knows to
use the PwrB value.
The flag described here is set in the automation file used for setting up the brew steps.
Is there any plan to look into doing something similar?
The PID has a boil mode. It has a different combination of manual settings and automatic detection, but the idea (and result) is about the same.
More info at: https://brewblox.netlify.app/user/all_blocks.html#pid
I don’t think the detection is required, we chose a simpler approach.
If your setting is equal to or above 100C (configurable), we assume your goal is boiling and boil mode is enabled.
When boil mode is enabled, the PID output is clipped to a minimum so it keeps the boil going instead of going to zero when the temperature has been reached.
By going from the setting, we don’t need to know the exact actual boil temp.