PID Controller turns off Output Lower (0%) despite "Always Min: True" when temperature is below Setpoint

[olegsolo73]

I am setting up a PID controller to manage the climate in a growbox by controlling an exhaust fan via PWM (MQTT Output). The fan is assigned to the Output Lower channel (Cooling).

Because plants require constant fresh air exchange (CO2) and negative pressure for odor control, the exhaust fan must never turn off completely. To achieve this, I set Output Lower Min On to 10.0% and enabled the Output Lower Always Min: True checkbox, which was introduced to solve exactly this in Issue #757.

However, the Always Min setting is completely ignored when the actual temperature drops below the Setpoint.

Here is the log showing the exact PID Configuration, confirming Always Min: True on the Output Lower channel
2026-03-04 00:43:51 - INFO - mycodo.controllers.controller_pid_d475b099 -
PID Settings: Direction: lower, Period: 30.0, Setpoint: 30.0, Kp: 1.0,
Output Lower Type: pwm, Output Lower Min On: 2.0, Output Lower Always Min: True

2026-03-04 00:26:14 - DEBUG - mycodo.controllers.controller_pid_f72cd48b -
Latest (CH0, Unit: C): 23.1 @ ...
2026-03-04 00:26:14 - DEBUG - mycodo.controllers.controller_pid_f72cd48b -
PID: Input: 23.1, Output: P: 1.89, I: 0.0, D: 0.0, Out: 1.89

[kizniche]

I found an issue with the use of incorrect variables for the PWM section of the PID controller. I pushed a potential fix 0a925d3. If you would like to upgrade to master to test the fix, let me know if ti solves the issue.

[olegsolo73]

Hey @kizniche,

I updated to the master branch to test your fix from commit 0a925d3, but it looks like the issue is still there.

The patch is installed, but the PWM values from the UI are not reaching the new variables in the code.

When I set "Min Duty Cycle (Lower)" to 15.0 in the UI, the log shows it's being saved to Output Lower Min On Duration, while the new Output Lower Min PWM variable stays as None.

Because Min PWM is None, the Always Min: True setting is still being ignored when the temperature drops below the setpoint, and the fan turns off completely.

Here is the log showing what the PID controller receives:

2026-03-04 09:18:01,000 - INFO - mycodo.controllers.controller_pid_2df695a9 - PID Settings: Device ID: 9f86017a-1738-4f58-b409-91a9e39a46ba, Measurement ID: 62361970-7b3e-45f5-820d-740765d1f184, Direction: lower, Period: 30.0, Setpoint: 30.0, Band: 0.0, Kp: 1.0, Ki: 0.0, Kd: 0.0, Integrator Min: -100.0, Integrator Max 100.0, Output Raise: None, Output Raise Channel: None, Output Raise Type: None, Output Raise Min On Duration: 0.0, Output Raise Max On Duration: 0.0, Output Raise Min Off Duration: 0.0, Output Raise Min PWM: None, Output Raise Max PWM: None, Output Raise Always Min PWM: False, Output Lower: 7a46425f-ca37-45b2-9f52-499e2b432617, Output Lower Channel: 0, Output Lower Type: pwm, Output Lower Min On Duration: 15.0, Output Lower Max On Duration: 80.0, Output Lower Min Off Duration: 0.0, Output Lower Min PWM: None, Output Lower Max PWM: None, Output Lower Always Min PWM: True, Setpoint Tracking Type: , Setpoint Tracking ID: 
2026-03-04 09:18:01,001 - INFO - mycodo.controllers.controller_pid_2df695a9 - Activated in 62.7 ms

[kizniche]

Okay, I didn't review the code enough. I reverted my last commit. You'll need to update to master to get that change. Can you provide a screenshot of your PID settings and a log of the PID operating with the PID setting "Log Level: Debug" enabled?

[olegsolo73]

hello!!! I've updated and here are my logs and a screening of the pid controller settings [image: image.png] 2026-03-05 06:58:30,313 - INFO - mycodo - All activated Trigger controllers started 2026-03-05 06:58:30,403 - INFO - mycodo - All activated Input controllers started 2026-03-05 06:58:30,404 - INFO - mycodo.controllers.controller_input_d03ef39b - Activated in 63.7 ms 2026-03-05 06:58:30,404 - INFO - mycodo - All activated PID controllers started 2026-03-05 06:58:30,404 - INFO - mycodo - All activated Function controllers started 2026-03-05 06:58:30,405 - INFO - mycodo.inputs.mqtt_paho_json_d03ef39b - Connected to localhost as client_r3nW6NXB 2026-03-05 06:58:30,464 - INFO - mycodo.controllers.controller_widget - Activated in 59.9 ms 2026-03-05 06:58:31,464 - INFO - mycodo - Mycodo daemon started in 1.862 seconds 2026-03-05 07:00:40,009 - INFO - mycodo.controllers.controller_pid_f72fe7fe - PID Settings: Device ID: d03ef39b-f020-4c86-9114-dd2ba1cfc48e, Measurement ID: e32a5ab6-43c1-4135-9974-a27bd49be21b, Direction: lower, Period: 30.0, Setpoint: 30.0, Band: 0.0, Kp: 1.0, Ki: 0.0, Kd: 0.0, Integrator Min: -100.0, Integrator Max 100.0, Output Raise: None, Output Raise Channel: None, Output Raise Type: None, Output Raise Min Amount: 0.0, Output Raise Max Amount: 0.0, Output Raise Min Off Duration: 0.0, Output Raise Always Min PWM: False, Output Lower: 7a46425f-ca37-45b2-9f52-499e2b432617, Output Lower Channel: 0, Output Lower Type: pwm, Output Lower Min Amount: 15.0, Output Lower Max Amount: 98.0, Output Lower Min Off Duration: 0.0, Output Lower Always Min PWM: True, Setpoint Tracking Type: , Setpoint Tracking ID: 2026-03-05 07:00:40,009 - INFO - mycodo.controllers.controller_pid_f72fe7fe - Activated in 135.6 ms 2026-03-05 07:01:10,153 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 20.69 @ 1970-01-21 15:24:43.265541 2026-03-05 07:01:10,154 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 20.69, Output: P: 9.309999999999999, I: 0.0, D: 0.0, Out: 9.309999999999999 2026-03-05 07:01:40,132 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 20.7 @ 1970-01-21 15:24:43.295542 2026-03-05 07:01:40,132 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 20.7, Output: P: 9.3, I: 0.0, D: -0.0, Out: 9.3 2026-03-05 07:02:10,206 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 20.71 @ 1970-01-21 15:24:43.325544 2026-03-05 07:02:10,207 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 20.71, Output: P: 9.29, I: 0.0, D: -0.0, Out: 9.29 2026-03-05 07:02:40,256 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 20.72 @ 1970-01-21 15:24:43.355549 2026-03-05 07:02:40,256 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 20.72, Output: P: 9.280000000000001, I: 0.0, D: -0.0, Out: 9.280000000000001 2026-03-05 07:03:10,124 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 20.73 @ 1970-01-21 15:24:43.385761 2026-03-05 07:03:10,124 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 20.73, Output: P: 9.27, I: 0.0, D: -0.0, Out: 9.27 2026-03-05 07:03:40,194 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 20.74 @ 1970-01-21 15:24:43.415579 2026-03-05 07:03:40,194 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 20.74, Output: P: 9.260000000000002, I: 0.0, D: -0.0, Out: 9.260000000000002 2026-03-05 07:04:10,173 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 20.75 @ 1970-01-21 15:24:43.445586 2026-03-05 07:04:10,174 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 20.75, Output: P: 9.25, I: 0.0, D: -0.0, Out: 9.25 2026-03-05 07:04:40,206 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 20.76 @ 1970-01-21 15:24:43.475610 2026-03-05 07:04:40,206 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 20.76, Output: P: -5.760000000000002, I: 0.0, D: -0.0, Out: -5.760000000000002 2026-03-05 07:04:40,236 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Setpoint: 15.0, Control Variable: -5.760000000000002, Output: PWM output 7a46425f-ca37-45b2-9f52-499e2b432617 CH0 to 19.2% 2026-03-05 07:05:10,211 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 20.77 @ 1970-01-21 15:24:43.505788 2026-03-05 07:05:10,212 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 20.77, Output: P: -5.77, I: 0.0, D: -0.0, Out: -5.77 2026-03-05 07:05:10,242 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Setpoint: 15.0, Control Variable: -5.77, Output: PWM output 7a46425f-ca37-45b2-9f52-499e2b432617 CH0 to 19.2% чт, 5 мар. 2026 г. в 01:18, Kyle Gabriel ***@***.***>:

…

Okay, I didn't review the code enough. I reverted my last commit. You'll need to update to master to get that change. Can you provide a screenshot of your PID settings and a log of the PID operating with the PID setting "Log Level: Debug" enabled? — Reply to this email directly, view it on GitHub <#1514 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/BGSRQTHRN6DCCZ3MFIYQ3634PCTSRAVCNFSM6AAAAACWF7AWS2VHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTMMBQGI4DIMI> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[kizniche]

Attachments need to be made through the website, attaching to an email reply will not work.

[kizniche]

I don't see in your log it setting the Output duty cycle below the 15 minimum you set. Can you show log lines where you see an issue?

[olegsolo73]

2026-03-05 07:24:40,159 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 21.11 @ 1970-01-21 15:24:44.676321 2026-03-05 07:24:40,159 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 21.11, Output: P: 8.89, I: 0.0, D: -0.0, Out: 8.89 чт, 5 мар. 2026 г. в 07:22, Kyle Gabriel ***@***.***>:

…

Also set log level debug for the Output and recapture some more log lines, please. — Reply to this email directly, view it on GitHub <#1514 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/BGSRQTA56SO6KV35VMLYDQL4PD6JRAVCNFSM6AAAAACWF7AWS2VHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTMMBQGUYDQNI> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[kizniche]

That's the control varible (8.89), that's not the output duty cycle. The line you would be looking for when the PID sets the duty cycle is as follows, for example:

2026-03-05 07:05:10,212 - DEBUG -
mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 20.77,
Output: P: -5.77, I: 0.0, D: -0.0, Out: -5.77
mycodo.controllers.controller_pid_f72fe7fe - Setpoint: 15.0, Control
Variable: -5.77, Output: PWM output
7a46425f-ca37-45b2-9f52-499e2b432617 CH0 to 19.2%

[olegsolo73]

[image: image.png] 2026-03-05 07:47:40,205 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 21.69 @ 1970-01-21 15:24:46.056926 2026-03-05 07:47:40,205 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 21.69, Output: P: 8.309999999999999, I: 0.0, D: -0.0, Out: 8.309999999999999 2026-03-05 07:48:10,179 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 21.7 @ 1970-01-21 15:24:46.086928 2026-03-05 07:48:10,179 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 21.7, Output: P: 8.3, I: 0.0, D: -0.0, Out: 8.3 2026-03-05 07:48:40,159 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 21.71 @ 1970-01-21 15:24:46.116932 2026-03-05 07:48:40,159 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 21.71, Output: P: 8.29, I: 0.0, D: -0.0, Out: 8.29 2026-03-05 07:49:10,231 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 21.72 @ 1970-01-21 15:24:46.146937 2026-03-05 07:49:10,232 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 21.72, Output: P: 8.280000000000001, I: 0.0, D: -0.0, Out: 8.280000000000001 2026-03-05 07:49:40,198 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 21.74 @ 1970-01-21 15:24:46.176941 2026-03-05 07:49:40,198 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 21.74, Output: P: 8.260000000000002, I: 0.0, D: -0.0, Out: 8.260000000000002 2026-03-05 07:50:10,182 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 21.75 @ 1970-01-21 15:24:46.206947 2026-03-05 07:50:10,182 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 21.75, Output: P: 8.25, I: 0.0, D: -0.0, Out: 8.25 2026-03-05 07:50:40,158 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 21.77 @ 1970-01-21 15:24:46.236844 2026-03-05 07:50:40,159 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 21.77, Output: P: 8.23, I: 0.0, D: -0.0, Out: 8.23 2026-03-05 07:51:10,139 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 21.78 @ 1970-01-21 15:24:46.266851 2026-03-05 07:51:10,139 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 21.78, Output: P: 8.219999999999999, I: 0.0, D: -0.0, Out: 8.219999999999999 2026-03-05 07:51:40,202 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 21.8 @ 1970-01-21 15:24:46.296855 2026-03-05 07:51:40,203 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 21.8, Output: P: 8.2, I: 0.0, D: -0.0, Out: 8.2 2026-03-05 07:52:10,179 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 21.81 @ 1970-01-21 15:24:46.326860 2026-03-05 07:52:10,179 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 21.81, Output: P: 8.190000000000001, I: 0.0, D: -0.0, Out: 8.190000000000001 2026-03-05 07:52:40,158 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 21.83 @ 1970-01-21 15:24:46.356863 2026-03-05 07:52:40,158 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 21.83, Output: P: 8.170000000000002, I: 0.0, D: -0.0, Out: 8.170000000000002 2026-03-05 07:53:10,141 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 21.84 @ 1970-01-21 15:24:46.386873 2026-03-05 07:53:10,141 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 21.84, Output: P: 8.16, I: 0.0, D: -0.0, Out: 8.16 2026-03-05 07:53:40,164 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 21.85 @ 1970-01-21 15:24:46.416881 2026-03-05 07:53:40,165 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 21.85, Output: P: 8.149999999999999, I: 0.0, D: -0.0, Out: 8.149999999999999 2026-03-05 07:54:10,144 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 21.86 @ 1970-01-21 15:24:46.447097 2026-03-05 07:54:10,144 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 21.86, Output: P: 8.14, I: 0.0, D: -0.0, Out: 8.14 2026-03-05 07:54:40,218 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - Latest (CH0, Unit: C): 21.87 @ 1970-01-21 15:24:46.477087 2026-03-05 07:54:40,218 - DEBUG - mycodo.controllers.controller_pid_f72fe7fe - PID: Input: 21.87, Output: P: 8.129999999999999, I: 0.0, D: -0.0, Out: 8.129999999999999 чт, 5 мар. 2026 г. в 07:28, Kyle Gabriel ***@***.***>:

…

That's the control varible (8.89), that's not the output duty cycle. The line you would be looking for when the PID sets the duty cycle is as follows, for example: mycodo.controllers.controller_pid_f72fe7fe - Setpoint: 15.0, Control Variable: -5.77, Output: PWM output 7a46425f-ca37-45b2-9f52-499e2b432617 CH0 to 19.2% — Reply to this email directly, view it on GitHub <#1514 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/BGSRQTFM5CDLMFELT57P3Q34PD7ANAVCNFSM6AAAAACWF7AWS2VHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTMMBQGUYTCMI> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[kizniche]

Also again, any image attacents you add to an email reply are discarded. You need to post attachments at github.com.
The duty cycle of the output is not changed in the log you just posted. Again, the log line that shows the output duty cycle being changed looks like the following:
mycodo.controllers.controller_pid_f72fe7fe - Setpoint: 15.0, Control Variable: -5.77, Output: PWM output
7a46425f-ca37-45b2-9f52-499e2b432617 CH0 to 19.2%

The duty cycle was changed to 19.2%. None of your logs have shown the duty cycle being set lower than the minimum 15% you have set.