Merge PR #2118

Marlin/Configuration_adv.h

 // before setting a PWM value. (Does not work with software PWM for fan on Sanguinololu)
 //#define FAN_KICKSTART_TIME 100
 
+// This defines the minimal speed for the main fan, run in PWM mode
+// to enable uncomment and set minimal PWM speed for reliable running (1-255)
+// if fan speed is [1 - (FAN_MIN_PWM-1)] it is set to FAN_MIN_PWM
+//#define FAN_MIN_PWM 50
+
 // @section extruder
 
 // Extruder cooling fans

Marlin/example_configurations/Felix/Configuration_adv.h

 // before setting a PWM value. (Does not work with software PWM for fan on Sanguinololu)
 //#define FAN_KICKSTART_TIME 100
 
+// This defines the minimal speed for the main fan, run in PWM mode
+// to enable uncomment and set minimal PWM speed for reliable running (1-255)
+// if fan speed is [1 - (FAN_MIN_PWM-1)] it is set to FAN_MIN_PWM
+//#define FAN_MIN_PWM 50
+
 // @section extruder
 
 // Extruder cooling fans

Marlin/example_configurations/Hephestos/Configuration_adv.h

 // before setting a PWM value. (Does not work with software PWM for fan on Sanguinololu)
 //#define FAN_KICKSTART_TIME 100
 
+// This defines the minimal speed for the main fan, run in PWM mode
+// to enable uncomment and set minimal PWM speed for reliable running (1-255)
+// if fan speed is [1 - (FAN_MIN_PWM-1)] it is set to FAN_MIN_PWM
+//#define FAN_MIN_PWM 50
+
 // @section extruder
 
 // Extruder cooling fans

Marlin/example_configurations/K8200/Configuration_adv.h

 // before setting a PWM value. (Does not work with software PWM for fan on Sanguinololu)
 //#define FAN_KICKSTART_TIME 100
 
+// This defines the minimal speed for the main fan, run in PWM mode
+// to enable uncomment and set minimal PWM speed for reliable running (1-255)
+// if fan speed is [1 - (FAN_MIN_PWM-1)] it is set to FAN_MIN_PWM
+#define FAN_MIN_PWM 50 // K8200: fan stops running at about 35 to 40 (of 255)
+
 // @section extruder
 
 // Extruder cooling fans

Marlin/example_configurations/SCARA/Configuration_adv.h

 // before setting a PWM value. (Does not work with software PWM for fan on Sanguinololu)
 //#define FAN_KICKSTART_TIME 100
 
+// This defines the minimal speed for the main fan, run in PWM mode
+// to enable uncomment and set minimal PWM speed for reliable running (1-255)
+// if fan speed is [1 - (FAN_MIN_PWM-1)] it is set to FAN_MIN_PWM
+//#define FAN_MIN_PWM 50
+
 // @section extruder
 
 // Extruder cooling fans

Marlin/example_configurations/WITBOX/Configuration_adv.h

 // before setting a PWM value. (Does not work with software PWM for fan on Sanguinololu)
 //#define FAN_KICKSTART_TIME 100
 
+// This defines the minimal speed for the main fan, run in PWM mode
+// to enable uncomment and set minimal PWM speed for reliable running (1-255)
+// if fan speed is [1 - (FAN_MIN_PWM-1)] it is set to FAN_MIN_PWM
+//#define FAN_MIN_PWM 50
+
 // @section extruder
 
 // Extruder cooling fans

Marlin/example_configurations/delta/biv2.5/Configuration_adv.h

 // before setting a PWM value. (Does not work with software PWM for fan on Sanguinololu)
 //#define FAN_KICKSTART_TIME 100
 
+// This defines the minimal speed for the main fan, run in PWM mode
+// to enable uncomment and set minimal PWM speed for reliable running (1-255)
+// if fan speed is [1 - (FAN_MIN_PWM-1)] it is set to FAN_MIN_PWM
+//#define FAN_MIN_PWM 50
+
 // @section extruder
 
 // Extruder cooling fans

Marlin/example_configurations/delta/generic/Configuration_adv.h

 // before setting a PWM value. (Does not work with software PWM for fan on Sanguinololu)
 //#define FAN_KICKSTART_TIME 100
 
+// This defines the minimal speed for the main fan, run in PWM mode
+// to enable uncomment and set minimal PWM speed for reliable running (1-255)
+// if fan speed is [1 - (FAN_MIN_PWM-1)] it is set to FAN_MIN_PWM
+//#define FAN_MIN_PWM 50
+
 // @section extruder
 
 // Extruder cooling fans

Marlin/example_configurations/delta/kossel_mini/Configuration_adv.h

 // before setting a PWM value. (Does not work with software PWM for fan on Sanguinololu)
 //#define FAN_KICKSTART_TIME 100
 
+// This defines the minimal speed for the main fan, run in PWM mode
+// to enable uncomment and set minimal PWM speed for reliable running (1-255)
+// if fan speed is [1 - (FAN_MIN_PWM-1)] it is set to FAN_MIN_PWM
+//#define FAN_MIN_PWM 50
+
 // @section extruder
 
 // Extruder cooling fans

Marlin/example_configurations/makibox/Configuration_adv.h

 // before setting a PWM value. (Does not work with software PWM for fan on Sanguinololu)
 //#define FAN_KICKSTART_TIME 100
 
+// This defines the minimal speed for the main fan, run in PWM mode
+// to enable uncomment and set minimal PWM speed for reliable running (1-255)
+// if fan speed is [1 - (FAN_MIN_PWM-1)] it is set to FAN_MIN_PWM
+//#define FAN_MIN_PWM 50
+
 // @section extruder
 
 // Extruder cooling fans

Marlin/example_configurations/tvrrug/Round2/Configuration_adv.h

 // before setting a PWM value. (Does not work with software PWM for fan on Sanguinololu)
 //#define FAN_KICKSTART_TIME 100
 
+// This defines the minimal speed for the main fan, run in PWM mode
+// to enable uncomment and set minimal PWM speed for reliable running (1-255)
+// if fan speed is [1 - (FAN_MIN_PWM-1)] it is set to FAN_MIN_PWM
+//#define FAN_MIN_PWM 50
+
 // @section extruder
 
 // Extruder cooling fans

Marlin/planner.cpp

         } else {
           fan_kick_end = 0;
         }
-    #endif//FAN_KICKSTART_TIME
+    #endif //FAN_KICKSTART_TIME
+    #ifdef FAN_MIN_PWM
+      #define CALC_FAN_SPEED (tail_fan_speed ? ( FAN_MIN_PWM + (tail_fan_speed * (255 - FAN_MIN_PWM)) / 255 ) : 0)
+    #else
+      #define CALC_FAN_SPEED tail_fan_speed
+    #endif // FAN_MIN_PWM
     #ifdef FAN_SOFT_PWM
-      fanSpeedSoftPwm = tail_fan_speed;
+      fanSpeedSoftPwm = CALC_FAN_SPEED;
     #else
-      analogWrite(FAN_PIN, tail_fan_speed);
-    #endif //!FAN_SOFT_PWM
+      analogWrite(FAN_PIN, CALC_FAN_SPEED);
+    #endif // FAN_SOFT_PWM
   #endif // HAS_FAN
 
   #ifdef AUTOTEMP