From 004edb961316682cfdb57a7c6166eb06b0d3ca55 Mon Sep 17 00:00:00 2001
From: Nicholas Seckar <nseckar@gmail.com>
Date: Thu, 3 Oct 2019 14:59:03 -0700
Subject: [PATCH] fan: Add off_below option for fans (#1897)

Below off_below the fan will be turned off. When configured correctly this
can prevent stalling, which may lead to overheating and failed fans. To
simplify calibration and use of this setting, off_below is applied in the
input duty cycle domain, prior to any scaling due to e.g. max_power.

Signed-off-by: Nicholas Seckar <nseckar@gmail.com>
---
 config/example.cfg   | 13 +++++++++++++
 klippy/extras/fan.py |  4 ++++
 2 files changed, 17 insertions(+)

diff --git a/config/example.cfg b/config/example.cfg
index ed33b3d6..f0c6f2c9 100644
--- a/config/example.cfg
+++ b/config/example.cfg
@@ -259,6 +259,19 @@ pin: ar9
 #kick_start_time: 0.100
 #   Time (in seconds) to run the fan at full speed when first enabling
 #   it (helps get the fan spinning). The default is 0.100 seconds.
+#off_below: 0.0
+#   The minimum input speed which will power the fan (expressed as a
+#   value from 0.0 to 1.0). When a speed lower than off_below is
+#   requested the fan will instead be turned off. This setting may be
+#   used to prevent fan stalls and to ensure kick starts are
+#   effective. The default is 0.0.
+#
+#   This setting should be recalibrated whenever max_power is adjusted.
+#   To calibrate this setting, start with off_below set to 0.0 and the
+#   fan spinning. Gradually lower the fan speed to determine the lowest
+#   input speed which reliably drives the fan without stalls. Set
+#   off_below to the duty cycle corresponding to this value (for
+#   example, 12% -> 0.12) or slightly higher.
 
 # Micro-controller information.
 [mcu]
diff --git a/klippy/extras/fan.py b/klippy/extras/fan.py
index 5f72a780..f11a9e86 100644
--- a/klippy/extras/fan.py
+++ b/klippy/extras/fan.py
@@ -16,6 +16,8 @@ class PrinterFan:
         self.max_power = config.getfloat('max_power', 1., above=0., maxval=1.)
         self.kick_start_time = config.getfloat('kick_start_time', 0.1,
                                                minval=0.)
+        self.off_below = config.getfloat(
+            'off_below', default=0., minval=0., maxval=1.)
         ppins = printer.lookup_object('pins')
         self.mcu_fan = ppins.setup_pin('pwm', config.get('pin'))
         self.mcu_fan.setup_max_duration(0.)
@@ -29,6 +31,8 @@ class PrinterFan:
     def handle_request_restart(self, print_time):
         self.set_speed(print_time, 0.)
     def set_speed(self, print_time, value):
+        if value < self.off_below:
+            value = 0.
         value = max(0., min(self.max_power, value * self.max_power))
         if value == self.last_fan_value:
             return