# Thermistor

A 100 kΩ NTC thermistor on the motor lets the driver stop before the motor overheats. It is optional, and off by
default; use it on any motor that runs near its rated current for long.

!!! warning "Without it, nothing protects the motor from overheating"
    The driver limits the current, not the temperature. A motor that runs continuously, holds a load for long, or
    is set up badly (a current limit above its rating, loops that oscillate, a wrong resistance or inductance) can
    overheat and burn its windings without any warning. With the thermistor fitted and enabled, the driver stops
    first. The starter kit includes one.

![The thermistor on its 2-pin connector.](https://docs.source-robotics.com/STEPFOC-docs/108/assets/STEPFOC_THERMISTOR-Photoroom.webp){ width="520" }

## Fitting it

A stepper is sealed: the windings cannot be reached. Place the thermistor on the motor housing, as close to the
windings as possible: either glued to the side of the housing, or in one of the four screw holes of the motor's
bottom with the screw removed, which puts it deep in the stack. Thermal cement holds it and conducts the heat.

<figure markdown="span">
  ![Thermal cement](https://docs.source-robotics.com/STEPFOC-docs/108/assets/Thermal_cement.webp){ width="220" }
  <figcaption>Thermal cement: it sets hard and conducts heat. Thermal paste stays soft and lets the bead move, ordinary glue insulates it. <a href="https://s.click.aliexpress.com/e/_c3dBOwTD" target="_blank" rel="noopener">Where to buy it</a>.</figcaption>
</figure>

The housing lags behind the windings by some seconds, and reads lower. Set the limit with that in mind: the
default of 75 °C at the housing corresponds to a hotter winding.

## Enabling it

```
#Term 1
#Tlim 75
#Save
```

`#Temp` then prints the temperature; with the thermistor disabled it prints `Temp Off`. Above the limit the driver
raises a temperature error and stops; it clears with `#Clear` once the motor has cooled.

Over CAN, Send_Respond_Temperature returns the temperature, and the temperature error is one of the bits of
Send_Respond_State_of_Errors.