Thermal shutdown [tour 10]

Thermal shutdown and current trip

On some controllers a thermal sensor is fitted (or can be fitted as an option) to detect the MOSFET temperature and reduce the available current if the heatsink overheats.

At high current, there are several components which can get hot, such as the copper track, the relays, the high-current soldered joints and the main capacitor(s). The exact distribution of all this heating depends entirely on your application, the motor and your wiring so it is outside our control.

Clearly the thermal sensor can only measure the temperature at one place (normally the internal heatsink) so, if your application is causing bits other than the heatsink to get hot, the thermal sensor may not sense overheating and cause safe shutdown.

Clearly, if you mount the controller so that the heatsink is well cooled, then something other than the MOSFETs is going to get hottest first under severe overload. You should therefore contact 4QD for advice if you think overheating may be a problem in your application.

Sensors fitted operate typically at 95°C – so the units can get quite hot before the sensor operates.

Do not confuse thermal shutdown with the automatic temperature compensating ‘Current limit’.

Associated with thermal shutdown is heatsinking: covered on the next page.

In the DNO controllers, the thermal sensor is omitted. In these, if the current limit is hit the controller will trip off, after a delay period.

Already fitted to

  • Pro-150
  • 4QD series
  • Pro-120
  • VTX-75

Not available on

  • 2QD series
  • Porter

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