Wednesday 5 April 2017

DuetWifi - Updated Thermal Testing

During the prototype development of the DuetWifi we carried out extensive thermal testing to validate the thermal characteristics of the PCB design. The two areas we looked at in detail were the TMC2660 stepper drivers and the high current heated bed MOSFET and associated traces and connectors. The results of this thermal testing allowed us to confidently set the stepper driver current to 2.0A in firmware and recommend a maximum heated bed current of 15A.

Now the DuetWifi has been in production for over 7 months, we have much more information about the performance of the board in the real world. This combined with updated the thermal testing (thanks again to Andy Hingston) has allowed us to make the following changes:

  • increased the recommended maximum heated bed current to 18A 
  • increased the stepper driver current limit will shortly be raised in firmware to 2.4A.

  • this is for production (blue) DuetWifi and upcoming DuetEthernet boards, not for the prototype (white) DuetWifis.
  • If setting stepper driver current higher than 2A ensure there is a fan blowing across the back of the Duet or Duex board.
  • When first using stepper driver currents higher than 2A use M122 to check for over temperature warnings. Future versions of the firmware will have additional functionality to reduce stepper drivers power intelligently if an over temperature warning occurs.

We also took the opportunity to test the Duex5 stepper drivers, these perform better than those on the DuetWifi as they have even more on-board heat sinking. There is more details on the testing results, and caveats, below.

DuetWifi Stepper Testing : 2.5A Half Step Hold*

DuetWifi Thermal Test 2.5A Half Step Hold - 123.3C - Front View
*See the previous thermal testing blog post for an explanation.

Duex5 Stepper Testing : 2.5A Half Step Hold

Duex5 Thermal Test 2.5A Half Step Hold - 102.3C - Front View

DuetWifi Heated Bed MOSFET Testing : 20A soak test

DuetWifi Thermal Test Heated Bed 20A 86.7C - Front View

DuetWifi Thermal Test Heated Bed 20A 77.1C - Front View
The tests were completed under the following conditions:
  • Board under test: DuetWifi v1.01, Duex5 V0.7
  • Ambient Temperature: 25-27C
  • Soak Time: 20 minutes