Stepper Driver Thermal Testing

As mentioned in my previous post I am working on an improvement on the original Stepstick design. I arranged for a test to be carried out on the original Pololu (green, A4988), a Pololu "Black Edition" (A4988 on a 4 layer board), A4982 Stepstick (bought from eBay, assumed thin copper and 2 layer board), and the prototype of my new design, provisionally called the "Ice Blue Stepstick". Each one was subjected to the same current and stepped through the same sequence with thermal images to see how efficient they are at heat dissipation. The result: the new design is more than 10% better than the Pololu Black Edition!

The test results in full are below:

Comparison of Stepper Driver boards

Thermal imaging tests carried out for Think3DPrint3D.

Set up

Thermal testing of various different stepper driver “shields” carried out using a test sketch.

•       Sketch set to run 10,000 x 100us steps clockwise followed by 15,000 x 50us steps counterclockwise, with a 200ms delay between direction changes.

•       Drivers were set to 1/16th microstepping with the current limit set to 1.25A.

•       Drivers were run for 5 minutes and a thermal image of the driver shield was taken at the end of that time, while the motor was still running.

•       No additional heatsinking was added to the stepper driver ICs.

•       The motors were all the same model, unloaded, 4.4kg/cm NEMA 17 motors used on many 3d printers.

Drivers tested were as follows:

1.    Stepstick - A4982 - TSSOP IC - 2 Layer PCB - 1oz copper 

2.    Pololu 1182 - A4988 - QFN IC - 2 Layer PCB - 2oz copper

3.    Pololu 2128 - A4988 - QFN IC - 4 Layer PCB - 2oz copper

4.    T3P3 Ice Blue Stepstick - A4982 - TSSOP IC - 4 Layer PCB - 2oz copper

Results

1.     Stepstick - A4982 - Max temp = 133.8C, thermal shutdown was occurring during the test. 

2.     Pololu Green - A4988 - 2 Layer - Max temp = 110.6C

3.     Pololu Black - A4988 - 4 Layer - Max temp = 88.8C

4.     T3P3  Stepstick – A4982 – Max temp = 79.0C

Discussion

The old Stepstick tested as number 1 as almost certainly built using 1Oz rather than 2Oz copper and is dual layered rather than 4 layered hence the worst thermal performance. In addition the supplier has not published their design changes from the original Stepstick so it is hard to see how thermally efficient (or not!) that design is.

Pololu claim a 20% improvement in thermal efficiency between the 2oz 2 layer board (no. 2) and the 2oz 4 layer board (no. 3) for the A4988 which these test results support.

The "Ice-Blue" Stepstick which is similar to the A4988 4-layer Black Edition Pololu runs slightly cooler than the Pololu, probably due to the larger heat dissipation area of the A4982 TSSOP package.

The 1.25A test current is higher than that used for most RepRap type 3D printers and heatsinking & a cooling fan would be recommended to further reduce the temperatures, even for the Black Pololu/Ice Blue Stepstick.

Stepstick re-design

The Pololu stepper motor driver carrier and the open source Stepstick are pretty ubiquitous now as stepper driver daughter boards for a wide range of 3D Printer controllers. The Pololu driver has gone through a few iterations and the latest Allegro based version is the "Black Edition" which we have been supplying for some time now. It runs significantly cooler than the older version but is more expensive.

At the same time there have been a number of variations on the Stepstick theme but these have either had a bad reputation for poor quality assembly or have not had the designs published and so were not open source.

In the quest to continue to reduce prices while keeping high quality I decided to redesign the Stepstick to use an A4982 on a 4 Layer, 2Oz copper PCB (same as the Pololu Black Edition), aiming in the design to maximise heat dissipation. At the same time I have incorporated the design changes recommended by Nophead to fix low current microstepping issues and also increased the range of current supported by the Stepstick to the full 2A that can theoretically be supplied by the A4982 chip. Schematic is below:

I have had some prototypes made and initial testing is very promising: They run a mendel 90 fine with no heatsinks, where the original Pololus on that machine needed heatsinking.

There is further testing to do and I will post an update on that shortly.

Update:  Thermal test results are in! : Stepper Driver Thermal Testing. 

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