Stepper Motors (Part 6)

Part 12, 3, 4, 5, 6, 7, 8, 9

This post is about an other driver module which is very popular in the world of robots and 3D printers. These modules features the DRV8825 Stepper Motor Controller integrated circuit made by Texas Instrument (Datasheet available from >here<). Although many clones exist, it looks like Pololu was at the origin of this module.

drv8825

The DRV8825 is a micro-stepping bipolar stepper motor driver which features adjustable current limiting, over-current and over-temperature protection, and six micro-step resolutions (down to 1/32-step). It operates from 8.2 V to 45 V and can deliver up to approximately 1.5 A per phase without a heat sink or forced air flow (rated for up to 2.2 A per coil with sufficient additional cooling). The driver has a pin-out and interface that are nearly identical to those of our A4988 stepper motor driver carriers, so it can be used as a higher-performance drop-in replacement.

drv8825_1

The VELLEMANN Vertex 3D printer (aka K8400) features 4 to 5 (2 extruder configuration) of these drivers. They proved to be very reliable in spite of poor power dissipation. The amazing thing about these drivers is that most suppliers suggest the use of an heat aluminum heat dissipator mounted on top of the plastic enclosure of the driver chip itself, although most of you know that plastic has poor thermal transmission properties. The striking thing about it all is that the designers of most DRV8825 driver modules managed to create a strong thermal bounding between the bottom of the DRV8825 chip (which by the way feature a conductive metal pad) and the opposite side of the PCB thanks to through hole thermal bridges.

drv8825_2

So that the heat dissipator should be installed beneath the module meaning restricted exposure to air flows…Strange. Some argued that installing the chip upside down would restrict access to the current limiting trim pot. Quite true. But how often did you need to adjust this pot really ?

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