DRV8825 Fast Decay Mod

I finally went ahead and did it. I forced my DRV8825 drivers into fast decay mode. I've been thinking of doing this for a while. I tried the whole freewheeling diode thing (made things worse).

After looking at many other mods and the Texas Instrument datasheet, this is what I came up with.

Bringing the DECAY pin (pin 19 on the IC) to logic high (5v) sets the driver in fast decay mode. Pin 18 (nFAULT) isn't used in this configuration. It is tied to the SLEEP pin via a resistor (1.5kohm I think). Under normal operation, the FAULT pin isn't held at 5V.

That being said, the M3 pin on the top is right next to the FAULT pin. The M3 pin is at 5v when in 1/32 stepping mode. I tied the M3 and FAULT pins together on the topside.

Ignore the brown/orange color - that is from the liquid flux I was using. I'm too lazy to clean it up with some denatured alcohol.

This puts 5v on the FAULT pin, which sends 5v to the nFAULT pin on the IC. I then tied pins 18 & 19 together on the IC.


Success. Drivers are in Fast decay mode. Definitely a different noise. More high pitched and annoying, even though it seems 'quieter' and the motors seem to run smoother. I have not had a chance to really put it through the paces to see how it affects print quality.

Edited 3 time(s). Last edit at 10/08/2016 09:09AM by MrBaz.

Does that also work with the "normal" version of the drv8825 drivers, where the chip is on top of the PCB? Where did you get yours from?

I ran my delta with modded drv's and they only got loud while steppers were standing, which is almost never on a delta.

Quote
o_lampe
Does that also work with the "normal" version of the drv8825 drivers, where the chip is on top of the PCB? Where did you get yours from?

I ran my delta with modded drv's and they only got loud while steppers were standing, which is almost never on a delta.

I believe mine are the m20b version. The m20a version had the chip on the top. As far as I know, this hack should work, but crack out the multimeter and make sure. I purchased these from reprapdiscount along with my RUMBA that I'm not so happy with.

While running, they are quieter from what I can discern. As you mention, when the motors are simply holding/stationary is when that noise can get to you.

Edited 1 time(s). Last edit at 10/09/2016 10:51PM by MrBaz.

These are the CoolDRV designed by Kliment, and sold by RepRapDiscount.

[github.com]

Cheers
ePoxi