DRV8825: DRV8825 Overcurrent Protection

Leor,

If the drive method (decay mode, speed, micro step setting) is similar on X, Y and Z. I would think the load on Z axis could be heavy than X and Y axis.

Let us make sure it is OCP protection, not over temperature protection first. "If this analog current limit persists for longer than the OCP time, all FETs in the H-bridge will be disabled and the nFAULT pin will be driven low. The device remains disabled until either nRESET pin is applied, or VM is removed and reapplied."

When the DRV8825 on Z OCP is triggered, do you have to remove input source or toggling nRESET pin?

After we confirm the OCP, is it possible to check the winding current on Z axis operation? I want to know the DC current too high or a current spike triggering the OCP. Also, what other settings affect the Z axis operation? (BTW, I don't find the decay mode setting from the protoneer CNC shield v2.58/v2.60 webpage. )

Hi Wang,

Protoneer Pi Hat: https://wiki.protoneer.co.nz/Raspberry_Pi_CNC

Re: “When the DRV8825 on Z OCP is triggered, do you have to remove input source or toggling nRESET pin?”

We have to unplug the power from the Pi, we do not have access to the nRESET pin. The Pi provides power for the arduino chip on the protoneer board.

Sorry, missed an important detail, motors are not all the same.

X and Y motors are: 25253-01 Stepper Motor - NEMA 17 from INVENTABLES

Z axis motor is: NMB-MAT PM49M-048-CDQ3 (RK2-2162 01) Picture attached. (from a Hewlett Packard printer)

We do not have a spec for Z motor, can’t find one, so we’ve been approximating till the motor runs smoothly.

• We tried changing the microstepping on the Z to different values: 1/16, ½ step and full step

• We tried playing with acceleration and speed settings in GRBL.

This hasn’t resolved the issue, and it’s hard to say if any of it made it better since it’s so random.

I’ll need to get some special equipment to check the winding current on the Z motor; it’s hard to measure since it comes in pulses. I’ll try and get back to you on this.

Current should be pretty consistent generally since we are not pushing the limits in our application.

I’ve read some posts on the decay helping people with similar issues, would you be able to explain what decay does in this application. If we pursue this path, how do we figure it out?

Leor,

It seems OCP issue instead of the thermal issue because you have to unplug the power from the Pi to reset the DRV8825.
Since you don't have the Z motor spec, I can swap the X motor or Y motor with Z motor to find it is motor issue or load issue.

Decay mode is related to the winding ripple current. Right now, we don't know the root cause yet. More info more helps. Would you measure the winding current on a scope? When the failure is happened, we can catch the winding current at that moment to further confirm the OCP issue. We may find some abnormal waveform before the failure is happened.