DRV8825 Vref question

Hi!

I am having trouble with my 8825´s because I can´t get them to work properly with my stepper motors.
I have 5 clones and 1 original one with the Vref on the via. Before I checked the voltage, I found out that by trimming the motors,
there is only a very thin slice on the pot dial which makes my motor working instead of ticking loud.

So, I decided to use my multimeter and see whats going on.

First thing I noticed, is that the trim pot on the original pololu had a beginning and an end, which was 0V to 3,3V. I noticed some resistant force when I tried to move the pot beyond the max/min.
The clones´s pot could be tuned around over and over again, so I measured them and they also went from 3,3V to 0V and then for maybe 5° there was 2V and then again 3,3V and so on.
Ok, that was measuring the max and min voltages. I then put a nema 14 to the DRV8825 and trimmed it to the position where it did not tick loud, but actually moves
Result:

The Nemas only work between 0V and 0,28V Vref which is way to little to drive a printer. I can easily stall the motor by stopping it by hand.
Above, from 0,3V to 3,3V the motor just ticks.
This happens with all 5 clone DRV8825s and with my original.

With reference voltages above the 280mV the drivers don´t warm up or such, so heat can´t be the problem.

Why do all my drivers behave this way? with every tried Nema and on different boards..RAMPS and on MKS-Gen ??
I used the 1/32 setting all the time.

Please help :-)

Try turning the pots over their full range a few times with the power off. With luck this will improve the contact and give you a smooth adjustment from 0V to whatever the maximum is.

I much prefer to use controller electronics with software-adjustable stepper motor current. It makes things so much easier. Electronics novices should not be required to adjust pots while reading voltages on a meter.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

The pots seem to work for my understanding... they behave quite linear from 3,3V down to 0V.. then for some degrees 2V and then 3,3V again and so on.

You´re using Nema 14 steppers, I´d be curious to see a datasheet or any tech data of them...
-Olaf