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DRV8825 Vref question

Posted by Yellobello 
DRV8825 Vref question
September 23, 2015 11:37AM
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 :-)
Re: DRV8825 Vref question
September 23, 2015 12:30PM
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.



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

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: DRV8825 Vref question
September 23, 2015 03:26PM
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.
Re: DRV8825 Vref question
October 01, 2015 04:34AM
You´re using Nema 14 steppers, I´d be curious to see a datasheet or any tech data of them...
-Olaf
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