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I am rebuilding my printer, a hold Prusa/Mendel that has been boxed for years. I have changed the board ( I am using a Rumba) and the drivers (I am using Pololu 8225) with heatsinks and 1/16 microsteps.

5 motors type 42BYGHW811, rated: 2,5 A, R 1,25 Ohm. I have set the stepper voltage at 0,8 V for XYE which gives a current of 0,64 A and they seems to work without problems.

To get the same current on Z, where I have 2 motors in parallel, I should set it at 0,4 V but the motors do not turn at such low voltage. They just make noise, no turn. I have M8 rods nicely lubricated on such axis and I can turn them easily by fingers. If I go up to 1 V the motors turns but then the driver gets very hot and I loose steps. May be I should play with the acceleration too?

I am not sure if the above settings are correct. Your hints from your actual settings and experiences will be appreciated.

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If the motors are in parallel, then setting it at 0.4V means each motor will only get a quarter of the current a single motor would get at 0.8V. If you set it to 0.8V each motor will get half. I think 0.8V (same as for the other motors) would be an appropriate setting. Stepper drivers are constant-current, not constant-voltage.

Are the steps/mm for your Z-axis correct? Perhaps it's just trying to move too quickly.

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  • $\begingroup$ Thank you Tom. Happens when you are focusing on a problem on your own that the big picture is invisible. The issue was in the acceleration, I reduced it from the default 3000 to 1000 and the same also for the feed rate from 5 to 3 and it is now working fine. The stepper voltage is at 0,8 as per the others. $\endgroup$ – FeliceM Oct 24 '16 at 6:48

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