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Tabs are source too, and stepper current.

A project log for Arcus-3D-P1 - Pick and Place for 3D printers

Open source, mostly 3D printable, lightweight pick and place head for a standard groove mount

daren-schwenkeDaren Schwenke 09/24/2018 at 21:101 Comment

I know this.  But I somehow managed to have two of my mosfet tabs touching and blew basically an entire day trying to figure out why my command to turn on one light always turned on both.  The tabs were touching, so the outputs were tied together.  Fixed, so I now have independent control over each light.

I also reprinted both light rings in just nylon.  It's stronger that way.

Lastly, something is going on with my stepper drivers.  They don't work above 1.2A reliably anymore.

I was losing steps while homing sometimes, so I went all the way down to 100mm/sec max velocity and 800mm/sec2 acceleration, and the problem persisted.  I replaced my bypass caps, which seemed to help as they were definately borderline... minimum value and running at 14v for a 16v rated cap.  Problem still happened, just a little less often.

Turned up the current, problem got worse.  Turned the current down from 1.6A to 1.2A and the problem went away.  Moves faster than at the higher current.

The drivers aren't hot.  The steppers are a little warm at 1.6A, but they are rated at 2A and never exceed 60C running at 1.6A, so that should be fine.  (they start to degrade at about 80C).

I checked the power rail for dips, and my ground rail for a good stable logic level.  All good.

I don't get it.  I'm running them at 1.2A for now.

Discussions

Teemo wrote 04/13/2019 at 06:45 point

Probably the supply voltage is too low for the steppers used. The current never reaches the set value, and then you lose microstepping. Motor coils resistance too high. Turning down the current is the right solution. You get what is possible from those motors at the selected supply voltage. I had the same problem with one of my motors.

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