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TMC2100 driving dual Z - thermal shutdown?

Posted by 3dflat 
TMC2100 driving dual Z - thermal shutdown?
December 27, 2017 12:36PM
I have a Tevo Tarantula-style printer with dual Z (two identical motors connected to a single TMC2100 in parallel) with MKS Gen 1.4 board.

With Vref set to 1.2V, making RMS 1.2V*0.7A/V = 0.84A, which does not seem excessive.

Symptom: about 20-30 minutes into the print, Z axis stops moving. It's pretty easy to rotate by hand, you can feel the steps, but not much resistance.

Hypothesis: thermal shutdown?

Head scratchers:
1. Cancel the print, then immediately go to Control and move Z axis, it moves as if nothing was happening!
2. I run X and Y closer to 1.4V, and their motors get to 45C with no ill effects. Z motors are barely 28C (but there are two in parallel, remember!)
3. Measuring temperature optically through the cooling fins reports ~27C on Z driver, 28-29C on X and Y. Does not look anywhere close to panic levels.

Any ideas?
Re: TMC2100 driving dual Z - thermal shutdown?
December 28, 2017 01:15AM
Two motors parallel might produce more noise (EMC-noise ) on the motor wires than the TMC2100 can take?
You can try to wire them in series or use a different driver like A4988.

But I'm just wild guessing....
Re: TMC2100 driving dual Z - thermal shutdown?
December 28, 2017 03:17PM
I almost convinced myself it was thermal. Vref was at 1.6V - over the "1.5 max / 1.3 max recommended", so I was running in the red zone. Backed to Vref=1.3V, works fine for now. The motors are dead cold, but there is almost no torque required to move that Z carriage anyway. I was not solving any real problem by increasing that Vref.
Re: TMC2100 driving dual Z - thermal shutdown?
December 29, 2017 12:53AM
Steppers will get hot, no matter if they stand still or move. Yours are cold, because they share the current by running them parallel.
Re: TMC2100 driving dual Z - thermal shutdown?
December 29, 2017 01:11AM
You haven't told us what Z motors you are using; but the types of motor typically used in 3D printers are better connected in series instead of in parallel, so that you can more easily drive them at a suitable current.


Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]

Large delta printer, and other 3D printer blog postings: [miscsolutions.wordpress.com]

Disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet [www.duet3d.com].
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