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Why you should power off when unattended

Posted by frankvdh 
Why you should power off when unattended
December 19, 2020 04:06PM


This was the A4988 Z stepper driver on my laser cutter as I found it after cutting. My control board is, as recommended by the manufacturer, mounted vertically on the gantry, not covered at all. When I replaced this stepper driver, everything worked as usual, so no fuses were blown.

NB that the Z stepper is only used for focussing before cutting, not at all during the cutting operation. So I guess that this could happen any time the board is powered up.

Apologies for the blurry photos.
Re: Why you should power off when unattended
December 19, 2020 09:12PM
I think those modules are poorly engineered. They can't dissipate enough heat because of the small size of the circuit board. You can get better controllers that don't use modular motor drivers...


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Why you should power off when unattended
December 20, 2020 03:02AM
Yeah, but this failure wasn't due to poor heat dissipation. There had to be a pretty good short circuit to peel up a layer of the board. And, as I said, this was the Z stepper on a laser cutter, so not actually doing any work.
Re: Why you should power off when unattended
April 23, 2021 01:11AM
I'm pretty sure those kind of stepper drivers run at constant current regardless of whether the motor is moving or not. With newer Trinamic drivers, current can be controlled by software, and set to a lower value when holding still. I always stick heatsinks on my stepper drivers regardless. And a fan for the ones on my CNC, which are that old style, and running NEMA23 motors which they're not really designed for. They used to get pretty darn hot with heatsinks alone, but only slightly warm to the touch with the fan. I'm sure they would have died with no heatsink or fan smiling smiley
Re: Why you should power off when unattended
December 05, 2021 06:54AM
just clarifying what i see in the comments above.

the old drivers may run at a constant voltage that was just set too high.. current is controlled by the resistance change of the LC circuit (coil and driver capacitance) and as motor cycles faster its resistance rises, and its current is controlled by a higher voltage to maintain power as its resistance changes. what more than likely happed was voltage setting was not properly adjusted for the burnt part. i would guess it was over powered. these stepper drivers use more current when at idle. someone never set this to proper current level or used motors that were not in spec at static hold force.

trinamic drivers can be less noise because of the more natural sinusoidal wave and better auto current draw sensing of driver. the square wave output of a usual stepper driver is not ideal and excess energy in square wave causes resonance. if stepper driver was tuned and only ran at one frequency it would be quiet as well. but we need acceleration as nature does not allow instant stops and starts without a tremendous power and the motor runs at different speeds when two or three axis are in motion as the idea is a line in any direction with a constant speed.this is also why laser cutters are quieter than 3d printers. the axis is not under much load, and it is a single speed after brief acceleration because it produces lines usually in raster at 90deg angles only.

trinamic produces a more pure signal rather than a chopped digital pulse wave and allows programming optimal power or auto tuning optimal power at many different speeds

so the same burnt effect could be had on either device new or old. however the ability of trinamic driver to program in multiple voltages allows better current control.
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