Centroid Community CNC Support Forum

Marty...

Some like Chevys some like Ford's.

Agree completely. Around here it's:
"Friends don't let friends drive Fords" and "On a clear night you can hear the Chevys rust". Kind of like a Tastes Great vs. Less Filling argument and just as important!

Don't get me wrong, my latest ShopBot controller uses the G251X drive from Gecko as it (the controller) is designed for those old Oriental PK 296/299 motors with inductance going up into the 30's. They are old and were actually designed to use line voltage drives which put out rectified dc from 120vac drives (120 * sqrt 2 = 170vdc) which matches the high inductance (sqrt 30 = 5.47 * 32 = 175) of these motors by design. The only LeadShine drive that runs them well is the DM1182 with 120vac input. Gecko was smart enough to build drives that can accommodate this high inductance (specs say 1 to 50mh) on lower voltage DC and take advantage of the booming DIY CNC market in the early 2000's. Good for them, I love capitalism.

That said, based on other mfgr's specs and conversations with their product engineers, the "sqrt(Inductance) * 32" rule doesn't apply directly to their drives. And so far it has only applied to me as it relates to this new controller which will be built and supported by one of my sub builders:

viewtopic.php?f=62&t=6513

martyscncgarage wrote: ↑Tue Nov 30, 2021 10:19 am

Nigelo wrote: ↑Tue Nov 30, 2021 10:14 am Mike Richards has shown a formula above which is identical to Gecko Drive's own recommended equation 32 * SQRT (Inductance in Mh) = VMAX for calculating the safe max voltage for stepper motor operation. This is shown in Section 6 of their article https://www.geckodrive.com/support/step ... asics.html

I use this formula (as do many others) provided the result does not exceed 20 x stepper nominal voltage.

I answered the OP on the unofficial FB group based on his motor spec sheet that 60v is 25% below max 80.5v calculated on above formula based on inductance of 6.336 mh (i.e. 7.92mh less 20% variance for safety). Max 80.5v is marginally less than 20 x nominal voltage of 4.2v

Dr D may disagree and with no disrespect, I prefer to be guided by a reputable driver manufacturer whose guidance is used by so many without issue

hope this helps

And it is spot on.
The spec sheet says the inductance rating of your motors is 7.9. Square root of 7.9 is 2.81 * 32= 89VDC I would run them just under that voltage to have optimal speed and torque.

Provide the make and model of the stepper DRIVES along with the manual please....you probably have inexpensive stepper drives with no Current Reduction when the drive is idle (no step and direction commands being received)
Marty

Just a small point for clarification. The spec sheet does indeed show inductance of 7.9mh BUT with a variation of +/- 20%. Since we are calculating max voltage for safety, I therefore deducted 20% resulting in 6.336mh for the purpose of calculation

vw_chuck wrote: ↑Mon Nov 29, 2021 11:37 am Yea mine get hot just sitting. I run big ass Nema 23's. Touchable but still pretty warm.

I got a chuckle out of this comment. My metric frame 130 mm servo motors eat (big ass) NEMA 23's for breakfast.

ShawnM wrote: ↑Wed Dec 01, 2021 8:28 pm

vw_chuck wrote: ↑Mon Nov 29, 2021 11:37 am Yea mine get hot just sitting. I run big ass Nema 23's. Touchable but still pretty warm.

I got a chuckle out of this comment. My metric frame 130 mm servo motors eat (big ass) NEMA 23's for breakfast.

ikr. I am guilty of only having nema 34 servos on my mill, but anything with less than a 1in diameter shaft is small at my work. Especially once you start getting into rotary press converting. Everything is 4kw servo with a big gearbox, or larger. A 13in station Delta ModTech is about the smallest we go.

And for a chuckle, here is what happens when a 100:1 reduction nema 34 stalls. (thats only a 1/2in shaft, but still a bit of torque eh)

Yea that is funny as a Nema23 is tiny. I was referring to the length they are the long ass nema23's that use. Yea when mine stalls nothing happens. Just makes a thumping noise. I would rather them stall then break shit when I crash my machine.

@rk9268vc Nema34 with a 100:1 reduction is approximately equivalent to the 1960's Pontiac GTO engine. So yeah that can do some damage.